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Stalagmite Evidence from Belize Indicating Significant Droughts at the Time of Preclassic Abandonment, the Maya Hiatus, and the Classic Maya Collapse
Abstract
Paleoenvironmental data from a stalagmite from western Belize provide a 3300-year record of droughts that impacted the Maya civilization at least four times across a span of 1500 years, and the most sustained period of drought coincided with the collapse of Classic Maya civilization. The stalagmite, which comes from Macal Chasm in the Vaca Plateau, provides reliably dated reflectance, color, luminescence, and C and O stable isotope records for the period from 1225 B.C. to the present. The record thus encompasses the Maya Preclassic, Classic, and Postclassic periods. The Maya civilization peaked in population density and socioeconomic complexity during the Classic period extending from A.D. 25 to 900, but it declined abruptly over the years from A.D. 750 and 900. The stalagmite record indicates that a series of droughts, which collectively form the most prolonged dry interval in the 3300-year record, lasted from A.D. 700 to 1135 and thus coincided with the collapse of the Maya civilization. In addition, two earlier droughts evident in the stalagmite record coincided with the Preclassic Abandonment and the Maya Hiatus, two earlier declines in Maya civilization. A drought in the mid-1400s recorded in post-Classic documents is also evident in the stalagmite record. Collectively, these findings illustrate the dependence of Mayan civilization on water supplies and the impact of declining water resources on a vibrant civilization.
... In this paper, the time frames for the Maya Abandonment and the Maya Hiatus proposed by Gill (2000) are used, whilst the period established for the Maya Collapse is based on Grube et al., (2012) and Douglas et al., (2016b), who argued that the collapse started 50 years before the first massive drought at 1140 BP inferred by Gill (2000). It has to be highlighted that the first drought during the collapse has been observed around 740 BP in some palaeorecords (Evans et al., 2018;Webster et al., 2007). Gill (2000) based his hypothesis mainly on the findings of the sediments of Lake Chichancanab where layers of gypsum were indicative of strong droughts during the time of the collapse (Hodell et al., 1995(Hodell et al., , 2005a. ...
... Fourteen records were developed using speleothems (Akers et al., 2016(Akers et al., , 2019Kennett et al., 2012;Frappier et al., 2002Frappier et al., , 2007Frappier et al., , 2014Medina-Elizalde and Rohling 2012;Medina-Elizalde et al., 2016a,b;Pollock et al., 2016;Ridley 2014;Ridley et al., 2015;Serrato Marks et al., 2021;Smyth et al., 2011Smyth et al., , 2017Warken et al., 2021;Webster et al., 2007;Wiseman 1985), in two occasions, two speleothems come from the same site, e.g. Río Secreto (Medina-Elizalde et al., 2016b;Serrato Marks et al., 2021) and Yok Balum, Lechleitner et al., 2015) but covering different periods. ...
... Some speleothems have a chronology established with numerous dated points, which possess relatively minimal uncertainties, e.g. the speleothems at Macal Chasm (Akers et al., 2016;Webster et al., 2007) and Rey Marcos (Winter et al., 2020), although correction for the presence of detrital material is typically applied (Bernal et al., 2006(Bernal et al., , 2010. Speleothems can also potentially be annually layered, allowing high-resolution chronologies to be established, similar to those using varves in lakes. ...
Palaeoclimatic research has been performed in the Maya Area (MA), using mainly lake sediment cores and speleothems. Most of the studies have been performed in the lowlands, leaving the highlands unexplored. Lake sediments records contain a diversity of proxies (e.g. Mineralogy, isotopes, pollen, charcoal, diatoms, chemicals, magnetic susceptibility, among others) and temporal resolution, making them frequently not easy to compare and leaving numerous gaps of information. Practically all stalagmites are focused on using δ18O as a proxy of effective rainfall during the Maya periods, having only some explored the role of palaeostorms and hurricanes as well as the paleoclimatology of the pre-Maya and modern periods. In this review paper, the location and temporal frame of palaeoenvironmental records of the MA and their proxies are presented, showing the zones and periods that possess environmental information and assessing their resolution. The comparison shows that more high-resolution records with a multi-proxy approach covering most of the Holocene are needed to understand the climate change in different zones of the MA. Finally, the geographic distribution of the diverse recorded hydroclimate responses based on the records is presented for three critical moments in the Maya History that have been associated with dry periods in the Great Maya Droughts hypothesis. This geographic perspective shows that dry events were not presented in all the MA during these moments although they were vastly recorded in both high- and lowlands. The geographic perspective also shows a negligible drought effect in the central lowlands for the Maya Hiatus period, where this cultural phenomenon was identified first. But signals of droughts are presented in other zones of the MA for this period. The distribution of the drought signal also shows that sites that thrived during the Maya Collapse period were in the regions that suffered the strongest droughts, whilst many sites that were abandoned were in regions rich in hydric resources. Explanations are reviewed for these contradictions. Finally, the works towards the development of mathematical models of the environmental variables are briefly reviewed, pointing out the lack of a proper computational model that has been fed by the palaeoclimatic data developed by the records in the MA.
... The environmental history of Mesoamérica; Oasisamérica and Aridoamérica, the historical cultural areas of the nowadays Mexican territory has been mainly studied focusing on the Maya Area (MA) (Douglas et al. 2015;Metcalfe et al. 2000;Torrescano-Valle & Islebe 2015). This interest is multifactorial, however, the Maya Collapse during the Epiclassic and its relationship with a series of Megadroughts is probably the main reason for this focus (Gill 2000;Haug et al. 2001;Webster et al. 2007). ...
... At the same time that the environmental history of the MA was studied, first from a paleoecological point of view in the last decades of the 20th century (Deevey 1977;Deevey et al. 1979;Vaughan et al. 1985;Wiseman 1985), and then from a predominantly paleohydroclimatic viewpoint in this century (Akers et al. 2016;Curtis et al. 1996;Hodell et al. 1995Hodell et al. , 2005aMedina-Elizalde et al. 2016a;Rosenmeier et al. 2002;Stansell et al. 2020;Webster et al. 2007), another topic on Earth Sciences was developed that focuses on the impact of the Saharan dust (Prospero et al. 1981). It was clear that the study of the distribution of Saharan dust was important for the desertification processes in Africa, both past and future (McGee et al. 2013;Mulitza et al. 2010). ...
... Any paleoenvironmental investigation would be incomplete without time series analysis, including wavelet and spectral analysis of the climate indicators studied (Trauth 2006). The application of these analyses to high resolution that these climate files possess, (Akers et al. 2016;Asmerom et al. 2012;Frappier et al. 2007Frappier et al. , 2014Medina-Elizalde et al. 2016b,a;Pollock et al. 2016;Smyth et al. 2011Smyth et al. , 2017Webster et al. 2007;Wiseman 1985), which could not be found in lake sediment archives. However, analytical scanning used for the analysis of chemical elements or elemental relationships using XRF or MS can change this. ...
Most paleoenvironmental studies indicate the presence of a water stress in the Maya Cultural Zone during the Epiclassic, the period when the Collapse of the Maya Civilization happened, supporting the Maya drought hypothesis. Both palaeoenvironmental studies and the archaeological record indicate that the consequences of and resilience to Mayan droughts were different in every subregion of the Maya Cultural Zone. One of the uncertainties in this scenario is related to the flourishing of Mayan populations during the times of the collapse in the Puuc region and the Cochuah region, whose water resources were (and are) generally scarce. The archaeological project of the Cochuah region indicates that the settlement of groups in this region existed during the time of the Epiclassic collapse, but lasted shortly thereafter. Additionally, palynological studies in Lake Chichancanab and Lake Esmeralda in the Cochuah Region indicate a low human impact that supports a relatively short period of population. Studies done in Chichancanab and Lake Esmeralda indicate severe droughts during the Maya Collapse. The present project aims to answer how these regions whose water resources were not particularly better than those of other regions within the Maya territory became flourishing regions during the years of the collapse, as well as to explain their relative short occupation using a unexplored environmental factor. This factor is the arrival of sand from the Sahara to the central portion of the Mayab, which would have returned or maintained productive soils, making the region resilient to the drought. In addition to this, the project focuses on two other issues relevant to the environmental history of these regions. One is the presence of organic matter in the numerous bodies of water in the North of the Mayab for ca. 4000 years BP. Which is incongruent with the low amount of population that existed in most of the time. And the second is the existence of a bimodal distribution in the isotopic signal of δ 18 O of shells of Hidrobiidae gastropods, which may mean a difference in the isotopic signal of water between the rainy and dry seasons. If this is true, the differences in the hydroclimatic cycle between the rains caused by the north and the summer rains could be reconstructed.
... Lake sediment records from the Petén region, Guatemala, record substantial changes in geochemical, magnetic, and biological variables in response to climate changes for at least the past 75,000 years Escobar et al., 2012). More recent and temporally resolved paleoclimate records, including evidence from speleothems, span the entirety of prehispanic Maya history and from European contact through to present (Webster et al., 2007;Medina-Elizalde et al., 2010, 2016aKennett et al., 2012;Douglas et al., 2015). Combined, geomorphic records exist for climate and water balance changes through the Holocene from multiple regions in the Maya lowlands. ...
... This drought phase took place during a dynamic and arguably tumultuous period in Maya history that saw the decline of many major Maya cities across the region (Webster, 2002), and led to the hypothesis of a 'Maya Collapse' by the 10th century CE Luzzadder-Beach et al., 2016). Paleoclimate records across the region suggest substantial, prolonged reduction in precipitation during this period (Hodell et al., 1995;Webster et al., 2007;Wahl et al., 2013;Douglas et al., 2015). A climatically driven explanation for the widespread societal shifts and settlement abandonment during this period remains a leading hypothesis in the geoscience and archeological communities. ...
... Some paleoclimate records also suggest drier conditions in the Early Postclassic and in the historic era, including during the Little Ice Age (Hodell et al., 2005;Medina-Elizalde et al., 2016a, b), superimposed on a long-term trend of Late Holocene drying (Wanner et al., 2008) (Fig. 3). (Hodell et al., 1995;Haug et al., 2001;Webster et al., 2007;Yaeger and Hodell, 2008;Medina-Elizalde et al., 2010, 2016aKennett et al., 2012;Douglas et al., 2015). Dry periods common across records and regions are shown in yellow highlight. ...
Prehispanic societies transformed large areas of tropical forest in Mexico and Central America, a region now known as the Maya lowlands, into highly engineered urban and agricultural landscapes, over a period of more than two millennia. This chapter provides an overview of the impacts of the ancient Maya on their environment, with a focus on the history of Maya modification of local and regional geomorphic systems during the late Holocene. An overview of the geomorphology of the Maya lowlands is provided, with key examples of Maya interactions with and modifications of the landscape. The Maya converted natural ecosystems into vast urban and rural infrastructure with locally attuned water management systems that included reservoirs, wetland fields and canals, terraces, field ridges and water temples. Evidence for increasing Maya deforestation, carried out for urbanization and agriculture, is preserved in the form of deep sequences of anthropogenic sediments that cascaded through catchments, buried Maya infrastructure and paleosols, silted in reservoirs, waterways, floodplains and wetlands, and accumulated on lake bottoms. The use of proxies for ancient Maya land-use intensity, such as inorganic and organic geochemistry and stable carbon isotopes, soil organic matter and mineral magnetism, are briefly reviewed. The Maya geomorphic impacts were sufficiently severe that centuries of erosion left a region-wide anthropogenic chronostratigraphic marker known as the ‘Maya Clay’ across much of the southern Maya lowlands. The greatest geomorphic impacts of the Maya in the region began to diminish by c. 1000 BP, in response to social and political upheavals that have been referred to as the ‘Maya Collapse.’ Geomorphological, geoarcheological, and paleoenvironmental investigations have provided data that can be used to quantify Maya-mediated environmental impacts and test hypotheses about climate and environmental drivers of societal ‘Collapse.’
... The percentage of titanium in the Cariaco marine record is also shown, indicating the movement of the ITCZ (Haugh et al., 2003), which is argued as the primary driven of humid conditions in the area, although the ITCZ does not reach the Maya Cultural Area entirely. The grey bands highlight the dry periods linked to the 4.2 and 2.5 Holocene Events (Mayewski et al., 2004) (Curtis et al., 1996, c) Aguada X'Caamal (Hodell et al., 2005), d) Speleothem at Rio Secreto (Medina-Elizalde et al., 2016), e) Speleothem at Box Tunich (Akers et al., 2019), f) Speleothem at Macal Chasm (Webster et al., 2007) and Speleothem at Yok Balum . The grey band highlight the dry period linked to the Maya Collapse (C), while the orange bands indicate climatic stress ( .9 ...
... (e. g. Gill et al., 2007;Haug et al., 2001;Hodell et al., 2005;Webster et al., 2007). ...
... Among scholars, it is common to define the Maya Cultural Area as a region that contains the modern Mexican states of Campeche, Quintana Roo and Yucatan, most of the Mexican state of Tabasco and the eastern part of the Mexican state of Chiapas, the countries of Guatemala, Belize, and partially the northern departments of Honduras and El Salvador (e. g. Phillips & Jones 2009, Webster et al. 2007). However, this definition is not entirely right, since there are regions belonging to the Zoque-Olmec and Nahua cultures in the area, which are clearly divergent from the Maya (Charles and George, 2010;Grube et al., 2012;McKillop, 2004;Phillips and Jones, 2009;Sabloff, 1994;Thompson, 1966;Wilhelmy, 1981). ...
The environmental history of the Maya attracts attention since climate changes appear to be linked with the management of resources and, in particular, with the collapse of their civilisation at the end of the Mesoamerican Classic period, (1140-1040 B. P), when, according to palaeorecords from the region, such as lake sediments and speleothems, a series of droughts occurred. However, attention has been focused mostly on the central lowlands and northern Mayab (but barely in the Highlands and other areas) where ca. seventy records have played an important role in our understanding of climate change and the role of drought in societal change, including the Maya Collapse. This includes some stable isotope records, in particular, δ18O from lake sediments and speleothems as proxies of water balance and precipitation amount, respectively. The most emblematic record comes from Lake Chichancanab, whose sediments contain gypsum deposits at specific points indicating the existence of droughts during crucial moments in Mayan history (e. g. The Maya Abandonment at 1200 years B. P. and the Maya Collapse from 1190 to 1040 B. P). In this thesis, research involves lake core sediments obtained both in the lowlands and the highlands.
First, an isotopic record on bulk carbonate for a site in the highlands (over 1000 m.a.s.l.) was obtained from a sediment core from Lake San Lorenzo in the Lagunas de Montebello Lake Complex. In addition, a density record was developed as well as a record based on the organics, carbonate, and residual content of the loss on ignition. Today, Lake San Lorenzo is hydrologically open. The isotope record δ18O in Lake San Lorenzo is a proxy of summer rainfall amount, indicating that the lake has always been hydrologically open. Episodes of major organic production appeared after periods when the surroundings were very densely populated, according to Franco Gaviria et al. (2018). Changes in the sedimentation rate through the record, including the abrupt change after 610 – 553 years B. P., as well as changes in the vegetation, are in part linked with changes in the summer rainfall amount but might also be driven by changes in the land use during the Colonial period.
Second, core sediments collected from Lake Esmeralda, a sister lake of Chichancanab, are studied in the lowlands. Isotopic analysis of waters and modern gastropods (family Hydrobiidae) from both lakes (Chichancanab and Esmeralda) were studied, showing that L. Esmeralda is today a more open basin in comparison to L. Chichancanab but still shows an important evaporative effect.
Samples for isotope analyses based on shells of gastropods (Pyrgophorus coronatus, family Hydrobiidae) from Holocene aged sediments from Lake Esmeralda were compared with the isotopic composition of samples of carbonate bulk sediment for assessing the quality of the environmental signal recovered from them. Overall both records should be very similar patterns. Therefore, a complete isotope record based on sieved sediment samples was used as a proxy of effective rainfall (water balance) in Lake Esmeralda (due to its lower cost).
Results based on a multiproxy approach (CaCO3 content, organic content, loss on ignition residuals content, the isotopic composition of bulk sediments, elemental abundance, elemental ratios, density, grey and colour scale) on a sediment core dated by radiocarbon suggest that Lake Esmeralda's sediments are predominantly made up of carbonates from 6500 to 3400 B. P. Lake Esmeralda became a more closed system, after ca. 4200 B. P. After 2500 B. P., there appears to be a further tendency to be a close system. Lake Esmeralda has become more organic-rich in the last 2500 years B. P. This coincides with periods when the human population across the Mayab turned to permanent settlement and developed urban centres. However, settlements (Shaw, 2000) and human impact on vegetation (Bermingham, 2020) near Lake Esmeralda existed practically only during the years of the Terminal Classic Horizon (950 years B. P.), suggesting an increase of the organics in the lake without major direct human disturbance. There is clear evidence for a dramatically increased organic amount in sediments from Lake Esmeralda, mostly produced outside the lake due to the loss of soil cover, during the critical moments of the Maya History, e. g. Maya Abandonment (1800 to 1750 years B. P.), the Maya Hiatus (1360 years B. P) and the Maya Collapse (1190 to 1040 years B. P.) at moments when the δ18O and the K/Sr show dry periods (at 1140 to 1040 years B. P.). No evidence of gypsum deposit was found before the drought at 167 years B. P., indicating a different catchment and chemistry of Lake Esmeralda compared to Chichancanab.
Finally, records of Lake Esmeralda and Lake San Lorenzo were compared, showing that in both lakes, the terrigenous intake is associated with the rainfall. But in Lake San Lorenzo, this process might also be linked with the erosion enhanced by the abandonment of agriculture. Besides, the CaCO3 precipitation is autogenic in both lakes, but such precipitation increases during dry periods in Lake San Lorenzo, whilst it decreases during dry periods in Lake Esmeralda. An opposite tendency in the hydrobalance at the millennial-scale to the lowlands happens in Lake San Lorenzo, in comparison to Lake Esmeralda. However, at decadal scale, the presence of recurrent droughts as it is registered in Esmeralda is still observed in San Lorenzo, indicating that the droughts during the critical moments of the Maya History were meteorological droughts.
... The Preclassic abandonment period (ca. 150-250 CE) was a time of political destabilisation that saw the abandonment of many mainland centres, closely chronologically linked with a multi-centennial scale drought (Medina-Elizalde et al., 2016;Webster et al., 2007). The Terminal Preclassic was not homogenous across mainland settlements, as coastal mainland sites such as Colha and Moho Cay became increasingly important (McKillop, 2010). ...
... The addition of Zea mays to the existing subsistence strategies may have been driven by the period of destabilisation (both climatic and political) associated with the Preclassic abandonment period. Direct evidence for this diversification during destabilisation is seen in the correlations between Zea mays cultivation in the dry forest, macrofossil evidence for maize consumption in the coastal settlement of Marco Gonzalez (Graham et al., 2017) and the aforementioned evidence for drought (Medina-Elizalde et al., 2016;Webster et al., 2007) (Fig. 5). As previous evidence has shown a strong marine based subsistence for inhabitants at Marco Gonzalez (Graham et al., 2017;Williams et al., 2009), the largest settlement on the island was likely impacted by the destabilisation, resulting in increasing exploitation of the dry forests. ...
... Following the collapse of the Classic Maya political system and the depopulation of some lowland centres (ca. 750-1000 CE), the Postclassic period saw the re-organisation of mainland communities in settlements along the coast and near water bodies (Cucina, 2015;Miller, 1985;Webster et al., 2007). As populations moved towards island and coastal locations, existing land-use strategies likely became more intensified at Basil Jones, explaining the heightened period of environmental change recorded. ...
Ancient Maya societies experienced a period of reorganisation and change in settlement patterns associated with social and climate instability at the end of the Classic period (750-1000 CE) and the subsequent Postclassic period (1200-1500 CE). Although it has been proposed that severe droughts and the breakdown of Classic political systems caused a migration of populations towards the coast, we have little evidence of the nature of land-use at coastal sites. Our understanding of subsistence on islands has been shaped by archaeological research indicating marine-based diets, with maize imported from the mainland. Here we provide, for the first time, palaeoecological proxy data that inform on ancient Maya land-use on an island site, located on Ambergris Caye, Belize. Using pollen and charcoal proxies, we present over 6000 years of environmental change and land-use history. Our reconstruction reveals evidence of cultivation, beginning at 2900 BCE and culminating during the Postclassic Period. We demonstrate that periods of higher land-use intensity correlate with climate instability, which corroborates archaeological evidence of migration to coastal locations. We hypothesize that the diverse marine and terrestrial environments of the island provided sustainable resources for the mainland Maya to use during times of both political and climatic stress.
... La intensidad de gris está asociada a la cantidad de detrito y materia orgánica presente al tiempo de la precipitación (p. ej : Webster et al., 2007;Boch et al., 2011), la cual a su vez depende también de condiciones climáticas al exterior de la cueva. De esta manera es posible construir una serie de tiempo a partir de las variaciones de color a lo largo del eje de crecimiento, la cual puede contener información vital de cambios en el ambiente arriba de la cueva. ...
... Se ha utilizado la escala de grises como indicador climático en estalagmitas con anterioridad, encontrándose que no había una respuesta clara en las señales obtenidas, de manera que no es posible distinguir entre calcita rica en detrito (pardo oscura) y calcita clara traslúcida, aun cuando ambas son creadas por diferente regímenes de humedad (Webster et al., 2007), distinción que en cambio, es posible distinguir por luminiscencia o utilizando una escala cromática con valores arbitrariamente elegidos. Otros trabajos han utilizado la escala de grises para indagar la naturaleza de la textura y el color, aunque no directamente como indicador paleoclimático (White, 1981;Perrette et al., 2005;Jex et al., 2008). ...
... Sin embargo se decidió trabajar con la serie de 2400 dpi para las futuras comparaciones, pues ésta contiene una mayor densidad de información (Figura 3). Los valores altos en la escala de grises corresponden con los tonos claros, donde existe calcita blanca porosa y los valores bajos corresponden con los tonos bajos donde existe calcita densa parda, llamada por algunos autores translúcida (Webster et al. 2007, Boch et al. 2010. ...
In this work we study stalagmite banding as an alternative proxy for paleohydrological conditions in stalagmites difficult to date using standard radiometric methods. A stalagmite cross-section is digitalized and the resulting matrix averaged, resulting on a high-resolution spatio-temporal record of tonality changes in the stalagmite. Assuming that the tone-change is due to the annual growth cycle, it is then possible to establish a relative geocronological framework to further study the stalagmite. Moreover, the high-resolution stable-isotope analysis of the stalagmite indicates that the grey-tone variability reflects changes in organic matter inputs from the epikarst to the stalagmite, whilst the distance between different bands is related to changes in the carbonate O-isotope composition, hence, rainfall amount.
... The Maya paleoenvironmental record derives from several lines of evidence, most prominently analyses of lake core sediments and more recently from studies of speleothems (Deevey et al., 1979;Binford et al., 1987;Jacob, 1995;Webster et al., 2007;Hodell et al., 2012;Douglas et al., 2016;Medina-Elizalde et al., 2016;Akers et al., 2019;Castro-López et al., 2021;Brenner, 2022;James et al., 2022). Vegetation changes across the Holocene (Figure 3) are recorded in the pollen register from these lake cores (Vaughan et al., 1985;Leyden, 2002), which are dominated by wind-borne pollen (Kellman and Tackaberry, 1997;Bradley, 1999). ...
... This is the case, despite the search for evidence of drought and other environmental impacts (Haug et al., 2003;Aimers and Hodell, 2011;Iannone et al., 2014). Based on the Cariaco core, precipitation was essentially stable, with some rise in levels of Ti, indicating increased rainfall (Haug et al., 2001), although research on speleothems has contributed to interpretations of drought (Webster et al., 2007;Ford 10.3389/fevo.2022.868660 FIGURE 4 Precipitation proxy and key pollen for the last four millennia in the Maya forest. ...
Human expansion into and occupation of the New World coincided with the great transition from the Pleistocene to the Holocene epoch, yet questions remain about how we detect human presence in the paleoecological record. In the Maya area of southern Mesoamerica, archeological evidence of the human imprint is largely invisible until ∼4,000 years ago. How do environmental changes after that time correspond and relate to human impacts? Are the archeological signatures of initial settlements in the Early Preclassic detected? Later, by ∼2,000 years ago when the Maya had fully settled the landscape, how does the evidence of forest compositional changes relate to human intervention? This paper evaluates published paleoecological data in light of the rise of the Maya civilization and reflects on interpretations of how swidden agriculture and the milpa cycle impacted the environment. Evaluating the contrast between the long archeological sequence of successful Maya development and paleoecological interpretations of destructive human-induced environmental impacts requires a concordance among pollen data, archeological evidence, ethnohistoric observations, ethnological studies of traditional Maya land use, and the historical ecology of the Maya forest today.
... Some records from Mexico, Puerto Rico and Panama indicate that the Spörer minimum was the coldest and/or driest period during the LIA Nyberg et al., 2002;Rodríguez-Ramírez et al., 2015) while others indicate the most severe conditions during the Maunder minimum (Black et al., 2007;Cuna et al., 2014). In Belize, according to stalagmite reconstruction, the LIA climate was relatively wet, with one short dry period at the end of the 15 th century (Webster et al., 2007). An similar scenario for the LIA has been determined using data from western Mexico (Rodríguez-Ramírez et al., 2015) that indicate relatively wet conditions persisting throughout most of the LIA with a short dry interval at the beginning and a slightly pronounced Maunder minimum. ...
... Lake Petén Itzá (Pérez et al., 2010); 15. Cave Macal Chasm (Webster et al., 2007); 16. Blue Hole (Gischler et al., 2008); 17. ...
Using a 530-year sediment record from the maar Lake Apastepeque, El Salvador, and based on diverse geochemical and biological (cladocerans, chironomids, diatoms, ostracods, testate amoebae) indicators, we estimated climatic and environmental alterations during the Little Ice Age (LIA) and reconstructed the recent history of the lake. Results demonstrate relatively humid conditions in the mid-elevations (500 m a.s.l.) of El Salvador during most parts of the LIA, resulting in high lake levels. Contrarily, the first part of the LIA was characterized by drier climates comparable to studies from Mexico and Belize, which correlated this phase with the Spörer minimum. Regional comparison with palaeorecords from the northern Neotropics reveals a high heterogeneity in local expressions of the LIA in Central America, likely connected to the high topographic heterogeneity of the region. Since the beginning of the 20 th century, Lake Apastepeque has experienced enhanced human impact expressed as increased nutrient supply. The most recent period was characterized by significant environmental disturbance, which we relate to an upper-crustal earthquake, one of the strongest over the last 500 years, that affected the region on 13 th February 2001 (Mw = 6.6, epicentre at 10 km depth, 30 km from the lake). The release of toxic bottom components such as hydrogen sulphide and high turbidity and turbulence of water caused major species turnover in the lake ecosystem, resulting in a massive fish kill and colonization by large cladocerans. Modern sediments still show slightly altered biota communities compared to pre-earthquake assemblages, indicating that the ecosystem has still not fully recovered.
... More stable drips or less participation of foreign particles and organic molecules will probably form columnar compact calcite, with shows fewer and smaller intercrystalline fluid inclusions. If the amount of drip changes seasonally or if it carries some impurities at the beginning or during the wet season (Baker et al. 2007;Webster et al. 2007), the annual growth layers ...
... The occurrence of micrite in stalagmites is usually related to very low discharge and condensed carbonate deposition (Frisia and Borsato 2010;Frisia et al. 2012), to the partial or total desiccation of the stalagmite surface (Frisia 2015) and even to depositional processes involving bacterial mediation (Frisia and Borsato 2010;Frisia 2015). Under these conditions, aerosols and cave dust particles may attach to the stalagmite surface (Webster et al. 2007;Dredge et al. 2013) and promote irregularities on the active growing surface of calcite crystals or facilitate the growth of microorganism communities. In both cases, the imperfect crystallization pathways may promote the singular morphology of boudin fluid inclusions. ...
Fluids trapped in speleothems have an enormous potential in frontier fields of paleoclimate and paleohydrological research. This potential is, however, hampered by diverse scientific and technical limitations, among which the lack of a systematic methodology for genetically characterizing fluid inclusions is a major one, as these can have different origins, and thus, the trapped fluid (usually water), different meanings. In this work, we propose a systematic petrological classification of fluid inclusions, based on: 1) the temporal relation between fluid inclusions and the host calcite, 2) the spatial relation between fluid inclusions and the “crystallites” and crystals aggregates, and 3) the phases (water, air) trapped inside fluid inclusions. The first criterion allows dividing fluid inclusions in two main categories: primary and secondary, whose identification is critical in any research based on trapped fluids. The other two criteria allow the definition of eight types of primary and four types of secondary fluid inclusions.
Primary fluid inclusions contain the drip water that fed stalagmites at the time of crystal growth, and can be intercrystalline, i.e., located between adjacent crystallites, or intracrystalline, i.e., with the fluid trapped within crystallites. We differentiate six main types among the intercrystalline fluid inclusions (elongate, thorn-shaped, down-arrow, interbranch, macro-elongate, and bucket) and other two among intracrystalline inclusions (pyriform and boudin). In primary inclusions, water is the main phase, while gas is much less abundant. The presence of gas could be related to slow drip rates or degassing in the cave, but also to later leakage due to changes in temperature and humidity often occurring during inadequate handling of speleothem samples.
Secondary fluid inclusions were clearly related to younger water inlet through stratigraphic disruptions or unconformities. They are formed after water infiltration, but sealed before the renewed crystal growth. We differentiate four main types of secondary inclusions: interconnected, rounded, triangular, and vertical fluid inclusions. The identification of primary and secondary fluid inclusions in speleothems is a key for interpretation in paleoclimate studies.
Integration of petrological results allow establishment of three different genetic scenarios for the formation of fluid inclusions, whose identification can be relevant because of their predictive character.
... The collapse of these centers was often a result of accumulating events involving environmental factors followed by increased conflict. Some of these environmental factors included significant droughts (Brenner et al. 2002;Dunning et al. 2014;Webster et al. 2007), environmental degradation (Beach et al. 2006;Sharer 2006), and the shrinking of water sources (Wahl, Byrne, and Lysanna 2014). There was also increased conflict and warfare, as seen through the construction of defensive walls, such as at Cival (Estrada-Belli 2011), and at Muralla de Leon (Rice and Rice 1981), and in the creation of fortifications, such as the dry-ditch and parapet at Becan (Webster 1976). ...
... There was significant variation among each of the cities regarding when they were abandoned and the causes leading to their collapse. Some of the most common causes included droughts (Webster et al. 2007), ecological collapse (Turner and Sabloff 2012), warfare (Inomata 1997), and internal conflicts (Folan et al. 2000;Sharer 2006). ...
This dissertation investigates the role of civic-ceremonial plazas in the formation and maintenance of the Preclassic period Maya centers of Cival, Holmul, and Witzna located in the Cival region in northern Guatemala. Ancient Maya public plazas are largely understudied by archaeologists, despite filling a critical role in the understanding of community formation and interaction through the practices associated with the commemorative and ceremonial rituals held in these locations. These public plazas were places of interaction that ranged from public, open places to restricted spaces. The theories of practice, structuration, place, social memory, and communities of practice are utilized here to critically examine the types of interactions and activities experienced in these plazas.
This examination of civic-ceremonial plazas in the Cival region draws upon excavations, GIS data, proxemics, estimated plaza capacity, and archaeological evidence of ritual activities to understand practices, which resulted in the emergence and continued occupation of public plazas. Lime plaster samples acquired from plaza floors are used to provide insight into the interaction and exchange of practices between the sites of Cival, Holmul, and Witzna. Thin section petrography, SEM-EDS, and x-ray fluorescence spectrometry (pXRF) are used to analyze the mineralogical and elemental composition of lime plaster, which is subsequently used to determine the quality of the plaster and in the identification of communities of practice.
Findings from this study confirm the strong connection between Cival and Holmul during the Late Preclassic period by demonstrating the existence of multiple communities of practice involving the addition of barite to lime plaster production and the semi-standardization of E-Groups in the region. Additionally, it was discovered that the centers of Cival, Holmul, and Witzna each experienced a distinct trajectory regarding the construction and spatial positioning of public and private plazas. Despite these differences, public plazas remained essential focal points of community activity and as locations for commemorative and ceremonial rituals for each of these three sites throughout the Preclassic and Classic periods. Private plazas were also essential locations for ceremonial and ritual events conducted among a more restricted community, such as seen at the Watchtower plaza in East Witzna. The practices associated with the ritual events in these plazas were preserved in the material remains of lime plaster surfaces, caches, and stelae. These physical remains are used to provide insight into the types of rituals conducted in these plazas.
... Hypotheses for the the collapse of the Maya can generally be separated into two categories: (i) socio-political, such as class conflict (Hamblin and Pitcher, 1980;Chase and Chase, 2005), inter-site warfare (Webster, 2000;Inomata, 2008), changes in trade routes (Demarest et al., 2014) or pathological ideological systems (Dornan, 2004;O'Mansky and Dunning, 2004); and (ii) environmentally related, which includes soil erosion (Beach and Dunning, 2006;Anselmetti et al., 2007), volcanic activity (Gill and Keating, 2002;Tankersley et al., 2011), deforestation (Oglesby et al., 2010;McNeil et al., 2010), diseases (Acuna-Soto et al., 2005) and climate change induced drought (Hodell et al., 2001;Haug et al., 2003;Hodell et al., 2005;Gill et al., 2007;Webster et al., 2007;Medina-Elizalde et al., 2010;Medina-Elizalde and Rohling, 2012;Kennett et al., 2012;Douglas et al., 2015). ...
... A fall in crop production is consistent with evidence from skeletal remains that show signs of progressive nutritional disease (Folan and Hyde, 1985;Sharer and Traxler, 2006), while at the same time, there are no mass graves discovered that might indicate large scale epidemics or warfare (Folan et al., 2000). Our research cannot be taken as proof, but it does suggest that drought, though important, played a smaller role than previously thought (Hodell et al., 2001;Haug et al., 2003;Gill et al., 2007;Webster et al., 2007;Kennett et al., 2012;Douglas et al., 2015). ...
The dynamics and structure of societies have long been a puzzle to archaeologists, historians and social scientists in general. In particular, increases in social inequality and the possibility of societal collapse are two deeply distressing prospects for any society. In this three paper thesis we provide two contributions to the literature of societal collapse and one regarding the emergence of social inequality.
In the first article we present a mathematical model of Easter Island and show that the collapse can be modelled as a supercritical Hopf bifurcation where the critical parameter is the harvesting rate of resources. This suggests an universal mechanism by which societal collapse can be understood quantitatively. In addition, we show that societies coupled together can be more robust against collapse, which means that, within a larger region of parameter space, a sustainable outcome can occur for both societies than in the case when the societies are isolated. In particular, if at least one society has a harvesting rate below the critical value, then collapse can be prevented for the entire system.
In the second article we build a dynamical system model of the Maya civilisation taking into account the main specialisations of the population: swidden and intensive agriculturalists, and monument builders. The archaeological record for population growth and monument construction is accurately reproduced, with the model calibration close to archaeologically determined values for the parameters. We show that if, after the year 550 CE, a significant part of each new generation moved from swidden to using intensive
agricultural methods, then this would explain the rapid population growth and the subsequent collapse. This conclusion is reached irrespective of the impact of drought. Furthermore, the model is shown to also undergo a supercritical Hopf bifurcation when the harvesting rate is high. An extensive sensitivity analysis indicates that the model predictions are robust under parameter changes, which means that the period around the year 550 CE played a key role in the collapse.
In the third article we address the issue of social inequality by considering games on networks. In contrast to large parts of the literature, we investigate for what network structure a system of linked agents can exhibit maximally rational strategic behaviour. The agent’s strategies are quantified through the quantal response equilibrium, and the network is optimised so that the strategies are as close as possible to the Nash equilibrium. Previous work has argued that a scale-free topology maximises system rationality.
In contrast, we show that a core-periphery structure emerges, where a small set of nodes enjoy higher degrees than the majority, which are leaf nodes. In symmetric games the difference in degrees between the two node types are stark, whereas in asymmetric games the difference is less notable.
Taken together, the different parts of this thesis highlight and explain dynamical and large-scale structural features in societies as seen throughout the history of the world. Thus, this work can help deepen our understanding of complex social phenomena.
... AD 830-1000) is known to have been characterized by drought too severe to be overcome by Classic infrastructure projects. These changes are thought to have led to a decline of the great Classic Maya centers (Gill et al., 2007;Douglas et al., 2015;Kennett et al., 2012;Shaw, 2003;Webster et al., 2007). ...
... The water infrastructure at some sites, such as Palenque and Copan, focused heavily on drainage and flood water control with elaborate aqueducts, dams, canals, and roads that were designed to get rid of water rather than to store it (Davis-Salazar, 2006;French, 2007French, , 2009). In addition, speleothem records, which provide more fine-tuned temporal periods (on the order of annual to multi-decadal intervals) than lake sediment cores, reveal that the end of the Classic period included not just episodes of drought, but also episodes of extremely wet conditions (Frappier et al., 2014;Medina-Elizalde and Rohling, 2012;Smyth et al., 2017;Webster et al., 2007). Our research at the site of Ucanal, in Petén, Guatemala, contributes to these more nuanced, regionally-specific perspectives to underscore the more varied nature of water infrastructure systems that include the problems of having too much water (Dunning and Houston, 2011;Smyth et al., 2017). ...
... of the Preclassic period are said to contribute to sociopolitical reorganization of this time (Carrillo-Bastos et al., 2010;Kennett et al., 2012;Douglas et al., 2015). Likewise, a series of droughts in the Terminal Classic coincides with abandonment of numerous large urban/civic centers (Hodell et al., 1995(Hodell et al., , 2001(Hodell et al., , 2005Haug et al., 2003;Webster et al., 2007;Medina-Elizalde et al., 2010). In low lying coastal plain areas where the water table floats on a sea water intrusion (Perry et al., 2003), rising Holocene sea level (Fairbanks, 1989;Lambeck and Chappell, 2001;Toscano and Mac-Intyre, 2003) pushed up groundwater levels and caused increased flooding and soil aggradation in wetlands (Alcala-Herrera et al., 1994;Pope et al., 1996;Beach et al., 2009). ...
... For example, at Punta Laguna in the northeastern Yucatan Peninsula (just south of the Yalahau region), alternating bands of organic-and carbonate-enriched strata were interpreted to reflect lower and higher lake stands, suggested to be a product of lesser and greater rainfall . Periods of lesser rainfall (droughts) in turn have been linked to Maya sociopolitical reorganization during the Late Preclassic (Carrillo-Bastos et al., 2010;Kennett et al., 2012;Douglas et al., 2015) as well as to the Terminal Classic collapse (Hodell et al., 1995(Hodell et al., , 2001Haug et al., 2003;Hodell et al., 2005Hodell et al., , 2007Webster et al., 2007;Medina-Elizalde et al., 2010). ...
The Yalahau region of northern Quintana Roo, Mexico, contains abundant freshwater wetlands and a history of Maya occupation that spans nearly 3000 years. The highest regional population levels occurred during the Late Preclassic period, from ca. 100 BC to AD 350/450. The Maya constructed rock alignments crossing wetland swales, and these have been hypothesized as features used to trap soil and water for production of food and useful biological resources such as periphyton. Paleoenvironmental studies from a wetland in the eastern part of the region suggested that occupation of the Yalahau region, and manipulation of the wetlands, corresponded to a period when the water table was lower than in modern times, creating wetland ecosystems that were most productive for cultivation. This paper presents results that apply this model at the regional scale (in wetlands in other parts of the region). Thirty short soil cores were collected from 12 wetlands across the region. For this project, 5 cores from 4 wetlands were selected for analyses including micromorphology and radiocarbon dating. Thin sections studied under petrographic microscope were used to identify the various types of features present in the core sequences including carbonates, organic matter, shell, pyrite, gypsum, and pore space. In each core, it was possible to distinguish an upper unit dominated by biogenic-micritic carbonate and a lower unit characterized by a variety of unique soil features such as sparitic calcite crystals, pyrite, gypsum, and gleyic properties. Based on this, it is suggested that while modern soil forming processes are fairly uniform across the region and controlled by regular annual flooding (~7 months of >1m deep flooding each year), in the past (Preclassic period), flooding was less regular and wetland environments were more swampy and varied. Furthermore, it is suggested that the Preclassic depressions encountered by the Maya were a prime agricultural resource that allowed the region to flourish during the Late Preclassic period. However, as flooding became more regular at the end of the Preclassic period, the region was abandoned, only to be reoccupied in the Late Postclassic when wetlands were exploited for aquatic resources rather than for agriculture.
... All were directed toward identifying general trends of environmental change and human impacts, including evidence of early forest removal for swidden agriculture and later deposition of thick, siliceous "Maya clay" resulting from heavy construction. These and related studies (e.g., of lowland speleothems; Webster et al., 2007) typically do not seek or discuss direct correlations with specific, dated, cultural events aside from climatic (drought) causes of the Late Classic southern lowland Maya "collapse" (e.g., Douglas et al., 2016;Dunning et al., 2012). ...
... Again, similar phenomena are evident in the Mirador Basin around 130-225 CE (Dunning et al., 2014, p. 120) and also elsewhere in the lowlands. These developments are associated with drier climatic conditions and a "Late Preclassic collapse"-cessation of monumental architecture and depopulation-of large sites such as El Mirador, Cuello, and others (see, e.g., Beach et al., 2015;Douglas et al., 2016;Dunning et al., 2012;Ebert et al., 2017;Inomata et al., 2017;Medina-Elizalde et al., 2016;Wahl et al., 2007;Webster et al., 2007). In the PI-1 core, the abrupt shift observed at 100 CE corresponds to another increase in Ca and Sr, further supporting correlations between Late Preclassic lowland site abandonments and aridity. ...
Sedimentological information obtained from lake sediment cores has long been used to show how the Maya impacted their environment. Although general trends are usually observed, direct correlation of construction, deforestation, and abandonment of cities is hindered by poor chronological correlation between sedimentary and archaeological data. We report on findings from a 515-cm core covering the last ~7000 years of sedimentation that displays remarkable correlation between the two. The core was extracted from Lake Petén Itzá (Department of El Petén, northern Guatemala) immediately adjacent to Nixtun-Ch'ich', a long-lived (ca. 1300 BCE–1750 CE) southern lowland Maya site. Chronological precision for the core was achieved by an age-depth model based on Bayesian statistics and corroborated by dates from archaeological excavations. This model, based on six radiocarbon dates and integrated with physical (magnetic susceptibility) properties and scanning XRF analysis of elemental (Si, Fe, and Ti; also Sr and Ca) constituents, permits exceptionally precise correlations with independently dated constructional activity at Nixtun-Ch'ich'. Erosion resulting from the Middle Preclassic (800 to 500 BCE) creation of the site's atypical urban gridded landscape is prominently registered in the core. Other sediment changes at the end of the Late Preclassic period (ca. 50–200 CE) may be drought-related and reflect local expression of a “Late Preclassic Maya collapse,” suggesting new avenues for archaeological exploration. This study highlights the potential of lake sediments, continuously recording human activities in the catchment, as faithful registers of subtleties unrecovered archaeologically. Detailed analyses of sediments deposited close to sites' drainage pathways may reveal intricate correlations such as those observed here, and shed light on cultural activities and environmental and living conditions undetected in the archaeological record.
... Our first idea was that gypsum is a relict feature related to more arid phases in the past. Dry periods occurring throughout the late Holocene in the Maya region are inferred from different proxies: lacustrine (Hodell et al., 2005;Leyden et al., 1996;Torrescano-Valle & Islebe, 2015), speleological (Medina-Elizade et al., 2010;Webster et al., 2007), and marine (Haug et al., 2003). The hypothesis of a drought (or series of droughts) as the main cause of the decline of southern Classic Maya communities has become dominant during the last decades. ...
The soil mantle of the tropical karstic landscapes of Southern Mexico was shaped by specific processes of pedogenesis and long‐term human impacts of ancient Maya agriculture. To understand the interaction between natural and human‐induced soil‐forming processes in the calcareous mountains of Chiapas state, we studied soil toposequences around the Classic Maya site of Budsilhá and related them to the archaeological evidence of settlement and land‐use distribution. Soil chemical analysis, micromorphological observations, and clay mineral identification were carried out in key soil profiles at the main geoforms. Limestone hills are occupied by shallow Rendolls which are usually perceived as incipient soils. However, high content of silicate clay composed of kaolinite and vermiculite and ferruginous clayey soil material observed at macro‐ and microscale backed the hypothesis that these soils were formed from the residues of thick Terra Rossa after their erosion. Swampy lowlands are occupied by thick clayey gleyic soils with clay mineral assemblages similar to those in the upland Rendolls. We suppose that the mineral matrix of the lowland soils is largely derived from the pedosediments of eroded upland Terra Rossa, which lost original ferruginous pigmentation and aggregation due to redoximorphic processes. Some wetland soils contain neoformed gypsum that is atypical for humid tropics; sulfide‐sulfate transformation under fluctuating redox conditions could promote gypsum synthesis. Ancient Maya land use was closely related to soil‐geomorphic conditions: settlements with homegardens occupied calcareous hills, whereas the primary agricultural domain was developed on lowland soils after their drainage by artificial canals.
... about C.E. 700 and continuing to 950, Mesoamerican cities experienced a tumultuous period. Teotihuacan erupted in civil strife and collapsed, Cacaxtla-Xochitecatl experienced significant eruptions from Popocatepetl and mudslides off Iztaccihuatl resulting in an exodus, and in the Maya lowlands, the urban centers, which had grown during the Early and Late Classic (e.g., Calakmul, Tikal, Caracol, etc.), experienced profound sociopolitical and economic changes generated variously by internal conflicts among elites, droughts, and/or military confrontations between polities, which caused abandonment, migration, and displacement of the population and the emergence of new regional powers, such as Uxmal and Chichen Itzáin the Terminal Classic (Blanton et al., 1993;Peterson and Haug, 2005;Sharer and Traxler, 2006;Webster et al., 2007;Medina-Elizalde et al., 2010;Serra Puche and Lazcano Arce, 2012;Mumary Farto, 2016). Thus, the period after C.E. 950 until the Spanish conquest (C.E. ...
The impact of ancient urban occupations on sustainability has recently become a topic of interest for archaeologists as well as many other scholars. Much of this archaeological research has focused on documenting the longevity of ancient cities and elucidating the social and economic strategies employed at the urban and regional scales to promote urban sustainability. In this article, we add to this discussion by addressing the issue of sustainability by considering the impact of environmental legacies left by ancient cities after their abandonment. Using a series of cases from pre-Hispanic Mesoamerica [OMYK (Coba), Kiuic, Lagunas de Yalahau, and Tlaxcallan], we show through ethnoecological and historical ecological research that in some cases pre-Hispanic people, living in urban zones, affected “intermediate” disturbances that increased biodiversity, biomass, and sustainability by creating second natures that have endured for centuries.
... Conversely, dense compact calcite suggests slow growth, low porosity, and minimal fluid inclusions (Frisia, 2015;Boch et al., 2011). Calcite density has also been shown to decrease during hiatuses (Webster et al., 2007). The presence of hiatuses provides insight into changes in the depositional environment that may include decreased drip water volumetric input, changes in cave ventilation, a rise in water table height, or migration of the drip site on the cave ceiling. ...
Stalagmites being prepared for paleoclimate analysis should typically be slabbed along the central growth axis. This is an important first step because it allows for the highest resolution of sampling with minimal over- or under-sampling of the growth layers. Further, stable isotope ratios and trace element concentrations along the central growth axis most closely record climate variability. Choosing how to slab to best expose the central growth axis for geochemical sampling is challenging based on external morphology alone. High-resolution X-ray computed tomography (XRCT) can provide the ability to discern the internal growth morphology of stalagmites non-destructively, inexpensively, and rapidly. These data can inform selection of optimal slabbing plane(s) and can help identify locations for preliminary U-series dating. We develop a conceptual screening model to assess rapidly the internal morphologies of uncut stalagmites. The specifics of screening the internal morphologies through XRCT scans include investigating the internal porosity of the sample, the number and size of voids and hiatuses, and the presence and absence of growth layers and growth axes. We demonstrate that XRCT scans capture the migration of center of growth in uncut stalagmites of both simple and complex internal morphologies. XRCT scanning facilitates the investigation of stalagmites with complex internal growth banding, opening up avenues to work on such samples when stalagmites with simpler internal morphologies are not available. Further, screening stalagmites for paleoclimate reconstructions using XRCT improves the sustainability of speleothem science by helping researchers select which stalagmites should be returned to caves without destructive slabbing, thereby minimizing impact on caves.
... "La coexistencia de los elementos naturales de un centro urbano con los valores económicos y sociales que sus individuos hacen de él y de los ecosistemas que lo rodean, soportan y sufren su actividad" (Díaz, 2014, p. 59). 2 Teniendo cómo referencia al colapso progresivo, durante las distintas etapas de la civilización Maya; Si bien los mayas son reconocidos por dejar un legado identitario y deferente con su medio ambiente (sobretodo en la gestión de un sano sistema de aguas de la lluvia en zonas que se infiltra en las cuevas, grutas y cenotes) la alta vulnerabilidad del ambiente ante fenómenos climatológicos ha decantado en largos periodos de sequía, fenómeno que contribuyó al incremento de conflictos bélicos y al abandono de varios asentamientos de esta cultura durante el periodo posclásico(Serrato et al., 2021;Arnauld et al.,2017; Lases-Hernández et al., 2018;Medina et al., 2016;Douglas et al., 2012;Wolfgang et al., 2000;Haug et al., 2003;Webster et al., 2007). ...
The hydro-social cycle of the northern zone of Quintana Roo is in a socio-ecological dilemma due to the configurations of urban, political, social, and environmental patterns of development that have emerged since 1960-2022.
Therefore, in order to satisfy the needs of all the users that live in the hydro-social cycle, it is heading towards a socio-environmental crisis composed of micro conflicts, struggles and latent and manifest conflicts, which develop in a plot of conflictive configuration. This phenomenon of ungovernability has undermined the implementation of land use planning and aquifer protection policies in the State of Quintana Roo, Mexico.
In this research, 6 types of conflicts that compose this conflictive configuration are studied in depth, besides participatory cartographies are made to illustrate in maps these concept of conflictive configuration of the hidrosocial cicle and characterize this conflictive configuration to contribute with political science approaches that can promote aspects of water security in karstic systems.
El ciclo hidrosocial de la zona norte de Quintana Roo se encuentra en un dilema socioecológico por las configuraciones del desarrollo urbano, politico, social, ambiental que se ha gestado desde 1960-2022.
Por lo que para satisfacerse las necesidades de todos los usuarios que habitan en el ciclo hidrosocial se decanta hacia una crisis socioambiental compuesto de micro conflictos, pugnas y conflictos latentes y manifiestos, los cuales se desarrollan en una trama de configuración conflictiva. Fenómeno de ingobernabilidad la cuál ha mermado la implementación de políticas de ordenamiento territorial y de protección al acuífero en el Estado de Quintana Roo, México.
En esta investigación se profundiza en 6 tipos de conflictos que componen a esta configuración conflictiva. Además que se realizan cartografías participativas para ilustrar en mapas a este concepto de la configuración conflictiva del ciclo hidrosocial y se caracteriza a esta configuración conflictiva; para aportar apuntes de ciencia política que puedan promover aspectos de la Seguridad Hídrica en sistemas kársticos.
... Steele, E.G. Reinhardt, F. Devos et al. Quaternary Science Reviews 310 (2023) 108117 level studies from the area (e.g., Carrillo-Bastos et al., 2010;Gischler and Storz, 2009;Khan et al., 2017;Metcalfe et al., 2000;Webster et al., 2007). The elemental geochemistry results from the DP indicate high porosity and OM content (high inc/coh), minimal input of weathering products (low Ti/K), and low phytoplankton productivity (low Si/Ti;Figs. 3 and 6;Lo et al., 2016;McNeill-Jewer et al., 2019;Peinerud, 2000). ...
Cave sediments along the eastern coast of the Yucatan Peninsula contain important records of paleoenvironmental change that have not been fully explored. Reconstructing environmental changes in Boca Paila lagoon reveals details about sea level, flooding of the Sian Ka'an Biosphere, and the timeline of occupation at Muyil, an important Classic Maya maritime trading site. Three sediment cores (BP1, BP2, and BP3) were collected from a cave system beneath Boca Paila lagoon in the Sian Ka'an Biosphere. Radiocarbon dating, geochemical (X-Ray Fluorescence Core Scanning, d13C, C/N), and microfossil (foraminifera, diatoms, pollen) analyses were performed. The combined results show three distinct phases of coastal evolution. Phase 1 (1157 BCE or earlier), an upland area with mangrove associate Conocarpus erectus, grasses, and ferns, is characterized by: organic-rich detrital peat; a relative absence of foraminifera and diatoms; organic geochemistry results within terrestrial ranges (d13C values of -28‰ to -26‰); and low Sr/Ca, Si/Ti, and Ti/K ratios. These indicate dry conditions at the karst surface. Phase 2 (1157 BCE - 312 CE), a shallow wetland, is represented by: an increase in weathering products (Ti/K) and diatom productivity (Si/Ti); more positive d13C values (-27‰ to -22‰) and decreasing C/N ratios; and increased marine foraminifera (e.g., Ammodiscus sp.). These indicate more open water conditions. Phase 3 (>312 CE), a wetland/lagoon environment, is characterized by: carbonate-rich marl; a greater diversity of foraminifera (Ammonia spp., Elphidium spp., Rosalina spp., and Bolivina spp.), diatoms (Cyclotella meneghiniana, Craticula spp., Amphora spp., Hyalosynedra laevigata, and Grammatophora spp.) and pollen (from mangroves, ferns, grasses, palms, and pine); increased Si/Ti and Sr/Ca values; and mixed marine and terrestrial organic geochemistry values (d13C values of -22‰ to -20‰). These indicate increased input of marine organic sediment during sea-level rise. Sea-level and climate records support the interpretation of a dry upper karst environment prior to ~1157 BCE, with sea-level rise forming shallow (<50 cm) wetlands by ~312 CE. Previous archaeological analysis estimates that the first settlers arrived at Muyil ~350 BCE, but that population expansion and construction of most structures occurred during the Postclassic (925-1550 CE). Sea-level rise would have been an important factor in the expansion of coastal settlements and trade routes; continued sea-level rise after ~312 CE allowed for the formation of deeper lagoons and channels connecting the coast to Muyil and other inland sites which would likely not have been navigable prior to the Early Classic period (250-600 CE) as they would be too shallow. This study highlights the impacts of environment on society, as well as the importance of karst cave systems for obtaining paleoenvironmental records.
... Sequences of calcretes, paleosols, karstic pedosediments and coastal deposits could play an important role as a Quaternary paleoecological archive of regional importance. At present the main inferences about the climatic history of Yucatan and adjacent areas rely mostly on the lacustrine (Leyden et al., 1996;Curtis et al., 1998;Rosenmeier et al., 2002) and speleothem (Webster et al., 2007;Medina-Elizalde et al., 2010) records and involve the proxies from the marine sediment cores taken in the Caribbean (especially in the Cariaco basin (Haug et al., 2001). Providing high chronological resolution, most of these records covers, however, rather short time intervals, mostly the Holocene and sometimes part of MIS 2/Late Wisconsin. ...
The Quaternary carbonatic deposits of the Cozumel Island are mainly reefs and calcarenites in which karstic features, red clayey paleosols and layers of calcretes provide a record of terrestrial paleoenvironments still poorly explored. A main section, Cantera Payo, and three complementary sections: Cantera Transversal, Aerolito and Chempita were studied. Besides field work, micromorphology, physicochemical and mineralogical analyses of soils and calcretes were done. C and O stable isotope analysis was also conducted in calcretes. The cyclicity of sedimentary, karstic and pedogenetic processes was established. The chronological frame was obtained through the correlation dated calcretes and coral samples from Yucatan Peninsula, with ages ranging between ~Marine Isotope Stage (MIS) 7 to MIS 1. Two paleo-karstic surfaces were identified, labeled as PK1 (older) and PK2 (younger). The PK1 surface showed multi-face karst features as collapse breccias, dissolution pits and pipes, and karstic pockets filled with lithified brown and red paleosols. The red paleosols exhibited abundant redoximorphic features. Clay mineralogy in paleosols and modern soil is similar, with vermiculite and minerals of the kaolinite group. We interpret they are the result of moderate weathering under a seasonal tropical climate like that of present-day conditions. PK1 is capped by a calcrete layer, whose age probably corresponds to the Marine Isotope Stage (MIS) 6 (164 a 135 ka). Therefore, the host rock and the karstification and pedogenetic processes should occur before (probable during MIS 7) The stable carbon isotope composition of this calcrete has a mean δ¹³C value of −10.40 ‰ that suggests the presence of a C3 plant cover. During the MIS 5, poorly cemented calcarenites accumulated in the island related to the sea level rise during this interglacial stage. This calcarenite level has less developed karstification and pedogenetic processes. Another laminar calcrete with root traces and septal alveolar structure is found on top of the studied sections formed in the MIS 5 and the transition to MIS 4. Its δ¹³C value ranges between −9.40 ‰ and − 10.27 ‰ also related to a C3 plant cover. In the period between MIS 4 and MIS 1, karst development and pedogenesis is observed on the island, evidenced by the formation of caves and reddish-brown soils.
... For example, in the preclassical phase, the Mayans had managed to survive two long-term droughts, which were estimated by the analysis of stalagmites from the Yucatán [142,143]. Furthermore, in the classical phase, the Mayans had to deal with eight severe droughts of 3-18 years in length between 750 and 1050 AD [144][145][146][147]. Data show that, in these periods, growth was stopped, but the important fact is that the Mayans were able to recover many times. ...
Environmental determinism is often used to explain past social collapses and to predict the future of modern human societies. We assess the availability of natural resources and the resulting carrying capacity (a basic concept of environmental determinism) through a toy model based on Hurst–Kolmogorov dynamics. We also highlight the role of social cohesion, and we evaluate it from an entropic viewpoint. Furthermore, we make the case that, when it comes to the demise of civilizations, while environmental influences may be in the mix, social dynamics is the main driver behind their decline and eventual collapse. We examine several prehistorical and historical cases of civilization collapse, the most characteristic being that of the Minoan civilization, whose disappearance c. 1100 BC has fostered several causative hypotheses. In general, we note that these hypotheses are based on catastrophic environmental causes, which nevertheless occurred a few hundred years before the collapse of Minoans. Specifically, around 1500 BC, Minoans managed to overpass many environmental adversities. As we have not found justified reasons based on the environmental determinism for when the collapse occurred (around 1100 BC), we hypothesize a possible transformation of the Minoans’ social structure as the cause of the collapse.
... Sequences of calcretes, paleosols, karstic pedosediments and coastal deposits could play an important role as a Quaternary paleoecological archive of regional importance. At present the main inferences about the climatic history of Yucatan and adjacent areas rely mostly on the lacustrine (Leyden et al., 1996;Curtis et al., 1998;Rosenmeier et al., 2002) and speleothem (Webster et al., 2007;Medina-Elizalde et al., 2010) records and involve the proxies from the marine sediment cores taken in the Caribbean (especially in the Cariaco basin (Haug et al., 2001). Providing high chronological resolution, most of these records covers, however, rather short time intervals, mostly the Holocene and sometimes part of MIS 2/Late Wisconsin. ...
The Quaternary carbonatic deposits of the Cozumel Island are mainly reefs and calcarenites in which karstic features, red clayey paleosols and layers of calcretes provide a record of terrestrial paleoenvironments still poorly explored. A main section, Cantera Payo, and three complementary sections: Cantera Transversal, Aerolito and Chempita were studied. Besides field work, micromorphology, physicochemical and mineralogical analyses of soils and calcretes were done. C and O stable isotope analysis was also conducted in calcretes. The cyclicity of sedimentary, karstic and pedogenetic processes was established. The chronological frame was obtained through the correlation dated calcretes and coral samples from Yucatan Peninsula, with ages ranging between ~Marine Isotope Stage (MIS) 7 to MIS 1. Two paleo-karstic surfaces were identified, labeled as PK1 (older) and PK2 (younger). The PK1 surface showed multi-face karst features as collapse breccias, dissolution pits and pipes, and karstic pockets filled with lithified brown and red paleosols. The red paleosols exhibited abundant redoximorphic features. Clay mineralogy in paleosols and modern soil is similar, with vermiculite and minerals of the kaolinite group. We interpret they are the result of moderate weathering under a seasonal tropical climate like that of present-day conditions. PK1 is capped by a calcrete layer, whose age probably corresponds to the Marine Isotope Stage (MIS) 6 (164 a 135 ka). Therefore, the host rock and the karstification and pedogenetic processes should occur before (probable during MIS 7) The stable carbon isotope composition of this calcrete has a mean δ13C value of −10.40 ‰ that suggests the presence of a C3 plant cover. During the MIS 5, poorly cemented calcarenites accumulated in the island related to the sea level rise during this interglacial stage. This calcarenite level has less developed karstification and pedogenetic processes. Another laminar calcrete with root traces and septal alveolar structure is found on top of the studied sections formed in the MIS 5 and the transition to MIS 4. Its δ13C value ranges between −9.40 ‰ and − 10.27 ‰ also related to a C3 plant cover. In the period between MIS 4 and MIS 1, karst development and pedogenesis is observed on the island, evidenced by the formation of caves and reddish-brown soils.
... This relationship is, however, not a simple one, as we will explore in this study. Climatological publications on the Maya droughts often discuss links between droughts and the disruption of Classic Maya society, without specifically suggesting agricultural collapse (2,14,15), by briefly noting the potential impact on food production or agriculture (4,(16)(17)(18) or by discussing only maize in relation to drought impact on ancient agriculture (19,20). Turning to the impact of droughts and associated famines suffered by the Maya during the Colonial period, Hoggarth and colleagues (21) use historic records to examine maize availability during droughts, while the only reference to other food plants used during droughts is a brief allusion to eating the bark of trees. ...
Significance
The disruption of Classic Maya society coincided with extended droughts, as suggested by numerous paleoclimatic studies. However, the role of drought in civil upheaval and demographic decline is complicated by the difficulty of linking relatively coarse estimates of meteorological drought with fine-scale plant processes that underpin agriculture. Our analysis of drought resistance across the historically documented, indigenous food plants of ethnographic Maya groups shows a broad range of foods gradually dwindling through droughts of increasing severity. This finding implies that short to moderate droughts could have caused agricultural disruption but not subsistence collapse. However, multiyear extreme drought is consistent with agricultural collapse and the specter of starvation, unless mitigated by food storage or trade from areas less affected by drought.
... Regional climate variability, together with local hydrologic conditions, is expressed in paleoclimate records across the Yucatan Peninsula from lake and cenote sediment cores (Hodell et al. 1995(Hodell et al. , 2005Leyden et al. 1996;Douglas et al. 2016b), Caribbean coastal cave deposits (Gabriel et al. 2009;van Hengstum et al. 2010;Collins et al. 2015), and speleothems (Webster et al. 2007;Medina-Elizalde et al. 2010;Kennett et al. 2012;Douglas et al. 2016b;Akers et al. 2016). These records differ in the timing and severity of recorded drought events, making it difficult to reconstruct past atmospheric circulation and raising the need for an integrated spatio-temporal rainfall record. ...
Epikarst estuary response to hydroclimate change remains poorly understood, despite the well-studied link between climate and karst groundwater aquifers. The influence of sea-level rise and coastal geomorphic change on these estuaries obscures climate signals, thus requiring careful development of paleoenvironmental histories to interpret the paleoclimate archives. We used foraminifera assemblages, carbon stable isotope ratios (δ ¹³ C) and carbon:nitrogen (C:N) mass ratios of organic matter in sediment cores to infer environmental changes over the past 5300 years in Celestun Lagoon, Yucatan, Mexico. Specimens (> 125 µm) from modern core top sediments revealed three assemblages: (1) a brackish mangrove assemblage of agglutinated Miliammina and Ammotium taxa and hyaline Haynesina (2) an inner-shelf marine assemblage of Bolivina , Hanzawaia , and Rosalina, and (3) a brackish assemblage dominated by Ammonia and Elphidium . Assemblages changed along the lagoon channel in response to changes in salinity and vegetation, i.e. seagrass and mangrove. In addition to these three foraminifera assemblages, lagoon sediments deposited since 5300 cal yr BP are comprised of two more assemblages, defined by Archaias and Laevipeneroplis, which indicate marine Thalassia seagrasses, and Trichohyalus, which indicates restricted inland mangrove ponds. Our data suggest that Celestun Lagoon displayed four phases of development: (1) an inland mangrove pond (5300 BP) (2) a shallow unprotected coastline with marine seagrass and barrier island initiation (4900 BP) (3) a protected brackish lagoon (3000 BP), and (4) a protected lagoon surrounded by mangroves (1700 BP). Stratigraphic (temporal) changes in core assemblages resemble spatial differences in communities across the modern lagoon, from the southern marine sector to the northern brackish region. Similar temporal patterns have been reported from other Yucatan Peninsula lagoons and from cenotes (Nichupte, Aktun Ha), suggesting a regional coastal response to sea level rise and climate change, including geomorphic controls (longshore drift) on lagoon salinity, as observed today. Holocene barrier island development progressively protected the northwest Yucatan Peninsula coastline, reducing mixing between seawater and rain-fed submarine groundwater discharge. Superimposed on this geomorphic signal, assemblage changes that are observed reflect the most severe regional wet and dry climate episodes, which coincide with paleoclimate records from lowland lake archives (Chichancanab, Salpeten). Our results emphasize the need to consider coastal geomorphic evolution when using epikarst estuary and lagoon sediment archives for paleoclimate reconstruction and provide evidence of hydroclimate changes on the Yucatan Peninsula.
... As such, several studies have suggested that stalagmite coloration may be correlated with growth rate. In particular, it has been suggested that lower calcite saturation during drip formation results in darker color and higher luminescence (Genty & Quinif, 1996;Webster et al., 2007;Vanghi et al., 2019), which has been indicated in annually laminated stalagmites which feature alternating light porous and dark compact layers representing fast and slow growth rates (Treble et al., 2005;Fairchild & Baker, 2012). ...
Because they can archive a variety of geochemical proxies and be precisely and accurately dated with the U-Th decay series chronometer, stalagmites are widely used for paleoclimate reconstructions. However, limitations in the use of this chronometer arise because U-Th dating is analytically time consuming, expensive, and requires a relatively large sample size. These limitations restrict the number of absolute dates usually obtained, which can result in significant uncertainties in the age model and inhibit the ability to archive high resolution records of environmental variability, particularly in those stalagmites where there are variations in growth rate not constrained by U-Th dates. Here, we explore the relationship between stalagmite color and growth rate. Consequently, we evaluate the use of a simple, practically non-destructive approach to model the age-depth relationship of stalagmites using the sample color to provide a continuous record of growth rate. The method was developed by comparing high-resolution color images with pre-determined U-Th dates along the growth axes of seven stalagmites. The obtained results suggest that prior to dating, a color-derived, continuous growth rate model may be used to identify important changes in growth rate which may aid in the determination of the most efficacious locations for U-Th dating. Further, continuous color-derived interpolations between U-Th derived dates may be superior to traditional linear interpolation methods. Such an approach has the potential to greatly improve a researcher’s ability to efficiently choose sampling locations for more precise, albeit laborious and costly, U-Th dating.
... Whether the shifts in the most frequently recorded dates reflect different strategies in agricultural scheduling, which may have been required as a consequence of climatic changes and variations in the length of the rainy season [76,107,108], is a question that cannot be answered with the data at hand, because the choice of relevant dates was likely affected by unknown variables, including the variety of maize cultivated, local environmental peculiarities, and idiosyncratic aspects of worldview and political ideology. The latter appear to have had a prominent role, promoting both tradition and innovation. ...
In the 1920s, during the first archaeological excavations at Uaxactún, Petén, Guatemala, an architectural complex named Group E was interpreted as an ancient Maya astronomical observatory, intended specifically for sighting the equinoctial and solstitial sunrises. In the following decades, a large number of architectural compounds with the same configuration have been found, most of them in the central lowlands of the Yucatan peninsula. The multiple hypotheses that have been proposed about the astronomical function of these complexes, commonly designated as E Groups, range from those attributing them a paramount role in astronomical observations to those that consider them merely allegorical or commemorative allusions to celestial cycles, without any observational use. This study, based on quantitative analyses of a reasonably large sample of alignment data, as well as on contextual evidence, shows that many of the previous hypotheses cannot be sustained. I argue that E Groups, although built primarily for ritual purposes, were astronomically functional, but also that they had no specific or particularly prominent role in astronomical observations. Their orientations belong to widespread alignment groups, mostly materialized in buildings of other types and explicable in terms of some fundamental concerns of the agriculturally-based Maya societies. I present the evidence demonstrating that the astronomical orientations initially embedded in E Groups, which represent the earliest standardized form of Maya monumental architecture and whose occurrence in practically all early cities in the central Yucatan peninsula attests to their socio-political significance, were later transferred to buildings and compounds of other types. Therefore, it is precisely the importance of the astronomically and cosmologically significant directions, first incorporated in E Groups, that allows us to understand some prominent aspects of ancient Maya architecture and urbanism.
... There are other examples to further support such arguments. The Maya and the Mesopotamian civilizations rose and dispersed at regional and millennial time scales (deMenocal 2001;Webster et al. 2007;Douglas et al. 2015), while the more recent Hohokam (Waters 2008;Purdue and Berger 2015) and Cahokia societies (Munoz et al. 2015), in Arizona and Mississippi respectively, rose and dispersed at more local, sub-basins scale at centennial time scale. In this paper, we restrict ourselves to the Indus and MRB case studies when viewing water-based societies through the lens of endogenous growth theory. ...
The challenge of sustainable development is enshrined in the ambitious 2030 Agenda for Sustainable Development of the United Nations. The 17 goals and its various targets are unique with water being one of the cross cutting themes. Taking examples of past water dependent societies in a comparative setting, this paper challenges the new field of Archaeo-hydrology in how it could contribute to the 2030 Agenda based on what can be learned from past and contemporary water dependent societies. We find that societies have coped with climate variability by diversifying both in occupation, livelihoods and use of space. Sharing the costs of coordinating such diversification requires inclusive institutions and technological innovations. Similar to technology, new social institutions emerge in response to a changing environment. However, in tandem, slow out-migration of people seems to go on, driven by better livelihood opportunities outside. If technological innovation and institutional evolution are not rapid enough, then migration seems to take over as the adaptive mechanism in response to environmental changes resulting in rapid dispersal. This means that migration from smaller, less endowed societies can be expected to be rapid, with repetitive cycles of abandonment and rehabilitation after each critical climate or adverse environment events. Consequently, more place based local innovations should be encouraged and local economies should be diversified to increase the resilience so that vulnerable societies may inherit favourable know-how for a sustainable future under changing climatic conditions.
... Therefore, our results indicate toxigenic blue-green algal blooms in two of the main reservoirs just prior to the time of abandonment in the mid-9 th century CE as a period of severe dryness set in. Similarly, a Planktothrix bloom occurred in the Temple Reservoir during the Late Preclassic, an earlier time period that also was plagued by droughts [30][31][32] . Microcystin toxins produced by Planktothrix and Microcystis can cause detrimental health effects even at extremely low concentrations (~ 2 nM), and are resistant to boiling 33 . ...
Understanding civilizations of the past and how they emerge and eventually falter is a primary research focus of archaeological investigations because these provocative data sets offer critical insights into long-term human behavior patterns, especially in regard to land use practices and sustainable environmental interactions. The ancient Maya serve as an intriguing example of this research focus, yet the details of their spectacular emergence in a tropical forest environment followed by their eventual demise have remained enigmatic. Tikal, one of the foremost of the ancient Maya cities, plays a central role in this discussion because of its sharp population decline followed by abandonment during the late 9th century CE. Our results, based on geochemical and molecular genetic assays on sediments from four of the main reservoirs, reveal that two of the largest reservoirs at Tikal, essential for the survival of the city during the dry seasons, were contaminated with high levels of mercury, phosphate and cyanobacteria known to produce deadly toxins. Our observations demonstrate severe pollution problems at a time when episodes of climatic aridity were prevalent. This combination of catastrophic events clearly threatened the sustainability of the city and likely contributed to its abandonment.
... This record indicated steady drying through the Late Preclassic to Early Classic, a wetter Classic, a drier Terminal Classic, and the highest intensity and longest duration dry episode from 101-1100 CE in the Early Postclassic ( Figure 13.2 ). Earlier stalagmite work by Webster et al. ( 2007 ) from Belize also indicated severe dry periods during the Late Preclassic and Late Classic through early Postclassic. These and the Chichancanab lake studies add the likelihood of a long, severe Early Postclassic drought to our consideration of Maya history. ...
... The Late Preclassic period (300 BCE-100 CE) through the Protoclassic period (100-400 CE) is one such period of disruption when many significant Southeastern Mesoamerican and lowland and highland Maya centers were abandoned or re-organized (Dunning et al., 2012;Hirth, 1988). Scholars have argued that the volcanic eruption of the Illopango Caldera in El Salvador (Mehringer Jr. et al., 2005), a period of intense droughts, (Dunning et al., 2012;Webster et al., 2007), or the disruptive influence of the central Mexican polity of Teotihuacan (Bove and Medrano, 2003;Braswell, 2003) may have triggered this period of collapse and reorganization. However, there is no agreed upon cause for this period of instability. ...
Built places hold great power to both shape and mold behavior and communicate meaningful narratives and ideas. Such narratives and meanings are encoded and reproduced via social acts of remembering and forgetting. This paper explores the ways that places are memorialized or forgotten after periods of social and political re-organization when groups of structures or whole sites are abandoned. Herein three memory strategies are emphasized: protecting places, citation of abandoned spaces, and abandonment as an act of forgetting, in order to provide tools for archaeologists discussing memory and abandonment. Each strategy is illustrated using archaeological case studies from the Late Preclassic (300 BCE-100 CE) to Late Classic (600-900 CE) in southeastern Mesoamerica.
... These depressions are lower than their surrounding area and produce variation in elevation in an otherwise flat region. The pocket bajos at Aventura are today seasonally inundated, but were likely wetter throughout various points in the past, as several drying periods have been recorded in the region (Carrillo-Bastos et al., 2010;Medina-Elizalde et al., 2010;Webster et al., 2007). The relationship between land and water was important to the ancient Maya for a multitude of reasons. ...
A holistic and relational approach to landscape amplifies understandings of the complexities of human–environment relationships. This article examines ecological and social aspects of landscape at the ancient Maya city of Aventura, Belize, in the context of relational ontologies. The city of Aventura is enmeshed with microenvironments known as pocket bajos, and I argue that pocket bajos defy categorization as natural or cultural. By exploring their spatial context, material content, and associated activities that create cosmological connections, I demonstrate that the pocket bajos were active social agents in the construction of the city and the maintenance of community. The relations that people living at Aventura established with pocket bajos highlight the interconnectedness of humans with the environment, and this approach avoids projecting current-day Western categories of nature and culture onto the past.
... Previous research examining the spatial patterns and mechanisms driving precipitation change across the Central American Isthmus over the past 2000 years have focused upon the impacts and timings of hydrological extremes including the Medieval Climate Anomaly (MCA) 950-1250 C.E. and Little Ice Age (LIA) 1400-1850 C.E. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and the transition between the two [21]. These changes in hydroclimate are reported to be primarily driven by the interactions of three climatic forces: (i) the position of the Inter Tropical Convergence Zone (ITCZ); (ii) the North Atlantic Oscillation; and (iii) the El Niño Southern Oscillation (ENSO) [22]. ...
The Central American Dry Corridor (CADC) is the most densely populated area of the Central American Isthmus and is subject to the greatest variability in precipitation between seasons. The vegetation of this region is composed of Dry Tropical Forests (DTF), which are suggested to be highly susceptible to variations in climate and anthropogenic development. This study examines the vulnerability of past DTF surrounding the Asese peninsula, Nicaragua to climatic and anthropogenic disturbances over the past c. 1200 years. Past vegetation, climate, burning, and animal abundance were reconstructed using proxy analysis of fossil pollen, diatoms, macroscopic charcoal, and Sporormiella. Results from this research suggest that DTF have been highly resilient to past climatic and anthropogenic perturbations. Changes in DTF structure and composition appear to be linked to the abundance and intensity of fire. Pre-Columbian anthropogenic impacts on DTF are not detected in the record; however, DTF taxa decline slightly after European contact (1522 C.E.). Overall the DTF for the Nicaraguan region of the CADC were found to be highly resilient to both climatic and anthropogenic disturbances, suggesting that this region will continue to be resilient in the face of future population expansion and climatic variation.
L’effondrement socio-politique et urbain des sociétés mayas classiques (250-1000 de notre ère) a eu ses causes dans l'histoire régionale, qu’il faut connaître par des approches émiques directes (direct insider information, Butzer K. et G. Endfield, 2012 : 3630). La recherche sur les grandes causalités climatiques du collapse de la période classique terminale (800-1000) s’accompagne d’un patient travail de restitution de processus à différentes échelles temporelles. Nous proposons, en outre, de distinguer trois échelles sociétales, celle des dynasties royales avec leurs institutions politiques, celle des villes, et celle de la population générale, échelles auxquelles l’effondrement s’est produit successivement selon des modalités et des causalités différentes. C'est dans ce cadre que nous explorons la chronologie paléo-climatique des sécheresses établies il y a maintenant une décennie, et toujours de mise à ce jour. Comment les sécheresses relativement normales des années 760 auraient-elles joué un rôle dans l'effondrement des dynasties royales au début du IXème siècle ? Quelles données avons-nous sur l'impact de la sécheresse, plus longue (820-870) et profonde, sur la désertion graduelle des villes ? Enfin, comment penser un possible effondrement démographique des sociétés mayas des basses terres durant la très longue sécheresse postclassique du XIème siècle ?
The paleoclimate archives of the tropics and marginal tropics from Mexico to southern Brazil and their interpretation are presented and critically discussed. The importance of Quaternary glaciations for climate reconstruction is particularly emphasized and related to Quaternary environmental changes in the Central and South American lowlands. Older glacier traces, often dated much too young, provide evidence of thermal and hygric climatic fluctuations since the early Quaternary that were much greater than the climatic changes of the last ice age. The maximum glaciation of the Little Ice Age occurred in the Southern Hemisphere around CE 1700, north of the equator around CE 1850. Cold phases are characterized by greater aridity in the lowlands. The orbital and solar influence on large and small climate variations is documented by many different paleoclimate archives. Terrestrial South American paleoclimate data are correlated predominantly with Arctic and less with Antarctic data. Climate modeling rarely considers the terrestrial paleoclimate data of the New World tropics. The extent to which climate influenced human cultures is discussed using Central America as an example and is further elaborated in Chap. 9.
We conducted compound‐specific stable hydrogen (δD) and carbon (δ ¹³ C) isotope analysis on n ‐alkanes from terrestrial leaf waxes preserved in a 10 000‐year sediment profile from Lago de las Morrenas 1 (9.4925° N, 83.4848° W, 3480 m), a glacial lake on the Chirripó massif of the Cordillera de Talamanca in Costa Rica. Our results demonstrate millennial‐scale variations in hydroclimate across the Holocene, with drier than average conditions in the highlands during the early Holocene, but with gradually increasing precipitation; mesic conditions during the middle Holocene with a gradual drying trend; and highly variable conditions during the late Holocene. This general pattern is punctuated by several centennial‐scale manifestations of global climate events, including dry conditions during the 8200, 5200 and 4200 cal a bp events and the Terminal Classic Drought (1200–850 cal a bp ). Our δ ¹³ C analyses demonstrate that carbon isotope signals are responding to changes in hydroclimate at the site and reinforce prior interpretations of a stable páramo plant community that established following deglaciation and persisted throughout the Holocene. The shifts in hydroclimate inferred from analyses of n ‐alkanes in Lago de las Morrenas 1 sediments show correspondence with charcoal records in multiple lakes, with fires most common during drier intervals.
Hydroclimate variability on multi-decadal timescales has been a prominent feature of the circum-Caribbean region over the common era, with marked dry intervals noted in particular for the period 800–950 CE coinciding with the Terminal Classic Period (the so-called Terminal Classic Drought: TCD) in Mesoamerica, and with the Little Ice Age from about 1500 to 1800 CE, linked to complex ocean-atmosphere interactions. Previous compilations of palaeoclimate reconstructions have revealed a clear precipitation dipole between northern and southern Mesoamerica over the common era, which is consistent with meteorological data and modelling experiments. However, patterns of variability elsewhere within the region are less well understood, although palaeoclimate records do point to spatial complexity. Here, we present a ∼sub-decadal-scale lake-sediment hydroclimate reconstruction based on ostracod-shell stable isotopes from Wallywash Great Pond, Jamaica, covering the past ∼1800 years, which fills a spatial gap in records for the region. Variations in δ¹⁸O values at this site are a proxy for changes in effective moisture and they reveal a marked wet phase over the Terminal Classic Period (TCP), suggesting that the precipitation dipole over northern and southern Mesoamerica may have an east to west component. This is supported by some previous studies, although additional sites are required from strategic localities within the region to confirm this. The Little Ice Age interval at Wallywash is drier than the TCP, although the signal is less clear than at some sites within the wider region, suggesting that regional complexity in hydroclimate has characterised this interval as well.
The collapse of the Maya civilization in the late 1st/early 2nd millennium CE has been attributed to multiple internal and external causes including overpopulation, increased warfare, and environmental deterioration. Yet the role hurricanes may have played in the fracturing of Maya socio-political networks, site abandonment, and cultural reconfiguration remains unexplored. Here we present a 2200 yearlong hurricane record developed from sediment recovered from a flooded cenote on the northeastern Yucatan peninsula. The sediment archive contains fine grain autogenic carbonate interspersed with anomalous deposits of coarse carbonate material that we interpret as evidence of local hurricane activity. This interpretation is supported by the correlation between the multi-decadal distribution of recent coarse beds and the temporal distribution of modern regional landfalling storms. In total, this record allows us to reconstruct the variable hurricane conditions impacting the northern lowland Maya during the Late Preclassic, Classic, and Postclassic Periods. Strikingly, persistent above-average hurricane frequency between ~ 700 and 1450 CE encompasses the Maya Terminal Classic Phase, the declines of Chichén Itza, Cobá, and subsequent rise and fall of the Mayapán Confederacy. This suggests that hurricanes may have posed an additional environmental stressor necessary of consideration when examining the Postclassic transformation of northern Maya polities.
The primary theoretical question addressed in this book focuses on the lingering concern of how the ancient Maya in the northern Petén Basin were able to sustain large populations in the midst of a tropical forest environment during the Late Classic period. This book asks how agricultural intensification was achieved and how essential resources, such as water and forest products, were managed in both upland areas and seasonal wetlands, or bajos. All of these activities were essential components of an initially sustainable land use strategy that eventually failed to meet the demands of an escalating population. This spiraling disconnect with sound ecological principles undoubtedly contributed to the Maya collapse. The book's findings provide insights that broaden the understanding of the rise of social complexity - the expansion of the political economy, specifically - and, in general terms, the trajectory of cultural evolution of the ancient Maya civilization.
The pre-Columbian colonization of the Caribbean is traditionally described as a series of migrations from coastal South America moving northward, island to island, as “stepping-stones.” As the southernmost island in the Antilles archipelago, just 90 miles off Venezuela, the island of Grenada is assumed to be the crucial first “step” in these migrations. However, too little archaeological data was available to substantiate this claim.
This dissertation project was designed to fill the gap. Using the Ideal Free Distribution (IFD), a heuristic from Human Behavioral Ecology, a predictive model was built to test areas of high-probability for early settlement on Grenada via an island-wide “radiocarbon survey” that collected artifactual, soil, and radiocarbon samples. Dated samples were refined via Bayesian methods and compared to ceramic evidence to place each site within an island-wide settlement chronology. Modern environmental data was then used to determine suitability rankings and common characteristics of settlement decisions.
At present, the results confirm site locations on Grenada followed a pattern consistent with the IFD, which not only allows prediction of previously undiscovered sites but also infers subsistence practices, ecological impacts, and certain cultural values. Grenada’s settlement chronology begins with an early, Archaic Age fisher-forager presence possibly as early as 3-4000 BC, in line with the “stepping-stone” hypothesis. However, Ceramic Age settlements (which appear in Puerto Rico and the northern Lesser Antilles by 500 BC) were not established until hundreds of years later than the northernmost islands, despite their origins in South America. This corroborates an emerging hypothesis that the southern Caribbean was largely skipped by the earliest waves of Ceramic peoples, perhaps because the social milieu and domesticated landscapes of the northern islands were more attractive.
Grenada's peak, pre-Columbian population occurred during a time of heightened climatic unpredictability (AD 750-900), with dramatic changes in material culture (including the appearance of rock art and new ceramic styles) that mimic similar occurrences in lowland South America. Using Resilience Theory as a guide, this research suggests the influx was likely the result of continued immigration from the mainland, probably the Guianas region (comprising modern Guyana, Suriname, French Guiana, and bordering regions of Venezuela and Brazil). This may also have been the route taken by later Cayo potters (“Island Caribs”) just prior to Spanish Contact.
When the French finally settled Grenada in 1649, they reported two distinct indigenous groups—“Caraïbe” and “Galibis.” The Caraïbe were living in villages that had been continuously occupied since the earliest ceramic groups (AD 200-300), and it is argued that they were still making Suazan Troumassoid pottery. The Galibis, on the other hand, were living in sites that align with the arrival of Cayo pottery elsewhere, ~AD 1250. These sites indeed contain Cayo ceramic types.
Ultimately, this dissertation lays the baseline for more intensive studies. Now that we know where 87 of the sites are, their general character, and their general chronological placement, more targeted investigations driven by more specific types of questions can be researched.
Urbanization is a phenomenon that brings into focus a range of topics of broad interest to scholars. It is one of the central, enduring interests of anthropological archaeology. Because urbanization is a transformational process, it changes the relationships between social and cultural variables such as demography, economy, politics, and ideology. As one of a handful of cases in the ancient world where cities developed independently, Mesoamerica should play a major role in the global, comparative analysis of first-generation cities and urbanism in general. Yet most research focuses on later manifestations of urbanism in Mesoamerica, thereby perpetuating the fallacy that Mesoamerican cities developed relatively late in comparison to urban centers in the rest of the world. This volume presents new data, case studies, and models for approaching the subject of early Mesoamerican cities. It demonstrates how the study of urbanism in Mesoamerica, and all ancient civilizations, is entering a new and dynamic phase of scholarship.
New compound-specific isotope analyses of a sediment core from Laguna Los Mangos in southern Pacific Costa Rica improves understanding of late-Holocene precipitation change in a region with limited paleoprecipitation records that is vulnerable to future climate change. We established paleoprecipitation and paleovegetation records from compound-specific stable hydrogen and carbon isotopic compositions of terrestrially-derived n-alkanes (δ²Halkane and δ¹³Calkane) to assess paleohydrologic variability and potential linkages to paleoecological change and human activity as revealed by prior analyses of the Los Mangos core. The δ²Halkane values were corrected for isotopic fractionation using pollen counts from the same core. The Los Mangos record extends to 4200 cal yr BP and small increases in δ¹³C values of C29, +0.6‰, and C31 alkanes, +0.3‰, (δ¹³CC29, 31) indicate a slight increase in C4 vegetation after initial introduction of maize agriculture to the watershed at ca. 3360 cal yr BP. This slight increase in C4 vegetation is followed by the largest positive carbon isotope excursions in the record, as compared to record averages (δ¹³CC29 = +3.2‰, δ¹³CC31 = +5.0‰). Paleohydrologic variability likely influenced vegetation and human activity at Los Mangos. Lake desiccation during the late-Terminal Classic Drought (TCD) resulted in a sedimentary hiatus in the Los Mangos record from ca. 950 to 450 cal yr BP. Positive excursions in comparison to record averages occur for both δ²HC29 and δ²HC31 proxies (δ²HC29 = +25.3 to +13.4‰ and δ²HC31 = +6.5‰) during the middle Little Ice Age (LIA) and indicate drier than average conditions, but there is no evidence of desiccation during this period. Thus, drought conditions during the LIA were apparently not as severe at Los Mangos as during the TCD, possibly because of differing forcing mechanisms for LIA climate that originated, or were more clearly expressed, in the Atlantic basin.
Las múltiples hipótesis propuestas sobre la función astronómica de los grupos E en la arquitectura maya van desde las que les atribuyen un papel primordial en las observaciones astronómicas hasta las que los consideran meras alusiones alegóricas a ciclos celestes. Basándome en los análisis cuantitativos de los datos sobre los alineamientos medidos en diversos sitios, así como en evidencias contextuales, argumento que los grupos E eran astronómicamente funcionales, pero no tenían un papel específico o particularmente prominente en observaciones astronómicas. También muestro que las orientaciones plasmadas inicialmente en los grupos E –que representan la forma estandarizada más antigua de la arquitectura monumental maya y cuya presencia en prácticamente todas las ciudades tempranas en la parte central de la península de Yucatán atestigua su significado sociopolítico– fueron posteriormente transferidas a edificios y conjuntos de otro tipo. Por lo tanto, es precisamente la importancia de las direcciones astronómica y cosmológicamente significativas, primero incorporadas en los grupos E, la que nos permite comprender algunos aspectos sobresalientes de la arquitectura y el urbanismo de los mayas.
Significance
The Tierra Blanca Joven eruption of Ilopango occurred during Maya times but the exact timing and its impact have been controversial. It was thought to be responsible for the anomalously cold decade experienced in the Northern Hemisphere centered at 540 CE, but this date is at odds with archeological evidence that suggests a date near the start of the Early Classic Period (pre-450 CE). Our precise age of 431 ± 2 CE allows us to pinpoint the eruption in proxy records and shows that its impact was apparently limited. It appears to have only had major effects on populations within ∼80 km of the volcano, where the regions were blanketed by decimeters of ash fallout and pyroclastic density currents.
The climatic controls on the stable carbon isotopic composition (d13C) of speleothem carbonate are less often discussed in the scientific literature in contrast to the frequently used stable oxygen isotopes. Various local processes influence speleothem d13C values and confident and detailed interpretations of this proxy are often complex. A better understanding of speleothem d13C values is critical to improving the amount of information that can be gained from existing and future records. This contribution aims to disentangle the various processes governing speleothem d13C values and assess their relative importance. Using a large data set of previously published records we examine the spatial imprint of climate-related processes in speleothem d13C values deposited post-1900 CE, a period during which global temperature and climate data is readily available. Additionally, we investigate the causes for differences in average d13C values and growth rate under identical climatic conditions by analysing pairs of contemporaneously deposited speleothems from the same caves. This approach allows to focus on carbonate dissolution and fractionation processes during carbonate precipitation, which we evaluate using existing geochemical models. Our analysis of a large global data set of records reveals evidence for a temperature control, likely driven by vegetation and soil processes, on d13C values in recently deposited speleothems. Moreover, data-model intercomparison shows that calcite precipitation occurring along water flow paths prior to reaching the top of the speleothem can explain the wide d13C range observed for concurrently deposited samples from the same cave. We demonstrate that using the combined information of contemporaneously growing speleothems is a powerful tool to decipher controls on d13C values ...
The climatic controls on the stable carbon isotopic composition (δ¹³C) of speleothem carbonate are less often discussed in the scientific literature in contrast to the frequently used stable oxygen isotopes. Various local processes influence speleothem δ¹³C values and confident and detailed interpretations of this proxy are often complex. A better understanding of speleothem δ¹³C values is critical to improving the amount of information that can be gained from existing and future records. This contribution aims to disentangle the various processes governing speleothem δ¹³C values and assess their relative importance. Using a large data set of previously published records we examine the spatial imprint of climate-related processes in speleothem δ¹³C values deposited post-1900 CE, a period during which global temperature and climate data is readily available. Additionally, we investigate the causes for differences in average δ¹³C values and growth rate under identical climatic conditions by analysing pairs of contemporaneously deposited speleothems from the same caves. This approach allows to focus on carbonate dissolution and fractionation processes during carbonate precipitation, which we evaluate using existing geochemical models. Our analysis of a large global data set of records reveals evidence for a temperature control, likely driven by vegetation and soil processes, on δ¹³C values in recently deposited speleothems. Moreover, data-model intercomparison shows that calcite precipitation occurring along water flow paths prior to reaching the top of the speleothem can explain the wide δ¹³C range observed for concurrently deposited samples from the same cave. We demonstrate that using the combined information of contemporaneously growing speleothems is a powerful tool to decipher controls on δ¹³C values, which facilitates a more detailed discussion of speleothem δ¹³C values as a proxy for climate conditions and local soil-karst processes.
An examination of several historical texts in the Maya codices reveals that droughts were a significant concern to the pre-Columbian Maya that ultimately resulted in the collapse of their civilization. The effects of such droughts mentioned in those texts include damage to crops, famine, and wildfires. The dates assigned to five droughts in the codical texts agree with dates obtained from the analysis of lacustrine cores and stalagmites in caves by climatologists.
The excess Pb-210 dating method was applied to two young straw stalactites collected from a cave in southern Okinawa Island, Japan. The Pb-210 profiles only in the matrix of the straws exhibited an exponential decrease with distance from the tip. The Pb-210 profiles of th, two straw samples gave the values of 2.2 and 5.9 mm/y for longitudinal growth rates. The excess Pb-210 is distributed uniformly over the outer and inner surfaces of the straws. Such an excess of Pb-210 is presumably produced from the airborne Rn-222 which exists with high concentrations in the cave air and the ground water running through the central channel of the straws. During growing process of the straws, a part of the Pb-210 will be adsorbed on the tip of straw, and they are supposed to be incorporated into matrix part during reprecipitation of CaCO3.
When illuminated by ultraviolet light, many calcite speleothems (stalagmites, stalactites, flowstones) display luminescence caused by the presence of organic (humic) substances occluded in the calcite. The amplitude of luminescence varies in a banded pattern parallel to growth layering. Through 14C and thermal ionization mass spectrometry uranium-series dating, we show that cyclical oscillations in the luminescence have periodicities ranging from a few days to >=105 yr. A well-defined annual cycle is present in many vadose-zone speleothems and can be used to define the chronology of short-term events. This cycle is probably a response to hydrological events in the recharge to the cave. Longer term oscillations are inferred to be controlled by climate, through its effect on organic activity in the overlying soil.
THE Maya civilization developed around 3,000 years ago in Mesoamerica,
and after flourishing during the so-called Classic period, it collapsed
around 750-900 AD1. It has been specula
ted2-6 that climate change may have played a part in
this collapse. But efforts to reconstruct the last three millennia of
Mesoamerican climate using palynological methods have met with equivocal
success, because human-mediated deforestation has altered regional
vegetation in ways that mimic climate shifts, making it difficult to
discriminate between natural and anthropogenic
changes7-15. Here we use temporal variations in oxygen
isotope and sediment composition in a 4.9-m sediment core from Lake
Chichancanab, Mexico, to reconstruct a continuous record of Holocene
climate change for the central Yucatan peninsula. The interval between
1,300 and 1,100 yr BP (AD 800-1,000) was the driest of the middle
to late Holocene epoch, and coincided with the collapse of Classic Maya
civilization. This continuous climate proxy record thus provides
evidence of climate deterioration in the Maya region during the terminal
Classic period.
Cave deposits have been widely used as proxy recorders in deciphering palaeoclimate during the last glacial/interglacial maxima (approximately 120 ka) [Harmon et al., 1975; Atkinson et al., 1978; Goede and Harmon, 1983; Ayliffe and Veeh, 1989]. Palaeoclimatic studies of cave deposits for the past 1-1000 yr time scale require a precise dating technique, that until now has been lacking. Due to the multiple sources of carbon in speleothems, C-14 dates obtained for recently deposited calcite are highly variable and thus, C-14 dating techniques are not suitable to obtain speleothem ages for the past 1-1000 years.
Here, we show for the first time that speleothems contain high concentrations of excess Pb-210 and that this Pb-210 excess can be successfully employed to obtain growth rates of speleothems deposited during the last 100 years. Of two specimens analyzed, a tubular ''soda straw'' stalactite yielded a longitudinal growth rate of 1.1 mm/yr, while a normal icicle-shaped stalactite had a lateral growth rate of 0.028 mm/yr. The mass growth rates of these two speleothems (149 and 78 mg/yr respectively) are comparable within a factor of two. Studies of fine-scale variations in the isotopic composition of recent speleothems will help to corroborate the validity of palaeoclimate records obtained using longer lived isotopes and extending back into Pleistocene.
To investigate the climatic controls on the stable isotope composition of surface waters from Panama, we measured d 18 O and dD on river and lake waters collected from throughout the isthmus. We statistically analyzed the isotope data using correlation (nZ162 samples) and multiple stepwise regression (nZ148 samples). Variables are d 18 O, dD, deuterium-excess (d x), latitude, longitude, sample elevation, stream head elevation, median stream elevation above sample site, distance from the Caribbean, stream length above sampling site, estimated mean annual precipitation, and pH. Rainfall isotope data from Panama City were analyzed for temporal variability. Temporally, rainfall d 18 O values are negatively correlated with precipitation amount. Spatially, surface water d 18 O values decrease with distance from the Caribbean, an indication of progressive rainout as air masses traverse the isthmus. The Panama surface water line is defined as dDZ ð7:6G0:09Þ !d 18 OC ð10:1G0:6Þ, statistically identical to that from Costa Rica. Respective Panama meteoric water lines based on monthly and annual data are dDZ ð7:4G0:07Þ !d 18 OC ð5:5G0:3Þ, and dDZ ð8:2G0:60Þ !d 18 OC ð10:6G3:3Þ. We conclude that the dominant control on rain and surface water d 18 O values associated with the Central American monsoon are temporal and spatial amount effects. Surface water d 18 O values also show significant correlations with drainage basin parameters such as median and stream head elevation, and latitude and longitude. An equation derived from stepwise multiple regression relates d 18 O values to various physical parameters and explains 74‰ of the observed isotopic variation. Weaker correlations were found between deuterium excess and physiographic variables. Our results support the use of spatial sampling of surface waters for use as a rainfall d 18 O proxy, and will benefit ongoing paleoclimatic research in humid tropical regions. q 2005 Elsevier B.V. All rights reserved.
The South American Summer Monsoon (SASM) is a prominent feature of summertime climate over South America and has been identified
in a number of paleoclimatic records from across the continent, including records based on stable isotopes. The relationship
between the stable isotopic composition of precipitation and interannual variations in monsoon strength, however, has received
little attention so far. Here we investigate how variations in the intensity of the SASM influence δ18O in precipitation based on both observational data and Atmospheric General Circulation Model (AGCM) simulations. An index
of vertical wind shear over the SASM entrance (low level) and exit (upper level) region over the western equatorial Atlantic
is used to define interannual variations in summer monsoon strength. This index is closely correlated with variations in deep
convection over tropical and subtropical South America during the mature stage of the SASM. Observational data from the International
Atomic Energy Agency-Global Network of Isotopes in Precipitation (IAEA-GNIP) and from tropical ice cores show a significant
negative association between δ18O and SASM strength over the Amazon basin, SE South America and the central Andes. The more depleted stable isotopic values
during intense monsoon seasons are consistent with the so-called ’‘amount effect‘’, often observed in tropical regions. In
many locations, however, our results indicate that the moisture transport history and the degree of rainout upstream may be
more important factors explaining interannual variations in δ18O. In many locations the stable isotopic composition is closely related to El Niño-Southern Oscillation (ENSO), even though
the moisture source is located over the tropical Atlantic and precipitation is the result of the southward expansion and intensification
of the SASM during austral summer. ENSO induces significant atmospheric circulation anomalies over tropical South America,
which affect both SASM precipitation and δ18O variability. Therefore many regions show a weakened relationship between SASM and δ18O, once the SASM signal is decomposed into its ENSO-, and non-ENSO-related variance.
Modern complex societies exhibit marked resilience to interannual-to- decadal droughts, but cultural responses to multidecadal-to-multicentury
droughts can only be addressed by integrating detailed archaeological and paleoclimatic records. Four case studies drawn from
New and Old World civilizations document societal responses to prolonged drought, including population dislocations, urban
abandonment, and state collapse. Further study of past cultural adaptations to persistent climate change may provide valuable
perspective on possible responses of modern societies to future climate change.
The El Nino/Southern Oscillation (ENSO) system is a prominent component of interannual climate variability, and the Southern Oscillation Index (SOI) is a primary measure of the state of the ENSO system ([1][1]). Here, we present evidence that ENSO-related changes in the terrestrial carbon cycle can
In the anoxic Cariaco Basin of the southern Caribbean, the bulk titanium content of undisturbed sediment reflects variations
in riverine input and the hydrological cycle over northern tropical South America. A seasonally resolved record of titanium
shows that the collapse of Maya civilization in the Terminal Classic Period occurred during an extended regional dry period,
punctuated by more intense multiyear droughts centered at approximately 810, 860, and 910 A.D. These new data suggest that
a century-scale decline in rainfall put a general strain on resources in the region, which was then exacerbated by abrupt
drought events, contributing to the social stresses that led to the Maya demise.
Prehispanic water management in the Maya Lowlands emphasized collection and storage rather than the canalization and diversion
accentuated in highland Mexico. Reexamination of site maps of the ancient Maya city of Tikal, Guatemala, has revealed an important,
overlooked factor in Maya centralization and urban settlement organization. In a geographical zone affected by an extended
dry season and away from permanent water sources, large, well-planned reservoirs provided resource control as well as political
leverage.
This innovative study argues that the collapse of Classic Maya civilization was driven by catastrophic drought. Between A.D. 800 and 1000, unrelenting drought killed millions of Maya people with famine and thirst and initiated a cascade of internal collapses that destroyed their civilization. Linking global, regional, and local climate change, the author explores how atmospheric processes, volcanism, ocean currents, and other natural forces combined to create the dry climate that pried apart the highly complex civilization in the tropical Maya Lowlands in the ninth and tenth centuries.
Drawing on knowledge of other prehistoric and historic droughts, The Great Maya Droughts is a useful study of the relationship of humans to their natural and physical environment. The author tries to understand why the Classic Maya failed to adjust their behavior and culture to the climatic conditions and why civilizations in general sometimes collapse in the face of radical environmental change.
Upper Cretaceous and Tertiary sediments cover more than half of Guatemala and were deposited in the Chapayal basin, an extension of the Gulf Coast embayment. The basin's foredeep lies between a southern borderland and the Yucatan foreland. Deposition in the Caribbean was connected during late Mesozoic and early Cenozoic time with the deposition in the Chapayal basin by the Sarstun portal. The first age-identifiable sediments are the Carboniferous and Permian. The earliest Gulf Coast embayment deposition in the Chapayal basin was probably that of the late Jurassic Todos Santos Formation, followed by the thick Lower Cretaceous carbonates and evaporites of the Coban Formation. Overlying the Coban, the Upper Cretaceous units--which have an aggregate thickness of approximately 1,750 meters--include Senonian limestones of the Campur Formation and younger clastics of the Verapaz group. The latter consists of the Chemal, Sepur, and Lacandon Formations deposited in early episodic Laramide stages, with the Chemal and Sepur in the foredeep region and the Lacandon on the foreland. The Chemal and Sepur are an argillaceous facies, but the Chemal was deposited only in the region of the present-day Cuchumatanes Mountains and is preserved under distinct environmental conditions in synclinal and downfaulted valleys at elevations exceeding 10,000 feet. The shelfal Lacandon Formation is detrital limestone. Five early Tertiary and six late Tertiary formations occur in the Chapayal basin and Amatique embayment, and cover more than one-third of Guatemala. Previously, only the Rio Dulce and Toledo have been mentioned formally in the literature. The Sepur, thought by Sapper (1937) to be Eocene, is now known to be Cretaceous at the type locality and in other areas. The early Tertiary formations are assigned to the lower Eocene Peten Group. They were deposited contemporaneously and are differentiated on lithology and basin position. The Reforma, Cambio, and Toledo are the shaly formations in the foredeep region. The Toledo occurs only in the Amatique embayment. Shales with conglomeratic lenses characterize the Cambio, and softer clay shales identify the Reforma. The shelfal formations are the anta Amelia and Buena Vista, defined separately by an extensive basal gypsum bed in the overlying Buena Vista. Carbonates and evaporites occur in both formations, but evaporites predominate in the Buena End_Page 425------------------------------ Vista. The thickness of the Peten Group is 1,500 meters. Mid-Tertiary non-deposition divided Tertiary sedimentation into early and late periods. Late Tertiary sedimentation is represented by Oligocene to Pliocene deposits in the Chapayal basin and by Miocene to Pliocene(?) deposits in the Amatique embayment. The Chapayal basin formations are the Desempeno conglomerate, the Lacantun, and the Caribe which have an aggregate thickness of 1,500 meters of terrestrial and deltaic claystones, sandstones, and conglomerates. The Amatique embayment is a graben continuation of the Bartlett trough. The Miocene Rio Dulce Limestone is its oldest late Tertiary formation. Following late Miocene uplift, clastics of the Pliocene(?) Herreria and Armas Formations were laid down. The Rio Dulce has a thickness in excess of 1,000 meters, the Herreria 240 meters, and the Armas 2,500 meters. The seas withdrew at the end of the Pliocene. Quaternary depo its mask older rocks in some areas.
People usually study the chronologies of archaeological sites and geological sequences using many different kinds of evidence, taking into account calibrated radiocarbon dates, other dating methods and stratigraphic information. Many individual case studies demonstrate the value of using statistical methods to combine these different types of information. I have developed a computer program, OxCal, running under Windows 3.1 (for IBM PCs), that will perform both 14 C calibration and calculate what extra information can be gained from stratigraphic evidence. The program can perform automatic wiggle matches and calculate probability distributions for samples in sequences and phases. The program is written in C++ and uses Bayesian statistics and Gibbs sampling for the calculations. The program is very easy to use, both for simple calibration and complex site analysis, and will produce graphical output from virtually any printer.
An objective methodology, based upon the rank-ordering and spatial patterning of Maya centers of the central Peten and central Yucatan zones, is used to infer developmental sequencing in the Maya Lowlands. If courtyard counts are employed as the basic measure of center importance, the Tikal and Calakmul regions each exhibit a size continuum of centers, consistent with the rank-size rule. The Rio Bec and Chenes regions exhibit a size distribution characterized by the existence of several large centers of nearly the same size, i.e., a situation of pluralism. These findings suggest that at the end of the Classic period, Tikal and Calakmul were dominant centers in economically mature regions, with a balance between external and internal growth forces. On the other hand, the later Rio Bec and Chenes centers appear to be in a state of growth redistribution or decline, their external ties truncated by the collapse to the south. Spatial patterning is less conclusive and suggests a relatively dispersed pattern of centers in all regions. The overall conclusion, especially from the frequency distributions of centers by size, is that the "periphery" (exemplified by Rio Bec-Chenes) developed first, reached a period of stasis, and developed further only on the collapse of the "core" centers (Tikal-Calakmul).
Recent advances in the precision and accuracy of the optical techniques required to measure luminescence permit the nondestructive analysis of solid geologic samples such as speleothems (secondary carbonate deposits in caves). In this paper we show that measurement of speleothem luminescence demonstrates a strong relationship between the excitation and emission wavelengths and both the extent of soil humification and mean annual rainfall. Raw peat with blanket bog vegetation has the highest humification and highest luminescence excitation and emission matrix wavelengths, because of the higher proportion of high-molecular-weight organic acids in these soils. Brown ranker and rendzina soils with dry grassland and woodland cover have the lowest wavelengths. Detailed analysis of one site where an annually laminated stalagmite has been deposited over the past 70 yr during a period with instrumental climate records and no vegetation change suggests that more subtle variations in luminescence emission wavelength correlate best with mean annual rainfall, although there is a lag of ˜10 yr. These results are used to interpret soil humification and climate change from a 130 ka speleothem at an upland site in Yorkshire, England. These data provide a new continuous terrestrial record of climate and environmental change for northwestern Europe and suggest the presence of significant variations in wetness and vegetation within interglacial and interstadial periods.
In the past, marine sedimentologists have been unable to quantitatively investigate modern sediment accumulation on continental shelves, but recent development of Pb-210 geochronology provides a tool to overcome this limitation. It is used in this study to examine the accumulation of modern Columbia River sediments on the Washington continental shelf.Pb-210 profiles in Washington shelf sediments reveal three characteristic regions: a homogeneous surface layer (about 10 cm thick) where sediments are actively mixed by physical and biological processes, a region where Pb-210 activities decrease logarithmically with depth in the sediment, and a lower region of background activities. The surface mixed layer generally reflects erosion by wave and current activity in inner shelf sediments (shallower than about 60 m), and biological mixing in mid and outer shelf sediments. The region of logarithmic activities (i.e., radioactive decay) in the Pb-210 profiles provides the rate of sediment accumulation, which is on the order of mm/yr. The predominant depositional feature is a mid-shelf silt deposit in which accumulation rates progressively decrease north-northwestward away from the Columbia River.These results are consistent with other sedimentological observations, and indicate that Pb-210 geochronology not only allows determination of modern sediment accumulation rates, but also provides additional insight into processes affecting accumulation. Pb-210 geochronology can be an important sedimentological tool for future studies of continental shelf sedimentation in areas undergoing modern sediment accumulation.
Data on the Isotopic composition of yearly and monthly precipitation samples collected at various altitudes on Mount Cameroon, Africa, and in two transects from the Amazon to the Altiplano in Bolivia, South America, are presented. In Bolivia, the 2H/1H and 18O/16O ratios show seasonal variations, with lower values in the summer rainy months with respects to the winter dry ones. The δ2H and δ18O values are linearly correlated with a slope of 7.5 in all seasons, but the intercept is higher in winter than in summer.The δ-gradient vs. altitude is larger in rainy periods. The isotopic data are fitted by using a numerical model based on Rayleigh adiabatic condensation process. Model simulations show that the δ–altitude relationship slightly deviates from linearity, because the slope increases with altitude due to the lowering of temperature and the consequent increase of the condensation rate of atmospheric vapour. The parameters which most affect the shape of δ–altitude relationships are the temperature vertical gradient (lapse rate) and the initial relative humidity of the ascending air masses, while a change of the initial isotopic composition of water vapour determines a shift of the curve along the δ-axis. In addition, the model explains the observed increase of the deuterium excess with altitude.
A speleothem isotopic record taken from Jerusalem is used to reconstruct
regional climate over the last 170,000 years. Glacial periods in
Jerusalem were generally cooler and wetter than the present climate.
Stage 5e in the desert margin of Jerusalem was extremely unstable, dry,
and warm, and instability persisted throughout the transition to glacial
conditions. The climate after stage 5e became gradually cooler and
wetter over a 20,000-year interval and did not recover to interglacial
conditions in stages 5c and 5a. The δ13C varied by up
to 12‰, from glacial (stages 6, 4, 3, 2) values of -10 to
-12‰ that reflect dense C3 vegetation above the
studied cave, and up to 0‰ in early stage 5 when there was
probably complete loss of vegetation. The climatic instability during
interglacial periods is much larger than during glacial periods, and
glacial/interglacial transitions do not behave the same in each climatic
cycle in this region.
Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network ``Isotopes in Precipitation'' and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is controlled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical-maritime air mass originating in the northern Pacific, (4) equatorial-maritime air mass originating in the western equatorial Pacific, and (5) equatorial-maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain-out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of delta18O and delta2H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June-September) is depleted in 18O by more than 60/00 with respect to winter rainfall, despite of 10°C higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average delta18O of rainfall, which in the south of China (Haikou, Hong Kong) is about 2.50/00 more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation observed in some areas of the studied region result from a complete reversal of atmospheric circulation over these areas and changing source of atmospheric moisture. High d-excess values observed at Tokyo and Pohang during winter (15-250/00) result from interaction of dry air masses from the northern Asian continent passing the Sea of Japan and the China Sea and picking up moisture under reduced relative humidity. The isotopic composition of precipitation also provides information about the maximum extent of the ITCZ on the continent during summer.
The temperature variation of the fractionation of oxygen in exchange reactions between dissolved carbonate and water and between calcite and water and calculated on theoretical grounds, and checked experimentally. In the course of the experiments it was necessary to investigate several methods of decomposing calcium carbonate to carbon dioxide for mass spectrometer analysis. A method was developed for growing calcium carbonate from solution with the same isotopic composition as the carbonate shells of organisms produced at the same temperature from water of the same isotopic composition, and the results of these experiments at various temperatures are expressed in an equation relating the temperature of formation with the isotopic composition of the calcium carbonate and of the water.
We have developed techniques to measure the 23°Th abundance in corals by isotope dilution mass spectrometry. This, coupled with our previous development of mass spectrometric techniques for 234U and 232Th measurement, has allowed us to reduce significantly the analytical errors in 23~U_ 234U-230Th dating and greatly reduce the sample size. We show that 6 × l0 s atoms of Z3°Th can be measured to ± 30%~ (2o) and 2 × 10 l° atoms of 23°Th to ± 2%e. The time over which useful age data on corals can be obtained ranges from a few years to - 500 ky. The uncertainty in age, based on analytical errors, is ±5 y (20) for a 180 year old coral (3 g), ±44 y at 8294 years and +1.1 ky at 123.1 ky (250 mg of coral). We also report 232Th concentrations in corals (0.083-1.57 pmol/g) that are more than two orders of magnitude lower than previous values. Ages with high analytical precision were determined for several corals that grew during high sea level stands - 120 ky ago. These ages lie specifically within or slightly postdate the Milankovitch insolation high at 128 ky and support the idea that the dominant cause of Pleistocene climate change is Milankovitch forcing.
Selective chemical separation techniques for isotopic analysis of coexisting calcite, dolomite, siderite and magnesite have been investigated in this study. Comparison of reaction rates of all pure carbonate minerals with 100% phosphoric acid at 25° and 50°C demonstrated that a uniformly fine grain size (<200 mesh) is required. Tests with fine-grained (<200 mesh) pure calcite, dolomite, siderite and magnesite reacted at 25°C (calcite) and 50°C (others) show that δ18O of evolved CO2 increases during the course of reaction. This is probably due to a slight kinetic isotope effect associated with rapid dissolution of sub-micrometer carbonate crystallites adhered to the outer surfaces of the very fine-grained crystals. Isotopic analysis of carbonates based on CO2 from incomplete acid reactions is accurate only after minimum reaction times. Conversely, much longer reaction times than the minima are not required.Experiments conducted on variable mixtures of calcite-dolomite, dolomite-siderite and calcite-dolomite-siderite demonstrated the magnitudes of cross-contamination on the inferred isotopic compositions of the individual minerals. The isotopic compositions and magnitudes of their uncertainty can be evaluated for individual carbonates selectively extracted from natural mixtures by variable time-temperature protocol.
This paper discusses the factors controlling the variations of heavy isotope contents of 57 rain events collected throughout the rain forest regions of Cameroon, Central Africa, during the great rainy season (August–November) of 1994. Our data display a wide range of values, from +1.69 to −10.80‰ for 18O and from +23.2 to −85.5‰ for 2H. The data follow closely the global meteoric water line suggesting that rain formation processes occurred under isotopic equilibrium conditions between both the condensate and the corresponding vapour. This also indicates that the observed heavy isotope contents have not been altered by evaporation during the descent of raindrops to the ground.The low heavy-isotope contents observed for some precipitation events are assumed to be controlled by the amount of rainfall and/or by the low condensation temperature. The former effect is related to the northward passage of the intertropical convergence zone (ITCZ) over the region under study, whereas the second effect is linked to high altitudes of condensation. Moreover, the latitudinal variations of the weighted mean 18O contents indicates that in coastal areas (0–230 km inland from the Atlantic coast) the stable isotopic compositions of precipitation are controlled by a continuous extraction from the atmospheric reservoir of vapour as rains according to the Rayleigh distillation model, whereas at distances >230 km, recycling of continental moisture is thought to have influenced the isotopic compositions of rains.
Submerged sink holes and cave systems associated with oceanic limestone platforms often contain speleothems and dripstone
features which formed during subaerial exposure during glacially lowered sea level. A large stalactite, collected from a 50
meter deep terrace within the “Blue Hole” on Lighthouse Reef, offshore from Belize, records the geochronology of the transition
from subaerial exposure to marine submergence during Holocene sea level rise. The stalactite originally formed on the ceiling
of a large cavern when sea level was at least 60 meters below its present stand. As sea level rose, flooding the cavern, the
fresh water phase of dripstone formation terminated and a 12 cm-thick rind of botryoidal splays of radial-fibrous marine aragonite
coated the stalactite. This is the most massive encrustation of Holocene marine cement known, and it precipitated from seawater
which had been considerably modified during circulation through the carbonate platform. By approximately 3000 yBP, when sea
water flooded the bank top, cement accretion had ended, and the complex speleothem was encrusted by a marine biolithite prior
to falling to the mud-covered floor of the cavern.
The effects of different modes of formation on the isotopic composition of speleothems has been examined to delineate the conditions under which they may be used to give palaeo-climatic data. The modes of deposition considered were: equilibrium loss of CO2, kinetic loss of CO2, and evaporation of water.If isotopic equilibrium is maintained between HCO3− and CO2(aq) the calcite precipitated will be in isotopic equilibrium with the water and variations in will depend on climate alone, variations in will be independent of climate. This will occur if the loss of CO2 from solution is slow. If loss of CO2 is rapid a kinetic fractionation will occur between HCO3− and CO2(aq) and the calcite precipitated will show a simultaneous enrichment in 13C and 18O. If evaporation of water occurs the calcite precipitated will be enriched in 18O and will be close to 13C and 14C equilibrium with the cave atmosphere. Speleothems deposited under conditions of kinetic loss of CO2 or evaporation of water cannot be used to give palaeoclimate data.
We have developed techniques by sector-field inductively coupled plasma mass spectrometry (ICP-MS) for measuring the isotopic composition and concentration of uranium and thorium, focusing on the rare isotopes, 230Th and 234U. These isotopes have been widely used as tracers in earth sciences, e.g., chronology, paleoclimatology, archeology, hydrology, geochemistry, and oceanography. Measurements made on reference materials demonstrate that the analytical precision approximates counting statistics and that the accuracy of the measurement is within error of accepted values. Routine measurement times are 20 min for U and 10 min for Th. The sensitivities (ions counted/atoms introduced) are 2–3‰ for U and 1.5–2‰ for Th. Samples of 10–40 ng of 238U (0.5–2.0 pg of 234U) give measurement precisions of 1–2‰ (2σ) for δ234U and U concentration ([U]). Only 0.4 pg of 230Th are needed to achieve [230Th] and 230Th/232Th data with errors less than 5‰ even for cases where 230Th/232Th is 10−5 or less. Our ICP-MS data, including uranium standards, thorium standards, 238U–234U–230Th–232Th dating of speleothems and 230Th–232Th in oceanic particulates, replicates measurements made by thermal ionization mass spectrometry (TIMS). Compared to TIMS, the ICP-MS method allows smaller sample size and higher sample throughput due to higher sensitivity, fewer sample preparation steps and shorter measurement times. However, mass biases, intensity biases, spectral interferences and instrumental blanks are significant and must be addressed.
The stable isotope composition of equatorial high-altitude precipitation and surface-water bodies has been studied on Mt. Kenya (0°10′S; 37°20′E) in East Africa during July 1997. Regarding the local hydrology, glacier meltwater was identified as the main source of replenishment for the lakes, while direct precipitation and runoff appear to have a negligible contribution during this period of the year. Two through-flow lakes exhibit nearly no evaporative isotopic enrichment relative to the inflow isotopic composition, while two longer residence-time lakes display an oxygen and hydrogen isotopic build-up of 4.0–7.0‰ and 18.0–34.0‰, respectively. The data indicate that stream waters are composed of a mixture of high-altitude glacier meltwater and rainfall. The isotopic composition of an ice-sample obtained directly from the margin of a glacier is enriched relative to the average composition of the glacier, suggesting mixing with local rain. Samples of ground-frost crystals have an isotopic composition similar to the rain or slightly enriched. In addition, the results show the lack of a significant “altitude effect” on the mountain. This study demonstrates the importance of the characterization of local hydrological settings when interpreting lacustrine equatorial isotopic records of past climate and confirms that for East Africa, the total range in oxygen and hydrogen isotopic composition of meteoric waters is smaller than in high-latitudes.
We have re-determined the and half-lives to be 245,250±490 years (2σ) and 75,690±230 years (2σ), respectively. Using high precision thermal ionization mass spectrometric (TIMS) methods, we measured and atomic ratios in 4 different materials that were likely to have behaved as closed systems for 106 years or more: zircons with concordant , , and ages, Iceland Spar, Table Mountain Latite, and aliquots of a solution of Harwell uraninite (HU-1). We calibrated the TIMS multipliers using U-500, U and Th gravimetric standards, and U double spike. Consistent values for all measured materials and consistent values for all materials with the exception of our HU-1 solution support the secular equilibrium status. The new half-lives agree within error with previously determined values; however, errors in our values are generally smaller than those in the earlier determinations. Our half-life is about 3‰ higher than that commonly used in dating laboratories and our half-life is about 4‰ higher. ages calculated with the new half-lives are generally older than those calculated with the previously used half-lives. The difference in age, though, is small throughout the age range because our revised and half-lives are offset from earlier values in the same sense (both to higher values). In the case of dating materials older than 350 ka in laboratories that rely solely on gravimetric standardization procedures, use of our decay constants and their associated errors will considerably reduce the errors in age arising from uncertainty in the decay constants.
A 4000-yr sediment core record from Lake Salpetén, Guatemala, provides evidence for Maya-induced forest clearance and consequent soil erosion between ∼1700 cal yr B.C. and 850 cal yr A.D. Radiocarbon ages of wood, seeds, and charcoal support an age-depth model with average errors of ±110 cal yr. Relatively low carbonate δ18O values between 1300 and 400 cal yr B.C. coincide with pollen evidence for forest loss, consistent with increased surface and groundwater flow to the lake. Minimum δ18O values between 400 cal yr B.C. and 150 cal yr A.D. suggest a high lake level, as do 14C-dated aquatic gastropods as much as 7.5 m above the present lake stage. High lake levels resulted from reduced evaporation-to-precipitation ratios, increased hydrologic input caused by anthropogenic deforestation, or both. The Preclassic abandonment (150 A.D.) and Early Classic/Late Classic boundary (550 A.D.) are marked by relatively high δ18O values indicating reduced lake levels. Oxygen isotope composition increased further coincident with the Terminal Classic Maya demographic decline between 800 and 900 A.D. This period of high δ18O may have been caused by the greater aridity that has been documented in northern Yucatán lakes or by decreased hydrologic input to the lake as a consequence of forest recovery. Reduced soil erosion after 850 cal yr A.D. coincided with the Terminal Classic Maya demographic decline and permitted forest recovery and resumption of organic sedimentation.