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The Medieval Climate Anomaly in South America
Abstract
The Medieval Climate Anomaly (MCA) is a climatic perturbation with a core period of 1000-1200 AD that is
well-recognized in the Northern Hemisphere (NH). Its existence in the Southern Hemisphere (SH) and the level
of synchronicity with the NH is still a matter of debate. Here we present a palaeotemperature synthesis for South
America encompassing the past 1500 years based on multiproxy data from 76 published land and marine sites.
The data sets have been thoroughly graphically correlated and the MCA trends palaeoclimatologically mapped.
The vast majority of all South American land sites suggest a warm MCA. Andean vegetation zones moved upslope,
glaciers retreated, biological productivity in high altitude lakes increased, the duration of cold season ice
cover on Andean lakes shortened, and trees produced thicker annual rings. Similar MCA warming occurred in
coastal seas, except in the year-round upwelling zones of Peru, northern Chile and Cabo Frio (Brazil) where
upwelling processes intensified during the MCA due to changes in winds and ocean currents. MCA warming in
South America and the NH appears to have occurred largely synchronous, probably reaching comparable intensities.
Future studies will have to address major MCA data gaps that still exist outside the Andes in the central and
eastern parts of the continent. The most likely key drivers for the medieval climate change are multi-centennial
Pacific and Atlantic ocean cycles, probably linked to solar forcing.
... The discussion of L22 is based on a thorough review of the Medieval Climate Anomaly (MCA; 1000-1200 CE) based on 76 terrestrial and marine sites in South America (Lüning et al., 2019a), including detailed site descriptions and illustrations in a 49 page-long supplementary material. The review concluded that "the vast majority of all South American land sites suggest a warm MCA". ...
... S23 claims that the x-axis is stretched, that the data stop in the middle of the 20th century, and that the original figure of Strelin et al., (2008) might have been "carelessly digitized". Ema Glacier corresponds to site 60 in our South American review (Lüning et al., 2019a). The site description in the Supplement contains several key aspects that S23 appears to have overlooked: ...
... The alleged "distortion" that S23 claims may be related to the recalibration of the radiocarbon ages originally published by Strelin et al. (2008). Details are given in the site description in the Supplement of Lüning et al. (2019a). The data in our figure end at 1950 CE because the original figure of Strelin et al. (2008: their Fig. ...
... The LIA was preceded by the Medieval Climate Anomaly (MCA) which commenced around 800 CE, with a core period at 1000-1200 CE (Lüning et al., 2019a). In a recent literature synthesis (Lüning et al., 2019a) we have demonstrated that Andean glaciers retreated significantly during the Medieval Climate Anomaly (MCA, 1000-1200 CE) when the vast majority of all South American land sites and many other areas worldwide (Lüning et al., , 2019b(Lüning et al., , 2019c, 2020) experienced a natural warm phase. ...
... The LIA was preceded by the Medieval Climate Anomaly (MCA) which commenced around 800 CE, with a core period at 1000-1200 CE (Lüning et al., 2019a). In a recent literature synthesis (Lüning et al., 2019a) we have demonstrated that Andean glaciers retreated significantly during the Medieval Climate Anomaly (MCA, 1000-1200 CE) when the vast majority of all South American land sites and many other areas worldwide (Lüning et al., , 2019b(Lüning et al., , 2019c, 2020) experienced a natural warm phase. This is particularly true for the central Peruvian Cordillera Blanca. ...
... This is particularly true for the central Peruvian Cordillera Blanca. Here, Stansell et al. (2013) studied in sediment cores the geochemical elemental composition of three high altitude lakes that reflect changes in the extent of climate-mediated up-valley ice cover, namely Laguna Queshquecocha (site 20, Fig. 1), Laguna Jahuacocha (site 21), and Laguna Lutacocha (site 22) (all site numbers as listed in our synthesis in Lüning et al., 2019a). The MCA was characterized by generally low clastic input which is interpreted as a glacier retreat phase with lower amounts of erosional detritus. ...
Andean glaciers have been shrinking due to long-term climatic warming during the past 100 years. Stuart-Smith et al. (2021) used observations and numerical models to evaluate the anthropogenic contribution to the centennial retreat of the Palcaraju Glacier in the Peruvian Cordillera Blanca. According to their central estimate, the glacier retreat is thought to be entirely the result of the observed 1 ◦C warming since 1880 in this region, of
which they consider 85–105% as human-induced warming. However, this attribution must be questioned because the numerical models used by the authors fail to replicate the well-documented Andean temperature and glacier history of the Common Era. In a recent literature synthesis we have demonstrated that Andean glaciers retreated significantly during the Medieval Climate Anomaly (MCA, 1000–1200 CE) when the vast majority of all
South American land sites experienced a warm phase, recorded as a near-global natural event, that is not linked with human activity (Lüning et al., 2019a). The MCA was followed by the Little Ice Age (LIA, 1300–1850 CE) when many Andean glaciers advanced significantly, some of them even reaching their maximum Holocene downvalley
extension. In contrast, the “hindcast” of Stuart-Smith et al. (2021) erroneously suggests hardly any glacier length fluctuations for pre-industrial times. Given the unsuccessful “hindcast”, we do not consider the attribution results of the study as robust.
... The comprehensive study of climatic change during the last millennium is of considerable interest as it documents changes from pre-to post-industrial warming or the current warm period (CWP) and documents quantitative changes in the interactions between oceans, atmosphere and biosphere over the last decades within the general longer-term context of climate variability (Lüning et al., 2017;. The MCA warming in South America and the Northern Hemisphere appears to have been largely synchronous, and probably reached comparable intensities (Lüning et al., 2019a). Similar global records of MCA warming were synthesized from different regions of Africa, Antarctica, Mediterranean region, Australia, New Zealand and West Papua (Lüning et al., 2018;2019a;2019b;Lüning et al., 2020). ...
... The MCA warming in South America and the Northern Hemisphere appears to have been largely synchronous, and probably reached comparable intensities (Lüning et al., 2019a). Similar global records of MCA warming were synthesized from different regions of Africa, Antarctica, Mediterranean region, Australia, New Zealand and West Papua (Lüning et al., 2018;2019a;2019b;Lüning et al., 2020). The Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to changes in solar activity by nonlinear dynamics are the chief drivers of the climate variability during the past few millennia (Lüning et al., 2019a). ...
... Similar global records of MCA warming were synthesized from different regions of Africa, Antarctica, Mediterranean region, Australia, New Zealand and West Papua (Lüning et al., 2018;2019a;2019b;Lüning et al., 2020). The Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to changes in solar activity by nonlinear dynamics are the chief drivers of the climate variability during the past few millennia (Lüning et al., 2019a). The global records on the MCA warming have now attained a position which allows compiling palaeoclimate maps for well-defined time intervals. ...
The pollen and diatom analyses of soil samples from a 80-cm deep sedimentary core from the Barak valley of Assam provides an explicit understanding of vegetation, climatic and ecological change in the Indo-Burma region from 580 CE (1370 cal. years BP) to 1220 CE (730 cal. years BP). The impact of the Medieval Warm Period (MWP) has been well documented from palynological records. Based on changes in vegetation succession, the Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) during four pollen phases CP (1-4) were calculated using the coexistence approach. Between 580 and 760 CE (pre-MWP), the occurrence of major riparian tree pollen taxa like Barringtonia, Duabanga and Sapotaceae along with scanty diatom occurrence indicates a warm and relatively less humid climate attributable to a weak Southwest monsoon with low season-ality. This changed to a strikingly enhanced seasonality from 760 to 940 CE (beginning of MWP), indicating the establishment of the dense forest around the lake under increased warm and humid climatic conditions. During the interval from 940 to 1220 CE (MWP peak), the average values of maximum MAT and MAP were the highest recorded (≈31 • C and ≈2250 mm, respectively). From 1220 CE onwards (post MWP), the decline in arboreal pollen coincides with an exponential rise in cereal pollen clumps and shrubby pollen like Melastoma, Cleroden-drum and Justicia adhatoda along with the presence of anthropogenic indicator diatom taxa like Ulnaria ulna and Gomphonema indicating increased landscape changes due to human impact under a relatively less warm and humid climate. In many parts of the world, regional data coverage pertinent to the MCA warming has now reached a point which allows compiling palaeoclimate maps for well-defined time intervals. In this direction, future studies need to address the major climatic data gaps from the Indian sub-continent especially during the last millennia.
... While the first three quarters of the 20th century were affected by prolonged droughts, the western portion of SESA experienced after the early 1970s an unprecedented humid phase characterized by high precipitation and increased river discharges (García and Vargas, 1998;Troin et al., 2016). Over long time scales, variation in the intensity of the SAMS has been identified during key intervals, such as the Last Glacial Maximum, middle Holocene and the last two thousand years (i.e., Chiessi et al., 2009;Cook and Vizy, 2006;Cruz et al., 2009;Kanner et al., 2013;Lüning et al., 2019;Neukom et al., 2010;Neukom and Gergis, 2012;Neukom et al., 2014;Novello et al., 2016;Piovano et al., 2009;Vuille et al., 2012). ...
... 1300 cal yr BP (Fig. 6A). According to the chronology, this episode was contemporaneous with the Medieval Climatic Anomaly (MCA; 800e1400 cal yr BP; Villalba, 1994;Lüning, 2019) which was characterized as a warm and humid period interrupted by cold/dry conditions in the Pampean Plains (Cioccale, 1999;C ordoba et al., 2014;Cuña-Rodríguez et al., 2018;García-Rodríguez et al., 2009;Guerra et al., 2015;Lüning et al., 2019;Piovano et al., 2009;Stutz et al., 2012;Tonello and Prieto, 2010). In the Central Pampas, a humid phase was identified by 746 ± 45 cal yr BP (Guerra et al., 2015), while in the Southeastern Pampas by 1000 cal yr BP (Stutz et al., 2012). ...
... 1300 cal yr BP (Fig. 6A). According to the chronology, this episode was contemporaneous with the Medieval Climatic Anomaly (MCA; 800e1400 cal yr BP; Villalba, 1994;Lüning, 2019) which was characterized as a warm and humid period interrupted by cold/dry conditions in the Pampean Plains (Cioccale, 1999;C ordoba et al., 2014;Cuña-Rodríguez et al., 2018;García-Rodríguez et al., 2009;Guerra et al., 2015;Lüning et al., 2019;Piovano et al., 2009;Stutz et al., 2012;Tonello and Prieto, 2010). In the Central Pampas, a humid phase was identified by 746 ± 45 cal yr BP (Guerra et al., 2015), while in the Southeastern Pampas by 1000 cal yr BP (Stutz et al., 2012). ...
Laguna Mar Chiquita (LMC, 30 54 0 S e 62 51 0 W) is a highly variable and shallow saline lake, located in the Pampean Plains of Argentina. The paleolimnological record of LMC contains information on the environmental variability that occurred in a large area of Southern South America since the Last Glacial Maximum (LGM) until the present. As inferred from the diatom assemblages, sedimentary features and geochemical proxies, prolonged intervals of high and lowstands have caused variations in water salinity, trophic state and sedimentary processes. This is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25,000 cal yr BP in the Argentinean Pampean region. Results are in accordance with well-known global climatic phases. The Late Pleistocene record is characterized by a scenario dominated by lowstands, hypersaline, and oligotrophic lake conditions. Radio-carbon ages (25,000e19,000 cal yr BP) indicate that the onset of the record is coeval with the LGM. Later, a progressive lake water level increase was registered at 17,000 cal yr BP, which can be assigned to the Heinrich Stadial 1. A shift toward comparatively drier conditions identified in the record between 14,700 and 13,000 cal yr BP can be chronologically related to the Antarctic Cold Reversal. The transition from the Late Pleistocene to the Holocene (13,500e10,500 cal yr BP) is recorded by highstand phases while the Early Holocene record is characterized by high to intermediate water levels. The hydrological reconstruction corresponding to the Mid-Holocene is characterized by alternating phases of high/lowstands. The onset of the Late Holocene record is marked by the development of dry conditions and thus lowstand phases, while around 1300 cal yr BP a distinct water lake level increase is recognized. This humid phase, ascribed to the Medieval Climatic Anomaly, is followed by the record of lowstands between 500 and 1000 cal yr BP, being coeval with the Little Ice Age. The uppermost part of the record of LMC encompasses the Current Warm Period, showing a marked shift towards high lake water level conditions. The hydrological variability registered in the paleolimnological record, highlights the importance of Laguna Mar Chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of South Eastern South America.
... The existing ocean current is the Brazil current. Moreover, in Summer other two phenomena affect the climate and precipitation in the north of Santa Catarina, being the South American Monsoon System (SAMS) and the South Atlantic Convergence Zone (SACZ) (James, 1939;Marengo et al., 2012;Novello et al., 2017;Lüning et al., 2019). According to the distribution of the mountain-chains and highlands, in the state there are two groups of mountains, which are, Serra do Mar in the north and the Serra Geral that passes through the middle of the state and makes the highlands of Santa Catarina (Fig. 1). ...
... The two main source of humidity in the coast of Santa Catarina are the Atlantic tropical air mass and the Brazil current. Both characterized to be hot and humid, they flow southward along the coast of the state of Santa Catarina with high concentration of humidity, highlighting the region with high precipitation index (Lüning et al., 2019). Although observed only in Summer, the SAMS and the SACZ have a small weight in annual rainfall regime, mainly in the north of Santa Catarina, where this two factors are more visible (Novello et al., 2017). ...
... As observed in the P a , the precipitation in the coast for the P s in the summer season ( Fig. 5 (a)) is explained by the aggregated action of the Atlantic tropical mass, Brazil current, SAMS, and SACZ (Lüning et al., 2019). Being an orographic factor, the Serra Geral and Serra do Mar complete the accountable features for rainfall occurrence. ...
The average precipitation spatialization in annual and seasonal scale provides important information for the management and maintenance of water resources. Located at the south region of Brazil the state of Santa Catarina has water as its main assets for agriculture and economic development. Therefore, the aim of this study was to spatialize the average annual and seasonal precipitation for the state of Santa Catarina, by means of a geostatistic approach based on models. Data from meteorological stations made available by the Mineral Resources Research Company (CPRM) were used. These stations have regular distribution and high density within the state. For the geostatistical modeling, some basic assumptions such as data normality and nonstationarity were verified. After accepting the assumptions it was verified through statistical tests regarding its likelihood, if the structure of spatial dependence of the geostatistical model increase its performance, justifying the use of this structure for the precipitation spatialization. To check the assumptions of good prediction, the residue dispersion of the spatial interpolations was evaluated through cross-validation. The results showed a better performance for the geostatiscal models with the spatial dependence structure, both for average annual and seasonal precipitation. Thus, these models were used to the spatial interpolation, observing a good prediction through the residual dispersion and, consequently, mapping of precipitation.
... These areas are key to revealing the dynamics and biogeography of different mangrove species. Furthermore, climate anomalies during the last millennium, such as the Medieval Climate Anomaly (MCA, a warmer period during from 1000 to 750 cal yr BP) (Strelin et al., 2008;Neukom et al., 2011) and the Current Warm Period (CWP, since the early 20th century) (Vuille et al., 2012;Lüning et al., 2019) have been documented in studies across South America from the Andrea glaciers to south Brazil, but few studies have revealed the associated ecological responses, especially from the mangrove sub-range limits. Hence, due to these gaps in the literature, it is still unclear whether the poleward mangrove migration toward Santa Catarina was corresponding to the late Holocene climate variability or solely caused by the Anthropocene climate change. ...
... Bay (Fig. 7b), followed by the establishment of Laguncularia and Avicennia in south Santa Catarina from the 1950s (~0 cal yr BP) (Fig. 7a), marking the formation of the modern mangrove belt along the southeastern Brazilian coast (Lacerda et al., 2002). Furthermore, both events coincided with the Current Warm Period (CWP, since the early 20th century) (Vuille et al., 2012;Lüning et al., 2019), especially in SF. Bay, where Rhizophora pollen synchronized with the CWP. ...
The projected warming trend in the 21st century is likely to alter the global distribution of mangroves. However, the migratory pattern of different mangrove species is still unclear, especially in the subtropical Brazilian littoral. This study utilizes pollen, diatom, and organic geochemistry to document the late Holocene morphological and ecological transformation in São Francisco do Sul Bay, the mangrove sub-range limit in south Brazil. This multi-proxy dataset indicates the establishment of saltmarshes and mangroves on muddy tidal flats at~1720 and~870 cal yr BP, and Laguncularia, Avicennia, and Rhizophora colonized the study area at~870,~390, and~70 cal yr BP, respectively. This stepwise succession of three mangrove species in São Francisco do Sul Bay, and poleward mangrove expansion toward the austral mangrove range limit, indicate that the migratory histories of different mangrove species were not synchronized during the late Holocene, and temperature is the primary climatic factor regulating the mangrove distribution in south Brazil. More importantly, the Medieval Climate Anomaly and the Current Warm Period were clearly registered in the pollen record, suggesting that the two climate anomalies likely facilitated the mangroves colonization into higher latitudes in south Brazil. Overall, our dataset indicates that mangrove expansion into more temperate zones will likely accelerate in South America.
... atmospheric effect produced by volcanism, compared to the Northern Hemisphere, probably due to the more accentuated insularity of the southern hemisphere landmasses (Coronato and Bisigato, 1998;Paruelo et al., 1998). By considering a core period around 1000-1200 CE, warmer anomalies were recently identified in South America by Lüning et al. (2019). In contrast with previous syntheses, they observe a synchronicity between the MCA in the Southern and Northern hemispheres, hence supporting the key role of the ocean-atmospheric system (i.e. ...
... These issues could also explain other paleoenvironmental studies which do not even observe a "climatic anomaly" around the MCA time window in Patagonia, which are therefore not treated here (e.g. Bianchi and Ariztegui, 2012;Fesq-Martin et al., 2004;Lüning et al., 2019;Markgraf and Huber, 2010;Markgraf et al., 2003;Musotto et al., 2016Musotto et al., , 2017Pesce and Moreno, 2014;Whitlock et al., 2006; and references therein). ...
This paper revises paleoenvironmental data from Patagonia (southern South America) to discuss the occurrence, characteristics, and human impact of the Medieval Climatic Anomaly (MCA). The analysis of continuous paleoenvironmental archives with multidecadal-to-centennial resolution is based on a quality assessment regarding data interpretation, chronological control, and time range adequacy within the MCA lapse. After applying this threestepped quality filters on the total dataset (N = 48), 18 cases can accurately be ascribed to the MCA. Except for two sites indicating wetter conditions,
these records show dry and/or warm conditions between ca. 750 and 1350 CE (core period at ca. 800–1200 CE). Even though MCA records come mostly from forests and forest-steppe ecotones, all previous archeological hypotheses about the MCA effects on past hunter-gatherers were proposed for the steppes, particularly in southern sectors, thus requiring an assessment of the source of the signal, their synchronicity and causality between human-environmental processes. In the southern steppe, paleoenvironmental records partially overlapping with the MCA time window actually show a predominance of wet conditions between 47° and 50° S, whereas a generalized aridity is recorded in southern tip of the continental Patagonia between 51° and 52° S. Thus, a complex scenario of landscape fragmentation can be supported in the southern steppes during the MCA, produced not only by enhanced aridity in dry environments, but also because of the presence of wet and more resilient areas. This landscape heterogeneity must be considered to deepen the understanding of behavioral changes contemporaneous to the MCA. However, a scenario of demographic growth suggested around 1000 CE for the entire Patagonia could have promoted human changes similar to those expected for the MCA. Finally, no-archeological discussions linked to the MCA were developed for forest regions, despite their robust paleoenvironmental records, implying that changes in proxy data might not have necessarily involved important environmental changes.
... This is important to avoid regional bias in larger-scale T2k composites. For example, the original idea that the MWP may have been predominantly a "regional North Atlantic phenomenon" [17] can no longer be supported because warming associated with the MWP has, meanwhile, also been documented from many other regions of the world, e.g., China, South America, Africa, Oceania and Antarctica [18][19][20][21][22]. ...
... Their T2k composite differs greatly from the studies that use bulk tree ring input. In some cases, composites have erroneously included proxies that later turned out to reflect hydroclimate rather than temperature (examples discussed in 18,19). ...
Global mean annual temperature has increased by more than 1 °C during the past 150 years, as documented by thermometer measurements. Such observational data are, unfortunately, not available for the pre-industrial period of the Common Era (CE), for which the climate development is reconstructed using various types of palaeoclimatological proxies. In this analysis, we compared seven prominent hemispheric and global temperature reconstructions for the past 2000 years (T2k) which differed from each other in some segments by more than 0.5 °C. Whilst some T2k show negligible pre-industrial climate variability (“hockey sticks”), others suggest significant temperature fluctuations. We discuss possible sources of error and highlight three criteria that need to be considered to increase the quality and stability of future T2k reconstructions. Temperature proxy series are to be thoroughly validated with regards to (1) reproducibility, (2) seasonal stability, and (3) areal representativeness. The T2k represents key calibration data for climate models. The models need to first reproduce the reconstructed pre-industrial climate history before being validated and cleared for climate projections of the future. Precise attribution of modern warming to anthropogenic and natural causes will not be possible until T2k composites stabilize and are truly representative for a well-defined region and season. The discrepancies between the different T2k reconstructions directly translate into a major challenge with regards to the political interpretation of the climate change risk profile. As a rule of thumb, the larger/smaller the pre-industrial temperature changes, the higher/lower the natural contribution to the current warm period (CWP) will likely be, thus, reducing/increasing the CO2 climate sensitivity and the expected warming until 2100.
... In tropical mountain ecosystems, abundant literature revolving around the "ecological resilience" concept have associated the lack of human activities as the main factor for ecosystems to remain stable, even with documented climatic changes such as the Medieval Climate Anomaly (900-1100 cal years BP) or the Little Ice Age (270-670 cal years BP) (Lüning et al., 2019). This notion has been supported by study cases documenting forest and aquatic structure recovery after the cessation of deforestation (Norden et al., 2009). ...
... Shifts in benthic vs planktic diatoms have been widely attributed to lake level changes resulting from precipitation variability under warm/dry climates (Weide et al., 2017). For instance, the Medieval Climate Anomaly (MCA) triggered lower lake levels and was recorded on many different tropical Andean paleolimnological records (Lüning et al., 2019). Although the signal of MCA on Lake Llaviucu's sediments is inconclusive (Benito et al., 2021), one consequence of potential warming/drying is an enhanced lake productivity promoted by less mixing within the water column, as seen in analogous moist forest Andean lakes (Loughlin et al., 2018). ...
Anthropogenic climate change and landscape alteration are two of the most important threats to the terrestrial and aquatic ecosystems of the tropical Americas, thus jeopardizing water and soil resources for millions of people in the Andean nations. Understanding how aquatic ecosystems will respond to anthropogenic stressors and accelerated warming requires shifting from short-term and static to long-term, dynamic characterizations of human-terrestrial-aquatic relationships. Here we use sediment records from Lake Llaviucu, a tropical mountain Andean lake long accessed by Indigenous and post-European societies, and hypothesize that under natural historical conditions (i.e., low human pressure) vegetation and aquatic ecosystems' responses to change are coupled through indirect climate influences—that is, past climate-driven vegetation changes dictated limnological trajectories. We used a multi-proxy paleoecological approach including drivers of terrestrial vegetation change (pollen), soil erosion (Titanium), human activity (agropastoralism indicators), and aquatic responses (diatoms) to estimate assemblage-wide rates of change and model their synchronous and asynchronous (lagged) relationships using Generalized Additive Models. Assemblage-wide rate of change results showed that between ca. 3000 and 400 cal years BP terrestrial vegetation, agropastoralism and diatoms fluctuated along their mean regimes of rate of change without consistent periods of synchronous rapid change. In contrast, positive lagged relationships (i.e., asynchrony) between climate-driven terrestrial pollen changes and diatom responses (i.e., asynchrony) were in operation until ca. 750 cal years BP. Thereafter, positive lagged relationships between agropastoralism and diatom rates of changes dictated the lake trajectory, reflecting the primary control of human practices over the aquatic ecosystem prior European occupation. We interpret that shifts in Indigenous practices (e.g., valley terracing) curtailed nutrient inputs into the lake decoupling the links between climate-driven vegetation changes and the aquatic community. Our results demonstrate how rates of change of anthropogenic and climatic influences can guide dynamic ecological baselines for managing water ecosystem services in the Andes.
... For that time interval, some authors have suggested El Niño-like SST conditions in the eastern Pacific (Cobb et al., 2003;Goodwin et al., 2014;Mann et al., 2009;Seager et al., 2007;Steiger et al., 2019), whereas others suggest a La Niña-like SST (Correa-Metrio et al., 2016;Moy et al., 2002;Rustic et al., 2015;Sachs et al., 2009;Toth et al., 2015). However, a recent synthesis indicates that more ENSO inferred paleo-records suggest El Niño rather than La Niña conditions during the MCA (Lüning et al., 2019;Pab on-Caicedo et al., 2019). During the MCA the ITZC had a more northerly position (Lüning et al., 2019;Tierney et al., 2010) and had high amplitude fluctuations (Haug et al., 2001); all this could have fortified the CJ once more, (relatively to the previous dry period) bringing back more moisture to the wetland (at 2020 m asl), similar to those from the mid Holocene. ...
... However, a recent synthesis indicates that more ENSO inferred paleo-records suggest El Niño rather than La Niña conditions during the MCA (Lüning et al., 2019;Pab on-Caicedo et al., 2019). During the MCA the ITZC had a more northerly position (Lüning et al., 2019;Tierney et al., 2010) and had high amplitude fluctuations (Haug et al., 2001); all this could have fortified the CJ once more, (relatively to the previous dry period) bringing back more moisture to the wetland (at 2020 m asl), similar to those from the mid Holocene. ...
The Pacific coast of northern South America, from Panama to Ecuador, also known as the Chocó biogeographic region, is one of the wettest and more biodiverse places on Earth. These wet conditions are caused by the presence of a tropical low-level atmospheric current known as the Chocó low level Jet that transports moisture from the Pacific Ocean to the Andes of Colombia and is responsible for a large portion of moisture entering the continent, reaching as far as the Eastern Cordillera. In order to understand better the climate and ecosystem dynamics of such a wet region, we investigated the past hydroclimate and environmental conditions of a yet an unexplored area, the Medellincito wetland at 2020 m above sea level, located on the water divide of the Western Cordillera of Colombia, under the direct influence of the Chocó Jet. Our results indicate that between ∼6680 and 3710 cal yr BP the wetland had permanent waters and was surrounded by forest. This suggests wet conditions with a strong and persistent Chocó Jet. From ∼3710 to ∼1560 cal yr BP, the wetland dried out and open vegetation dominated by grasses replaced the forest. Later on, between ∼1200 and 750 cal yr BP the wetland formed again although with shallow waters, while open vegetation continued to expand. Humid conditions and the forest were re-established after 750 cal yr BP. We hypothesize that dry conditions in an otherwise very wet area were caused by the weakening of the Chocó Jet, possibly associated with ENSO-moderated changes in the temperature of the Pacific Ocean that coincided with changes in the position, relative to today’s, of the Intertropical Convergence Zone. This record highlights that the ecosystems’ dynamics in the Chocó biogeographic region are highly responsive to variations in moisture from the Chocó Jet, which in turn depends on temperatures in the Pacific Ocean. With current global change leading to the warming of the oceans, this highly biodiverse region can potentially be transformed into grass-rich ecosystems as it had occurred in the past.
... During the Holocene, the STSF shifted the latitudinal position as a consequence of changes in the SWW related to the intensification of ENSO during the last 4000 yr, more recently combined with anthropogenic impacts during the last 200 yr (Bender et al., 2013;Sachs et al., 2018). Furthermore, during the Medieval Climatic Anomaly (MCA), the Brazil Current was intensified Lüning et al., 2018), as well as the adjacent upwelling zone (i.e., Cabo Frío; Lüning et al., 2018). Furthermore, the PPW has changed their northward influence leading to changes in the productivity of the SWAO continental shelf, i. e., higher values after 1500 yr BP related to terrigenous input (Mahiques et al., 2009). ...
... During the Holocene, the STSF shifted the latitudinal position as a consequence of changes in the SWW related to the intensification of ENSO during the last 4000 yr, more recently combined with anthropogenic impacts during the last 200 yr (Bender et al., 2013;Sachs et al., 2018). Furthermore, during the Medieval Climatic Anomaly (MCA), the Brazil Current was intensified Lüning et al., 2018), as well as the adjacent upwelling zone (i.e., Cabo Frío; Lüning et al., 2018). Furthermore, the PPW has changed their northward influence leading to changes in the productivity of the SWAO continental shelf, i. e., higher values after 1500 yr BP related to terrigenous input (Mahiques et al., 2009). ...
Large rivers represent transitional environments between the coast and the open ocean which discharge is influenced by both climate and anthropogenic impacts. In general, historical information on river discharges does not extend beyond 100-yr data series. This is the case of the Río de la Plata (RdlP) watershed, which represents a very important geographic region sensitive to El Niño Southern Oscillation (ENSO). Thus, this study analyzes a continuous millennial, high-resolution record of river discharge oscillation cycles into the ocean and associated productivity changes. We used two 10-m-long sediment cores retrieved from the high-resolution RdlP mud depocenter from the inner continental shelf off Uruguay, namely GeoB 13813-4 and GeoB 13817-2. The first sediment core yielded a mean linear sedimentation rate of 9.7 mm yr − 1 , while the second exhibited a lower resolution, with a mean rate of 7.1 mm yr − 1. Differences in the sedimentation rate are attributed to the distance to the continental source. We performed 2-mm-step-size XRF scanning and used the Ti/Al, Fe/K, Fe/Ca and Si/Al element ratios as proxies for terrigenous supply into the Southwestern Atlantic Ocean (SWAO), and Fe/Mn as a proxy of the redox conditions. At the same time, Ba/Al ratios recorded productivity changes. We detected significant cycles of 50, 20, 10, 2-7 yr, and less than 1 yr for most of the element ratios of both cores. We inferred that cyclicity was related to the Climatic Modes of Oscillation (CMO): Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), Southern Annular Mode (SAM) and ENSO. The CMO play a crucial role in modulating the geochemical characteristic of the terrigenous fine sediments, building up the RdlP mud depo-center. The process of millennial intensification of river discharge, and the associated increase in productivity, were both modulated by the ENSO mode of variability, particularly after the onset of the Little Ice Age (LIA) especially after 1500 CE. During the LIA, ENSO displayed mostly decadal cycles, whilst after the end of the LIA and onset of the Current Warm Period (CWP), the cyclicity intensified to half-decade cycles. After 1970s, river discharge attained maximum magnitude and frequency as a sign of combined natural and anthropogenic forcing, but we also inferred a concomitant increase in productivity. Herein, we introduce evidence that global warming is causing an intensification of the inter-annual hydro-climatic variability within SESA and land-use practices (mainly intensification of soya crops and deforestation) are producing significant soil erosion after 1970. This intensification represents an early warning signal to anticipate a further increase in continental input and productivity within SWAO, which holds both regional and global implicances.
... In order to better assess the magnitude of recent Global Warming, the observed climatic change has to be placed in a longer-term palaeotemperature context. Of particular interest is the Medieval Climate Anomaly (MCA), a recognized period of natural preindustrial climate change associated with marked temperature and hydroclimatic variability in many parts of the world (e.g., Graham et al., 2011;Lüning et al., 2017Lüning et al., , 2018Lüning, Gałka, Bamonte, et al., 2019;Mann et al., 2009). The MCA represents the most recent natural warm phase, preceded in the Northern Hemisphere by the Dark Ages Cold Period (~400-800 CE, Helama et al., 2017) and followed by the Little Ice Age (LIA, 1300-1850, e.g., Shindell, 2009). ...
... A total of 79 Mediterranean localities were identified ( Figure 2 and Tables 1 and S1). This Mediterranean review forms part of an attempt to palaeoclimatically map the MCA on a global scale (Lüning et al., 2017(Lüning et al., , 2018Lüning, Gałka, Bamonte, et al., 2019;Lüning, Gałka, García-Rodríguez, et al., 2019). ...
The Medieval Climate Anomaly (MCA) is a pre‐industrial phase of pronounced natural climate variability with a core period from 1000 to 1200 CE. The paper presents a synthesis that integrates palaeotemperature records from the Greater Mediterranean Region encompassing the past 1500 years based on multiproxy data from 79 published land and marine sites. MCA warming dominated the Western Mediterranean (Iberia, NW Africa) as well as the northern land areas of the Central and Eastern Mediterranean region. MCA cooling prevailed in the Canary Current Upwelling System, southern Levant and some sea areas of the Central and Eastern Mediterranean. Previous palaeoreconstructions suggest persistent positive Atlantic Multidecadal Oscillation (AMO+) and North Atlantic Oscillation (NAO+) conditions during the MCA, whilst the LIA was dominated by an AMO‐ and NAO‐ regime. During the past 150 years, AMO+ conditions are typically associated with warming episodes in the Mediterranean area. A similar relationship appears to have also been established during the MCA as the majority of all Mediterranean land sites experienced warm climate conditions. In contrast, the NAO typically leads to a characteristic west‐east temperature dipole pattern in the basin, as documented for the last decades. During NAO+ conditions the Western Mediterranean is generally warm (and dry), whilst large parts of the Central and Eastern Mediterranean are cold. Similar trends seem to have been developed during the MCA when the NAO+ regime led to consistent warming in the Western Mediterranean, whilst a significant number of sites with MCA cooling existed in the Central and Eastern Mediterranean.
... Despite a lack of robust evidence, some have suggested that the Medieval Climate Anomaly (MCA; 950-1250 CE, or 1000 to 700 BP) was a period when the vast majority of terrestrial sites in South America experienced uniformly warmer conditions (Lüning et al., 2019), and that modern glacial retreat partly represents a recovery from an exceptionally cold Little Ice Age (LIA; 1400-1850 CE, or 550 to 100 BP) (Lüning et al., 2022). Further, they argue that the offset of ~0.8 • C between recent and pre-industrial temperature values should be ascribed more to natural causes than what is commonly used by the Intergovernmental Panel on Climate Change (IPCC) and others (Lüning and Vahrenholt, 2017). ...
Disentangling the timing and pattern of past glacier change in the tropics provides important perspectives for the
future health of the Andean cryosphere. Here we review Holocene paleo-glacial records from the northern and
southern tropical Andes to provide context for the loss of glacial ice since the late 20th century. The available
archives indicate that glaciers advanced and retreated multiple times during the Holocene with notable shifts
during the last millennium. However, the available records of glaciation from the northern and southern Andes
depict contrasting climate conditions across the tropics through the early, middle and late Holocene, including
during the Medieval Climate Anomaly (MCA). There is clearer evidence of widespread Little Ice Age (LIA) glacier
advances throughout the region, however, there were significant, centennial-scale lags in the timing of southern
tropical glaciation relative to the onset of cooling in the Northern Hemisphere. Notwithstanding age uncertainty,
the combined regional paleoclimate records suggest the MCA in the tropical Andes was somewhat warmer and
drier than the LIA, but not warmer than today. In contrast, the vast majority of Andean glaciers appear to be
rapidly and uniformly retreating since the late 20th century in response to anthropogenic warming.
... Such a record can be attributed to the nutrient depletion that occurs after Chaetoceros blooms, indicating high local productivity events (Abrantes et al., 2011;Romero et al., 2015), but also regional high productivity changes related to strong lateral transport from the adjacent Brazilian continental shelf through strengthened influence of the Subtropical Shelf Water (Romero and Armand, 2010;Hatin et al., 2017). As discussed by Perez et al. (2021b), this period was related to the lowest values of marine productivity, hence we suggest that the high record of Chaetoceros appears to be a consequence of regional high productivity, due to the strengthening of the Brazil Current (Chiessi et al., 2014), as well as the adjacent upwelling zone (i.e., Cabo Frío, Lüning et al., 2018), during the Medieval Climate Anomaly (900-1300 CE). ...
Recent studies established a strong connection between instrumental hydroclimatic changes in the Río de la Plata (RdlP) watershed and the influx of continental terrigenous material and productivity changes. This correspondence was further validated for the last millennium. Here, we identified centennial, multi-decadal, and interannual changes in diatom composition, as a proxy for La Plata Plume Water (PPW) discharge into the inner shelf. Core GeoB13813-4 diatom data were revisited, and grouped into freshwater, marine, and brackish categories for multivariate, timeseries, and correlation analyses. Such record exhibits a noteworthy resemblance to paleoclimatic and paleoceanographic variations throughout the past millennium. A Detrended Correspondence Analysis (DCA) on the dominant taxa, and Axis-1 revealed a salinity gradient over the past millennium. DCA1-scores exhibited significant correlation with reconstructions of El Ni˜no Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO) over the same period. By plotting DCA1-scores, we inferred time intervals with varying levels of PPW influence. During ~936–1500 CE, the PPW influence was weak, as the record was dominated by marine taxa, indicating lateral transport from the Brazilian upwelled water and a stronger influence of the Subtropical Shelf Water. After 1500 CE, a well-developed plume was inferred, with the highest influence occurring after 1800 CE, as evidenced by an increased presence of freshwater/brackish taxa. This increased PPW influence after 1500 CE can be attributed to the onset of more humid conditions and associated increased river discharge, particularly under El Ni˜no conditions, with further ENSO intensification after 1800 CE. We identified significant centennial (250 years) and multidecadal cycles (25–50 years) in diatom community composition. These cycles are related to solar forcing, PDO, and AMO. During the 20th Century, cycles of 2 to 7 years were associated with interannual ENSO variability, while 40-year cycles were linked to AMO and PDO variability.
... Period 800 -1200 AD Around 1000-1200 AD, a more intense OMZ was observed, corresponding to the MCA peak that fell during a mostly weaker negative PDO amplitude developed during an extended period (993-1300;MacDonald and Case, 2005). The effects of these environmental conditions in South America have been described based on marine and continental records (Lüning et al., 2019). Marine proxies suggest an intensification of upwelling off Peru and northern Chile concomitant with an intensification of denitrification during this warm period (Salvatteci et al., 2016;Castillo et al., 2017), but others suggest a higher frequency of El Niño episodes in agreement with warmer climatic conditions (Moy et al., 2009, Conroy et al., 2008. ...
The oxygen minimum zone (OMZ) is an essential feature along the Pacific margin, extensively studied for its influence on benthic fauna, acquiring relevance in coastal zones due to its impact on aquaculture species, marine-managed areas, and marine-protected areas. The most evident temporal variability beyond seasonal timescales observed for the OMZ was related to inter-annual variability associated with El Niño, when warmer and more oxygenated waters arrive at shallower zones and the OMZ becomes deeper. However, the impact of oxygen-deficient water that appears sporadically over the shelf is not yet understood. This study provides an integrated view of the oceanographic and climatic conditions behind bottom oxygen conditions along the Chilean continental margin, considering the temporal variability in the South East (SE) Pacific during the last~2000 years. We organized the information on redox-sensitive metals and d 15 N from sedimentary cores obtained from shelf zones from 23°S to 36°S at water depths lower than 100 m. The results demonstrate the variability in the upper part of the OMZ over the shelf, which seems to respond to climatic oscillations. The element distribution indicated in particular a more intense OMZ was developed over the shelf before 1400 AD, followed by more oxygenated bottom conditions afterward, except between 1925 and 1970 off 36°S when the OMZ was intensified, a condition that was not observed at the northern sites. This period mostly coincided with a low Pacific Decadal Oscillation amplitude and reduced El Niño Southern Oscillation (ENSO) Frontiers in Marine Science CITATION Muñoz P, Castillo A, Valdé s J and Dewitte B (2023) Oxidative conditions along the continental shelf of the Southeast Pacific during the last two millennia: a multiproxy interpretation of the oxygen minimum zone variability from sedimentary records.
... Interestingly, this sociopolitical unravelling occurred slightly after the onset of the Medieval Climate Anomaly (MCA), a centuries-long global climate perturbation that occurred from ca. 1.05-0.70 ka (AD 950-1300) (Lüning et al., 2019). Previous research demonstrated that the MCA broadly affected human behavior around the world. ...
The archaeology of the pre-contact Andes provides an ideal study of human responses to climate change given the region's extreme climatic variability, excellent archaeological preservation, and robust paleoclimate records. We evaluate the effects of climate change on the frequency of interpersonal violence in the south-central Andes from ca. 1.5–0.5 ka (AD 470–1540) by comparing incidents of skeletal trauma observed among 2753 crania from 58 sites to rates of ice accumulation at the Quelccaya Glacier. We find that, in the highlands, the odds of identifying inter-personal violence increase on average by a multiplicative factor of 2.4 (1.8–3.2; 95% C.I.) for every 10-centimeter decrease in annual ice accumulation. Our statistical analysis does not detect a relationship between ice accumulation and interpersonal violence rates among coastal or mid-elevation populations. This disparity likely resulted from variable economic and sociopolitical strategies at different elevations. The failure of rain-fed agriculture during periods of drought and concomitant dissolution of organizing polities likely predisposed highland populations to socioeconomic stress and violent competition for limited resources. Conversely, diversity among lowland and midland economies may have buffered against the effect of drought.
... A wet Medieval Climate Anomaly (MCA) between ca. 950 and 750 a cal BP (Lüning et al., 2019), relatively well described only in a few records was followed by drought at the onset of the Little Ice Age (LIA) ca. 650 and 100 a cal BP (Rabatel et al., 2008;Gonz alez-Pinilla et al., 2021). ...
Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 °S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species-specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n-C24 and n-C28) increased with hyperaridity. Similarly, analysis of n-alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distributions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n-alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region.
... Moreover, the apparent fall-off around 1000 cal BP also coincides with irregularities in the calibration curve. We cannot exclude the possibility that the apparent climax after 900 cal BP is a consequence of the joint contribution of lesser degrees of taphonomic loss in more recent stratigraphic layers and rapid variations in atmospheric 14 C related to the Medieval Climate Anomaly (Hughes and Diaz 1994;Lüning et al. 2019). ...
Food production is one of the most significant achievements in Andean history. The domestication of plants and animals presented an enormous challenge, relating to changing technologies, settlement patterns, and social organization. This paper aims to assess Atacama Desert population dynamics and their relationship to the domestication of plants and animals through chronological modeling using kernel density estimation on radiocarbon (14 C) dates, assuming that a higher 14 C probability density is related to more intense human occupation. The analysis is based on a 14 C dataset comprising 1003 14 C dates (between 11,000 and 150 BP) from 243 archaeological sites in the Arica and Tarapacá regions of northern Chile, collected from published data. We observed two population-dynamics inflection points for these regions. First, starting at ca. 3000 BP, constant population growth occurred, which was related to horticulture in the Arica region and to agriculture in the Tarapacá region. Second, between ca. 1000 and 400 BP, a general population rise occurred due to the consolidation of intensive agriculture in the lowlands and precordillera altitudinal belts in both regions and the integration of the coast and the altiplano into macro-regional population dynamics.
... Hubber, 2010; Sottile et al., 2012;Echeverría et al., 2018Echeverría et al., , 2022Vilanova et al., 2019;Marcos et al., 2022a), as well as the climatic patterns and the dynamics of the glaciers (e.g., Glasser et al., 2004Glasser et al., , 2011Villa-Martínez & Moreno, 2007;Moreno et al., 2012;Flantua et al., 2016;Lüning et al., 2018;Horta et al., 2019) were analyzed. ...
Abstract. In this research, we reconstruct the paleoenvironmental conditions from a sedimentary record of a wetland (mallín) located in the Patagonian steppe near to the Subantarctic forest on the northeastern shore of the San Martín Lake basin (SW Santa Cruz, Patagonia, Argentina). The Mallín Ñire (49° 00’ 23.5” S; 72° 13’ 34.5” W) presents a basal age of 10,200 cal. years BP and its pollen content, carbon isotopes, and stratigraphy were analyzed. The relationship with modern pollen assemblages from surface sediment samples allows us to interpret changes in the fossil record. Between 10,200 and 9,000 cal. years BP, we can infer a grass-shrub steppe with dwarf-shrubs under arid conditions and
between 9,000 and 6,500 cal. years BP, a grass steppe dominated under an increase of moisture availability. Conditions became drier until 4,000 cal. years BP; later, a grass-shrub steppe developed, which suggests an environmental transition like the modern ones. The last 1,400 cal. years BP present high paleoenvironmental variability. The integration with other sequences allowed us to interpret the regional changes during the Holocene related to moisture availability by precipitation changes related to the westerly variations.
... Moreover, the apparent fall-off around 1000 BP also coincides with irregularities in the calibration curve. We cannot exclude the possibility that the apparent climax after 900 BP is a consequence of the joint contribution of lesser degrees of taphonomic loss in more recent stratigraphic layers and rapid variations in atmospheric 14 C related to the Medieval Climate Anomaly (Hughes and Diaz 1994;Lüning et al. 2019). ...
Esta tesis busca comprender los cambios en la economía política de las poblaciones del Colesuyu generados por su integración al Tawantinsuyu. Se discuten las estrategias de control incaicas y el uso de las infraestructuras locales al servicio de los intereses del Estado a partir del análisis de la producción y las interacciones. En este contexto, se analiza la gestión del excedente agrícola mediante el estudio de las infraestructuras de almacenamiento, así como los flujos de movimiento de personas productos e ideas mediante el estudio del palimpsesto vial.
Se plantea una aproximación metodológica que combina el modelamiento de datos espaciales y cronológicos con la fotointerpretación de imágenes aéreas, la prospección pedestre intensiva y el análisis arquitectónico, estratigráfico y cronológico aplicados a caminos (trayectorias lineales) y almacenes (arquitecturas fijas).
Durante la segunda mitad del período Intermedio Tardío, a partir del 1300 d.C., el almacenamiento comunitario de maíz se incrementó de forma sostenida a la par del continuo crecimiento de la producción agrícola en los valles de Lluta y Azapa. La organización espacial de los sistemas de almacenamiento sugiere una centralización parcial y una gestión local que fue sostenida por colectivos diferenciados al interior de los asentamientos. Paralelamente, las redes viales articularon al sistema de asentamientos de los Valles Occidentales, identificándose flujos de movimiento regulares tanto transversales (entre pisos ecológicos) como longitudinales (entre cuencas en un mismo piso), reflejando interacciones complejas y multidireccionales a lo largo de ejes viales diversos.
Durante el período Tardío, a consecuencia de la integración del Colesuyu al imperio incaico se incrementó la producción agrícola excedentaria como parte de un proceso de especialización maicera. Asimismo, las infraestructuras de almacenamiento alcanzaron su mayor tamaño y concentración, lo que sugiere una mayor centralización en la gestión del excedente en el seno de las poblaciones asentadas en los valles. Mientras que en la precordillera se instauró infraestructura de almacenaje estatal destinada a capturar parte de la producción local. El control vial se manifiesta a través de la concentración de los flujos en dos ejes viales principales que formaron parte del Qhapaq Ñan, el camino Precordillerano y el camino Lluta, y el establecimiento de arquitecturas y materiales incaicos en ambos ejes.
En síntesis, en esta tesis propongo que la implementación del sistema Inca en el Colesuyu estuvo fuertemente basada en configuraciones locales. La planificación del control estatal favoreció la adaptación y fortalecimiento de las infraestructuras y dinámicas locales preexistentes en paralelo a una baja inversión en infraestructuras incaicas, las que se orientaron a ampliar y controlar la base productiva y la interacción regional mediante la centralización de los flujos de movimientos como del control de la producción excedentaria.
... The Lago Pichilaguna diatom record suggests a warm/dry interval between~1000-900 cal yr BP that overlaps with the chronology of the Medieval Climate Anomaly (MCA) reported by Stine (1994) and Villalba (1994) on tree-ring and radiocarbon-dated Patagonian records. This was followed by a cold/wet phase be-tween~300-200 cal yr BP that overlaps in timing with the culmination of the Little Ice Age (LIA) (Bond et al., 2001;Lüning et al., 2019;Villalba, 1994). Palynological studies conducted in NWP, fail to record this climate shift (Moreno et al., 2018;Moreno, 2020;Jara and Moreno, 2012) and, instead, show a signal dominated by nonclimatic deforestation and proliferation of non-native plant species of European origin. ...
Little is known about the response of terrestrial and aquatic ecosystems to changes in climatic and human influences during the last millennium in northwestern Patagonia (NWP, 40°-44°S). By virtue of their sensitivity and specificity, diatoms are ideal for examining past changes in aquatic ecosystems and deciphering the ranges of variability under natural and human-induced conditions. To date, however, very few fossils diatom studies have examined in detail the environmental evolution during the last millennium throughout Patagonia. Here we present a fine-resolution diatom record from a lake-sediment core collected from Lago Pichilaguna (41°S), a closed-basin and shallow lake with a small catchment area located in the lowlands of the Chilean Lake District in NWP. The record spans the last millennium with a median time resolution of ∼12 years between samples, and shows abundant small Aulacoseira spp. between ∼1000-900 and ∼600-300 cal yr BP, which alternate in dominance with small fragilarioids and small raphid diatoms between ∼900-600 and ∼300-200 cal yr BP. A rapid shift to planktonic diatoms started at ∼200 cal yr BP and led to their modern dominance. We interpret centennial-scale changes in temperature, precipitation, and lake turbulence, with warm/dry/stratified phases between ∼1000-900 and ∼600-300 cal yr BP related to weak westerly winds, and intervals of cold/wet and mixed water column conditions between ∼900-600 and ∼300-200 cal yr BP, favored by stronger winds. The transition from periphytic to planktonic diatoms that started at ∼200 cal yr BP suggests juxtaposition of the warmest/driest phase of the last millennium and the onset of large-scale disturbance by Chilean/European settlers in NWP. Our results reveal that human disturbance during historical time surpassed the natural ranges of variability and resilience of aquatic and terrestrial ecosystems over the last millennium, generating abrupt changes in biodiversity, species composition, and community structure.
... A adoção do último termo tem sido preferencial desde então, visto que ele reflete a disponibilidade de muito mais informações sobre a temperatura e hidrologia antes inexistentes. A ACM representa uma fase de aquecimento natural mais recente na história milenar, fornecendo informações de contexto cruciais para compreender e contextualizar o Período Quente Atual (PQA) e seu processo de aquecimento(DIAZ et al., 2011;LÜNING et al., 2019). ...
Efforts to place recent climate observations in a long-term context have been driven by concerns about whether the global warming trend of the 20th century is part of natural climate variability or whether it is linked to increased anthropogenic emissions of greenhouse gases in the atmosphere. A new perspective on the climate and its changes is offered, highlighting those that occur due to natural cycles, which are generally not widespread. With the historical background on how the climate varied in the past, statistical research was conducted using time series techniques and spectral/harmonic analysis (Fourier series and spectrograms), which allowed the determination of periodic natural phenomena and their magnitudes in national variations of temperature. It was identified that the air surface temperature in Brazil expresses cycles of 4 years (oceanic-atmospheric origin related to ENSO), 33 years (Brückner cycles, lunar-solar origin) and 82 years (lower Gleissberg cycle, solar origin). Based on an alternative oscillatory model that incorporates such natural cycles, future projections of the air temperature in the country were prepared. For the year 2100, it is predicted that the air temperature in Brazil may reach the value of +1.8 ± 0.6 °C, according to the natural oscillatory model. In comparison, conventional models typically used by the IPCC indicate, by the end of the century, an increase of: +2.9 ± 1.2 °C (RCP4.5 model, with mitigation); +3.9 °C (SRES A1 model); and +5.7 ± 1.7 °C (RCP8.5 model, without mitigation). The most extreme values of conventional models reach proportions up to 4 times greater than the results obtained in the alternative model provided here. Analyzing the adherence of the models, it is concluded that the conventional models are overestimating and exaggerating a warming rate in Brazil that, in reality, has not been observed. The proposed natural oscillatory model, which has a high correlation with the data observed so far, indicates an increase in temperature in Brazil that may reach a modest value of +0.8 °C in 2040. For the same year, the SRES A1 and RCP8.5 models indicate values around +2.0 °C – which represents more than double of the projection based on natural climate cycles. Based on the projections that indicate a moderate warming, not so exaggerated, a new perspective of a less terrifying future climate is offered. In a context in which pernicious alarmist discourses predominate, spreading scenarios of apocalyptic global warming, it is hoped that new pondered views could help to appease the level of concern that today, has culminated in undesirable side effects - especially the high levels of eco-anxiety that has afflicted significant portions of society.
... During the following two centuries, between 1000 and 1200 AD, forest cover underwent a new sudden and dramatic decline. This phase coincides with the so-called Medieval Climate Anomaly (MCA), a period of pronounced natural climatic variability marked by significant temperature and hydroclimatic oscillations all around the globe [97][98][99]. Since Lamb [100] first proposed an "Early Medieval Warm Epoch", later changed to "Medieval Warm Period", increasing evidence for this rapid climate change emerged, revealing a complex climatic scenario marked by distinct regional expressions [101]. ...
This study presents the first Late Holocene marine pollen record (core ND2) from SE Sicily. It encompasses the last 3000 years and is one of the most detailed records of the south-central Mediterranean region in terms of time resolution. The combined approach of marine palynology and historical ecology, supported by independent palaeoclimate proxies, provides an integrated regional reconstruction of past vegetational dynamics in relation to rapid climatic fluctuations, historical socio-economic processes, and past land-use practices, offering new insights into the vegetation history of SE Sicily. Short-term variations of sparse tree cover in persistently open landscapes reflect rapid hydroclimatic changes and historical land-use practices. Four main phases of forest reduction are found in relation to the 2.8 ka BP event, including the Late Antique Little Ice Age, the Medieval Climate Anomaly, and the Little Ice Age, respectively. Forest recovery is recorded during the Hellenistic and Roman Republican Periods, the Early Middle Ages, and the last century. Agricultural and silvicultural practices, as well as stock-breeding activities, had a primary role in shaping the current vegetational landscape of SE Sicily.
... Temperature data were not available for the Australian site and were therefore estimated for 1900 using the Willmott and Matsuura dataset35 . The southern Argentinian samples were estimated to be ≈ 860 years old, thus the temperature and precipitation data for the Argentinian site were estimated according to other climate models71,72 . ...
Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO 2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO 2 to O 2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO 2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO 2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO 2 , in particular for mire structures with intermediate water table depths.
... The MCA is a multi-centennial period of anomalous warming between ∼1,000 and 700 cal BP (AD 950-1250), originally identified in northern hemisphere palaeotemperature proxies (Bradley et al., 2003;Mann et al., 2009). Narrowing data gaps across tropical South America have found support for its expression as a period of abrupt hydroclimate change over central and eastern Brazil too, with precipitation proxies suggesting depressed rainfall due to a northward shift of the Intertropical Convergence Zone (ITCZ) and lowered moisture delivery across the continent (Novello et al., 2018;Deininger et al., 2019;Lüning et al., 2019). Following the MCA, the Little Ice Age (LIA) manifests in the northern hemisphere as a period of cooling, which in South America shows a signal that varies from wet to dry, depending on the position within the path of the South American Monsoon System (SAMS). ...
The study of resilience is a common pathway for scientific data to inform policy and practice towards impending climate change. Consequently, understanding the mechanisms and features that contribute towards building resilience is a key goal of much research on coupled socio-environmental systems. In parallel, archaeology has developed the ambition to contribute to this agenda through its unique focus on cultural dynamics that occur over the very long term. This paper argues that archaeological studies of resilience are limited in scope and potential impact by incomplete operational definitions of resilience, itself a multifaceted and contested concept. This lack of interdisciplinary engagement fundamentally limits archaeology’s ability to contribute meaningfully to understanding factors behind the emergence and maintenance of long-term societal resilience, a topic of significant interest that the field is in theory ideally positioned to address. Here, we introduce resilience metrics drawn from ecology and develop case studies to illustrate their potential utility for archaeological studies. We achieve this by extending methods for formally measuring resistance, the capacity of a system to absorb disturbances; and resilience, its capacity to recover from disturbances, with a novel significance test for palaeodemographic data. Building on statistical permutation and post-hoc tests available in the rcarbon package in the R statistical environment, we apply our adapted resilience-resistance framework to summed probability distributions of calibrated radiocarbon dates drawn from the Atlantic Forest of eastern Brazil. We deploy these methods to investigate cross-sectional trends across three recognised biogeographical zones of the Atlantic Forest domain, against the backdrop of prehistoric phases of heightened hydroclimatic variability. Our analysis uncovers novel centennial-scale spatial structure in the resilience of palaeodemographic growth rates. In addition to the case-specific findings, we suggest that adapting formal metrics can help archaeology create impact and engagement beyond relatively narrow disciplinary concerns. To this end, we supply code and data to replicate our palaeodemographic analyses to enable their use and adaptation to other archaeological problems.
... Climate reconstructions from individual proxies also provide useful descriptions of past temperature conditions in the AP and SPat. A group of available reconstructions are summarized in Fig. 9 and Supplementary Material 3. Site descriptions, illustrations and references are detailed in the Supplements of Lüning et al., (2019a) and Lüning et al., (2019b). Proxy information in the AP suggests: MCA warmer than LIA in sites 1, 2, 4, 6 and 9; MCA colder than LIA in site 5; MCA similar to or warmer than PD in sites 1, 3, 7 and 8. Proxy information in SPat suggests: MCA warmer than LIA in sites 10, 11, 13, 14, 15, 16, 17 and 18; MCA warmer than PD in sites 10 and 11; MCA colder than PD in site 12. ...
This paper describes differences between Medieval Climate Anomaly (MCA) and present-day temperatures in the area composed of the Antarctic Peninsula, southern Patagonia, and the surrounding southern oceans. The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME) considering the impact of each natural (volcanic activity and solar variability) and anthropogenic (greenhouse gas, ozone-aerosols and land use/land cover) individual forcing relative to the full forced simulations. Model results show generalized warming during the MCA in the study area. However, the simulated MCA temperatures are significantly colder than present-day mean values due to the influence of increased atmospheric greenhouse gas concentrations since the beginning of the modern Industrial Era in the ∼1850s. In fact, model runs in which only natural forcings were applied show that, in the absence of greenhouse gas forcing, present-day temperatures in the Antarctic Peninsula and southern Patagonia would be lower than or similar to those during the MCA. The study demonstrates the value of paleoclimate proxy–model comparisons but also highlights the limitations of current available proxy information to perform that integration in the study area.
... A good candidate to reveal the ENSO-ASM relationship on the decadal timescale and determine whether it is natural or human forced is the medieval warm period (MWP) (defined by Lamb (1965) as a "warm climate" period between 950 and 750 yr B.P.), when the climate operated naturally. Remarkable progress has been achieved in reconstructing the general trends of global climate change during the MWP (Zhang et al., 2008;Ling et al., 2018;Luning et al., 2019). Specifically, in China, historical documents suggest a warmer MWP than the current warm period (CWP, Zhang, 1993). ...
El Niño/Southern Oscillation (ENSO) is Earth's dominant interannual climate variability mode, but knowledge about its relationship with the Asian summer monsoon (ASM) during the medieval warm period (MWP) is limited, hampering predictions of ASM changes. Here, we present a high-resolution and annually layered stalagmite δ¹⁸O record covering most of the MWP (from 1050 to 665 yr B.P.) from Xiaoshanyan Cave, which is located in the middle reaches of the Yangtze River in Central China. We combined ²³⁰Th dates and annual-layer counting to derive an age model for the δ¹⁸O record (an ASM proxy) and identified a peak-trough-peak structure in the ASM across the MWP, which has also been found in other Chinese proxy records. The weak monsoonal interval (900–750 yr B.P.) corresponds to the Oort minimum period, indicating that the ASM could have been impacted by centennial-scale solar activity through air-sea amplifications. On the multidecadal timescale, a remarkable anti-phased relationship was observed between our record (tuned 7 yr older for synchronization) and the historically documented dry-wet record. This suggests that calcite δ¹⁸O values should reflect the relative contributions of two different water vapour sources from tropical and subtropical oceans rather than the amount of precipitation on short timescales. Comparison of the data further showed that both our δ¹⁸O record and the dry-wet index strongly correlate with the frequency and amplitude of ~30-yr ENSO cycles, indicating that the ASM sensitively responded to ENSO activity during the MWP. We thus confirmed that ENSO modulated the hydroclimate in the monsoonal regions of China during the MWP, which is also the case in the current warm period.
... From then on, the current semi-arid climate would have established itself with humid intervals displaying secular temporal patterns and sudden humid pulses, occurring on a decennial scale, especially in the last 3 ka , connected with events observed both worldwide and in the South American context. In the past 3 ka, the occurrence of the Medieval Climatic Anomaly (MCA) has been responsible for widespread hot and dry conditions in South America Novello et al., 2018;Lüning et al., 2019), due to the further northern positioning of the ITCZ. According to Novello et al. (2012), the same condition occurred at the Diamantina Plateau. ...
River streams are sensitive to environmental changes in drainage basins in response to external and internal forcing. These changes lead to drainage channel adjustments and may alter erosion-sedimentation cycles along valleys, as well as short and long term geomorphological evolution. Concerning the low latitude semi-arid region in South America, fluvial responses to environmental changes during the Upper Holocene have still not been adequately assessed, contrasting with evaluations in river drylands located in middle latitudes. To collaborate with assessments on Upper Holocene climatic fluctuations, alluvial deposits at the Itapicuru River, located in the Brazilian semi-arid, were analyzed to understand this river's dynamics in the last 5 ka and its relationship with both intrinsic and extrinsic factors. The following analyses were performed: [1] spatial terrace distribution throughout the river's longitudinal profile, [2] stratigraphic section assessments, [3] OSL dating, to estimate surface time elaboration, and [4] age correlations with regional paleoclimatic models. In the last 2.2 ka, downcutting and lateral migration occurred at the same time due to fluvial discharge changes over centuries and decades. Semi-arid conditions, such as those currently observed, prevailed throughout the drainage basin, with wet intervals identified upstream. Humidity variations were responsible for middle valley incision and deposi-tion, forming terrace, bars, and natural levees. These findings indicate that, at least in our case study, intrinsic factors had big importance to control the fluvial dynamics since the establishment of the semi-arid low latitude climatic conditions.
... (Mann et al., 2009;Neukom et al., 2014). New evidence, however, indicates that warmer conditions around the MWP occurred in both the tropics and the extratropics of the Southern Hemisphere (e.g., Cook et al., 2002;Meyer and Wagner, 2008;Lüning et al., 2019). Conversely, a high frequency of wet years was recorded between 1550 and 1700 in our SPEI Nov-Dec reconstruction, which broadly coincides with the colder period between the 13th through 19th centuries recognized as the Little Ice Age (LIA). ...
State-of-the-art climate models project droughts of stronger intensity and longer persistence in many arid and semi-arid regions such as northern Patagonia, which constitutes a serious concern worldwide. Moisture availability has a significant influence on the dynamic, stability and function of terrestrial ecosystems. In this study, we used wood samples from 260 Austrocedrus chilensis trees growing in northwestern Patagonia to reconstruct the Standardized Precipitation Evapotranspiration Index (SPEI) for the last millennium (1055–2014). Our reconstruction explained 41.6% of the variance contained in the November–December SPEI at a 1-month scale for the period 1930–2013. The SPEI reconstruction has provided a long record of extreme pluvial (1060s, 1090s, 1200s, 1300s, 1360 s2, 1390s, 1400s, 1550s, 1580s, 1580s, 1630s, 1940s, 1960s, and 2000s) and drought events (1070s, 1150s, 1170s, 1180s, 1270s, 1310s, 1430s, 1450s, 1570s, 1600s, 1620s, and 1950s) for northwest Argentine Patagonia. Although the SPEI reconstruction indicates that the frequency of extreme events has increased since 1950, our record indicates that current levels have not exceeded those previously reached, particularly when compared to those recorded around the suggested periods for the Medieval Warm and towards the end of the Little Ice Age. The spatial and temporal relationships associated with the South Annular Mode and the Pacific Sea Surface Temperature variability as expressed by the Tripole Index indicated that the temporal variability observed in the SPEI reconstruction is modulated by hemispheric-scale atmospheric circulation dynamics. These climate forcings are likely responsible for the intensity and the rate of occurrence of extreme weather events in northwestern Patagonia. Furthermore, the SPEI reconstruction showed a spatial and temporal pattern similar to that observed in previous PDSI-based reconstructions. This study provides robust evidence of hydroclimatic variations for extratropical sectors of South America, improving our knowledge of the climate dynamics during the last millennium and allowing us to review the recently observed increase in wet and dry events in a long-term historical context.
... For instance, changes in Lake Yahuarcocha's diatom record closely matched dry-wet climatic fluctuations associated with the Medieval Climate Anomaly and Little Ice Age. This link was indicated by elastic changes of tychoplanktic (Aulacoseira spp) and halophilous (Craticula halophila, Epithemia) diatoms, coupled with evidence for precipitation-evaporation changes (δ 18 O and CaCO 3 ) (Fig. S7) (Lüning et al. 2019). Other paleolimnological studies have recorded climate-driven lake level fluctuations in the tropical Andes, inferred by gradual biological responses (diatom and pollen). ...
Little is known about whether changes in lake ecosystem structure over the past 150 years are unprecedented when considering longer timescales. Similarly, research linking environmental stressors to lake ecological resilience has traditionally focused on a few sentinel sites, hindering the study of spatially synchronous changes across large areas. Here, we studied signatures of paleolimnological resilience by tracking change in diatom community composition over the last 2000 years in four Ecuadorian Andean lakes with contrasting ecoregions. We focused on climate and anthropogenic change, and the type of biological responses that these changes induced: gradual, elastic, or threshold. We combined multivariate ordination techniques with nonlinear time‐series methods (hierarchical generalized additive models) to characterize trajectories of community responses in each lake, and coherence in such trajectories across lakes. We hypothesized that remote, high‐elevation lakes would exhibit synchronous trends due to their shared climatic constraints, whereas lower elevation lakes would show less synchronous trends as a consequence of human density and land‐cover alteration. We found that gradual and elastic responses dominated. Threshold‐type responses, or regime shifts, were only detected in the less remote lake, after a long period of gradual and elastic changes. Unexpected synchrony was observed in diatom assemblages from geographically distant and human‐impacted lakes, whereas lakes under similar broad‐scale environmental factors (climate and ecoregion) showed asynchronous community trajectories over time. Our results reveal a complex ecological history and indicate that Andean lakes in Ecuador can gradually adapt and recover from a myriad of disturbances, exhibiting resilience over century to millennial timescales.
... and~0.4 cal ka BP in the Lago Fonk record that overlaps in timing with the Little Ice Age (Lüning et al., 2019;Villalba, 1994). The onset of large-scale disturbance by settlers was coincident with a widespread and severe drought in 1863 CE that affected the Longitudinal Valley as far south as 40 S, according to a recent tree-ring based drought-severity reconstruction (Morales et al., 2020). ...
Climate and disturbance regimes play key roles in shaping the structure, composition and functioning of terrestrial ecosystems. Despite this importance, very few stratigraphic studies in the temperate rainforests from northwestern Patagonia have explored this relationship in detail along a time continuum through the entire Holocene. Here we present a high-resolution fossil pollen and charcoal record from Lago Fonk (median resolution: 20 years), a small closed-basin lake in the lowlands of the Chilean Lake District (41°S), where wildfires and explosive volcanism have intermittently taken place during the Holocene, along with pronounced human-induced disturbance in post-colonial time. Our results show persistence of temperate rainforest throughout the Holocene, with changes in the composition and structure of Valdivian rainforests (VRF) at millennial timescales. We detect centennial-scale alternations in dominance between the VRF tree Eucryphia/Caldcluvia and generalist trees found in VRF and North Patagonian rainforests after ∼6.5 cal ka BP. Intervals dominated by VRF coincide with enhanced fire occurrence signaling negative hydroclimate anomalies with a mean duration of ∼150 years, which alternate with positive hydroclimate anomalies lasting ∼312 years on average.
Our results suggest that the magnitude and rapidity of vegetation changes detected at 10.2–9.9, 4.0–3.0, ∼1.0, and ∼0.7 cal ka BP were amplified by disturbance regimes, and led to the establishment and maintenance of Eucryphia/Caldcluvia-dominated forests in the Longitudinal Valley of the Chilean Lake District. On several occasions the higher incidence of fire disturbance during warm/dry climate intervals coincided with episodes of heightened explosive volcanic activity from multiple eruptive centers within the Southern Andean Volcanic Zone.
... As a result of these different modes of climatic variability, the Pampean lakes have shown important lakes level changes during the Holocene, as demonstrated in Laguna Mar Chiquita (Cuña-Rodriguez, 2018;Coianiz et al., 2014;Piovano et al., 2014;2004;2002), Lagunas Encadenadas del Oeste de Buenos Aires (Córdoba, 2012, Lake Nahuel Rucá (Stutz et al., 2010), Lake Lonkoy (Stutz et al., 2012), Lake La Barrancosa (Plastani et al., 2019), Lake Adela (Dangavs and Mormeneo, 2012), Laguna del Monte (Dangavs and Pierrard, 2013), Lake La Brava (Irurzun et al., 2014;Laprida et al., 2014) and Lake Melincué (Guerra et al., 2015(Guerra et al., , 2017 (Fig. 1). Despite the existence of some paleohydrological reconstructions, multiproxy inferences in the southern Pampas (classification according to Iriondo, 1994) are still needed to provide additional information on the timing and relationship of local hydrovariability with large-scale climatic events (Guerra et al., 2017;Lüning et al., 2019). Moreover, understanding the interaction of past climatic changes with limnological features is also crucial to face future challenges such as the synergic effect of climate warming and eutrophication on local/endemic biodiversity (Kopprio et al., 2010). ...
The Pampean region is a crucial area to obtain sensitive paleoclimatic lacustrine archives due to the presence of
shallow environments in a territory non impacted by humans until the last centuries. In this study, we provide a
paleoecological reconstruction for the last ca. 700 years based on a multiproxy lacustrine record from Laguna
Blanca Grande, in Olavarría (Buenos Aires, Argentina). Our inferences, which were based on sedimentary
properties, diatom, cladoceran and ostracod assemblages, offered interesting information about hydroclimatic
variability and nutrient increase. Changes in relative abundances on diatoms, specifically on Aulacoseira granulata and Aulacoseira granulata var. angustissima and fragilariods, were used to infer shifts in nutrient conditions.
The remainder proxies together indicated small lake level changes. Reconstructed hydroclimatic conditions in
Laguna Blanca Grande are consistent with previous paleoecological inferences indicating a humid phase around
ca. AD 1450 and progressive drier conditions ca. AD 1530–1900. A flood gate construction and an increase of
nutrients in the lake revealed a higher human pressure due to population increase and land-use changes during
the last century. Further studies on taxonomy and autecology of microcrustaceans are needed to effectively
unlock the information contained in biological proxies from Sudamerican records
... The Medieval Climate Anomaly (MCA, AD 800-1300), one of the most recent naturally warm period for most areas of the world (Soon et al., 2003;Loehle and McCulloch, 2008;Lüning et al., 2017Lüning et al., , 2019, can be used to test the natural climatic variations with changes induced by more recent human activity. Therefore, high resolution proxy climate archives during MCA will be very helpful for understanding the interaction between different regional climate systems in order to provide some historical context and perspective for the expected anthropogenic global warming. ...
The nature of how the El Niño–Southern Oscillation (ENSO) and its seasonality respond to warmer climate is critical knowledge to predict future climates under the expected anthropogenic warming scenario. In this study, a sub-fossil Tridacna gigas specimen was collected from the northern SCS and AMS¹⁴C dating suggested that the animal lived around AD 1099, during the Medieval Climate Anomaly (MCA) interval, the most recent natural warm period of the late Holocene. Monthly Sr/Ca ratios were determined by the ICP-OES measurements and a 30-year long SST record was calculated based on a Sr/Ca-SST calibration equation. The results showed that the SST seasonality for this 30-year window around AD 1099 was about 3.11 °C, which is smaller than the modern warm period (i.e., about 4.36 °C for AD 1994 ∼ 2005 interval). This new result is consistent with another published Tridacna gigas record that was dated around AD 990 from the northern SCS. The signals of ENSO activity were also extracted from the reconstructed SST record and statistical analyses yielded 9 El Niño events and 8 La Niña events within the 30-year record, indicating that the frequency of ENSO activity around AD 1099 was similar to the modern instrumental period.
... Three lakes in the Andes of Ecuador (Piñan, Yahuarcocha and Fondococha) experienced a coincident peak in LCBDrich, but less in LCBrepl, at ca 1000 cal years BP, likely responding to dry/warm conditions centered around the Medieval Climate Anomaly (MCA). The MCA triggered lower lake levels based on many tropical Andean paleolimnological records (Figure 3; Lüning et al., 2019 and references therein). Despite different conditions in water chemistry and lake depths, our findings suggest that the relatively high synchronous compositional uniqueness at that time may be a fingerprint of regional-scale limnological variation in these three lakes. ...
High-elevation tropical lakes are excellent sentinels of global change impacts, such as climate warming, land-use change, and atmospheric deposition. These effects are often correlated with temporal and spatial beta diversity patterns, with some local communities contributing more than others, a phenomenon known as local contribution to beta diversity (LCBD) or ecological uniqueness. Microorganisms, such as diatoms, are considered whole-ecosystem indicators, but little is known about their sensitivity and specificity in beta diversity studies mostly because of the lack of large spatial and temporal datasets. To fill this gap, we used a tropical South American diatom database comprising modern (144 lakes) and paleolimnological (6 sediment cores) observations to quantify drivers of spatial and temporal beta diversity and evaluated implications for environmental change and regional biodiversity. We used methods of beta diversity partitioning (replacement and richness components) by determining contributions of local sites to these components (LCBDrepl and LCBDrich), and studied how they are related to environmental, geological, and historical human variables using Generalized Additive Models (GAM). Beta replacement time series were also analyzed with GAM to test whether there is widespread biotic homogenization across the tropical Andes. Modern lake ecological uniqueness was jointly explained by limnological (pH), climatic (mean annual precipitation), and historical human density. Local lake (conductivity) and regional geodiversity variables (terrain ruggedness, soil variability) were inversely correlated to replacement and richness components of LCBD, suggesting that not all lakes contributing to broad-scale diversity are targets for conservation actions. Over millennial time scales, decomposing temporal trends of beta diversity components showed different trajectories of lake diatom diversity as response of environmental change: i) increased hydroclimatic variability (as inferred by decreased temperature seasonality) mediating higher contribution of richness to local beta diversity patterns ca. 1000 years ago in Ecuador Andean lakes and ii) lake-specific temporal beta diversity trends for the last ca. 200 years, indicating that biotic homogenization is not widespread across the tropical Andes. Our approach for unifying diatom ecology, metacommunity, and paleolimnology can facilitate the understanding of future responses of tropical Andean lakes to global change impacts.
... The OSL ages obtained for the marine surficial cover sampled at "Praia do Leste" (P3 site) and the model presented, indicate that around 0.980 ± 0.090 ka to 0.780 ± 0.110 ka there was a transgressive event (Souza and Perez Filho, 2019). This transgressive event was likely triggered by a decrease in fluvial discharge and supply of sediment to the coastline, with the geomorphological dynamics established consistent with the Medieval Warm Period (Lüning et al., 2019). ...
The Iguape River estuary – located on the southern coast of São Paulo state (Brazil) – presents geomorphological records of the complex processes operating during the Late Holocene. Dating the top deposits of coastal (fluvial, transition and marine deposits) low terraces, contributes to the understanding of the erosive-depositional events resulting from autogenic and allogenic processes. Optically stimulated luminescence (OSL) dating, grain-size and morphostructural analysis were used to investigate the Late Holocene geomorphological evolution of the Iguape estuary. The results suggest that formation of the Iguape estuary is consistent with a marine incursion triggered by climate pulses by around 2.7 ka. However, the coastline displacement was controlled by base-level adjustments and fluvial incision phases probably induced by fault activity associated with the Guapiara Lineament. Finally, the results show that the estuarine systems in humid tropical regions are significantly sensitive to short time-scale climate events during the Holocene.
... The available reconstructions, which are geographically scattered, have demonstrated significant environmental and climatic changes during the last millennia, mainly related to the Medieval Climatic Anomaly (MCA), the Little Ice Age (LIA), and shifts in the latitudinal position of the westerlies; instrumental studies have also recorded warming conditions during the twentieth century (Barros et al., 2015). Such climatic periods are better established in the Northern Hemisphere; however, temperature reconstructions show warm and cold peaks varying regionally, with more similarity within each hemisphere than between them, without evidence of globally synchronized MCA and LIA intervals (Mann et al., 2009;Ahmed et al., 2013;Neukom et al., 2014;Lüning et al., 2019). ...
Lake sediments are key archives for paleoenvironmental investigation as they provide continuous records of the depositional history of the lake and its watershed. Lake Futalaufquen (42.8°S) is an oligotrophic waterbody located in Los Alerces National Park in the Andes of northern Patagonia, South America. A sedimentary sequence covering 1600 years was recovered to analyze the potential for paleoenvironmental reconstructions of the last millennia. Integration of different geochemical and mineralogical parameters and comparison with climatic reconstructions from other Patagonian records give clues for the identification of a warm period around AD 800–1000, associated with the Medieval Climatic Anomaly. The high frequency of tephra layers beginning in the mid-sixteenth century precludes identification of the Little Ice Age, recorded in northern Patagonia as a cold period from the fourteenth to the eighteenth century. Furthermore, the parameters analysed do not provide evidence of late-twentieth-century global warming. However, Zn deposition, a long-distance atmospheric transport process of anthropogenic origin, was identified during the last century.
... Whereas we observe drier conditions (reduced SASM) and a negative SOIphase (El Niño-like) for the Medieval Climate Anomaly, common interpretations associate the Medieval Climate Anomaly with La Niña-like conditions, while the LIA is often associated with El Niño-like conditions (e.g., Cobb et al., 2003;Denniston et al., 2015;Mann et al., 2009). However, interpretations are still subject to scientific discussions, and even contrary results have been published (Conroy et al., 2008;Lüning et al., 2019;Moy et al., 2002;Martel-Cea et al., 2016;Rustic et al., 2015;Tan et al., 2019;Yan et al., 2011; see Figure S3). Barr et al. (2019) stated that differences in interpretation arise due to heterogenic relationship between terrestrial hydroclimate proxies, oceanic sea surface temperature proxies, and theoretical and physical models of predicted responses to global temperature changes. ...
Plain Language Summary
Stable oxygen isotopes (δ¹⁸Ocell) that are incorporated in cellulose of organic matter of plants accumulated by cushion peatlands on the Puna Plateau are a useful tool to investigate past environmental changes in the southern central Andes. Contemporaneous changes in the composition of δ¹⁸Ocell became evident in the high‐elevation peatlands from Cerro Tuzgle (24°S) and Lagunillas (27°S). Within the last 1,800 years, two distinct fluctuations occurred that can be interpreted as change in the regional precipitation supply which is controlled by the South American summer monsoon (SASM) intensity. According to this interpretation, specifically, high SASM‐activity and, thus, increased precipitation occurred between 1,530 to 1,270 cal. yr BP and between 470 to 70 cal. yr BP whereas SASM‐strength reduced before 1,530 cal. yr BP and between 1,270 to 470 cal. yr BP. Strong support for this interpretation is the high accordance with other SASM‐affected paleoclimatic records of the northern central Andes (10–13°S) and high conformity with the Southern Oscillation Index. This also indicates a persistent impact of the SASM during the last 1,800 years.
... Initially, it was defined as a period of globally increasing temperatures 13 , but over the past decades, several studies, based on temperature-sensitive proxies have reconstructed global and hemispheric temperatures 14 , showing a more complex scenario with rising and decreasing temperatures in different parts of the globe. In South America, this event is most prominently recognized as a dry period over the tropical Andes region, as seen in isotopic records; conversely, in other regions and proxies, its potential impacts are not that well understood 15,16 . ...
The South American Monsoon System is responsible for the majority of precipitation in the continent, especially over the Amazon and the tropical savannah, known as ‘Cerrado’. Compared to the extensively studied subtropical and temperate regions the effect of the Medieval Climate Anomaly (MCA) on the precipitation over the tropics is still poorly understood. Here, we present a multiproxy paleoprecipitation reconstruction showing a consistent change in the hydrologic regime during the MCA in the eastern Amazon and ‘Cerrado’, characterized by a substantial transition from humid to drier conditions during the Early (925-1150 C.E.) to Late-MCA (1150-1350 C.E.). We compare the timing of major changes in the monsoon precipitation with the expansion and abandonment of settlements reported in the archeological record. Our results show that important cultural successions in the pre-Columbian Central Amazon, the transition from Paredão to Guarita phase, are in agreement with major changes in the hydrologic regime. Phases of expansion and, subsequent abandonment, of large settlements from Paredão during the Early to Late-MCA are coherent with a reduction in water supply. In this context we argue that the sustained drier conditions during the latter period may have triggered territorial disputes with Guarita leading to the Paredão demise.
... To better understand and distinguish natural and anthropogenic contributions to the warming and glacier retreat of the last 150 years, the observed climatic change must be placed in a longer-term palaeotemperature context. Of particular interest is the Medieval Climate Anomaly (MCA), a recognized period of natural pre-industrial climate change associated with marked temperature and hydroclimatic variability in many parts of the world (e.g., Graham et al. 2011;Lüning et al. , 2018Lüning et al. , 2019Mann et al. 2009;Seager et al. 2007). The anomaly was first described by Lamb (1965) as "Early Medieval Warm Epoch", which subsequently changed in the literature to "Medieval Warm Period", and later to MCA. ...
Temperatures in Oceania have risen by 0.5–1 °C over the past 100 years, resulting in significant retreat of New Zealand’s glaciers as an example. To better understand natural and anthropogenic contributions to this warming process, the observed climatic change must be placed in a longer-term palaeotemperature context. Of interest is the Medieval Climate Anomaly (MCA, 1000–1200 AD), a recognized period of natural pre-industrial climate change, associated with marked temperature and hydroclimatic variability that is best known from the Northern Hemisphere. Temperature reconstructions for Oceania were traditionally based on two classical tree ring series. Here, we enlarge the Oceania reference data set with another 13 published temperature reconstructions from SE Australia, New Zealand, and West Papua. These are based on a variety of proxy types and help to geographically and methodologically augment the regional palaeoclimate database. The proxy series have been thoroughly compared and the MCA trends palaeoclimatologically mapped. Ten out of the 15 sites show a relatively warm MCA, compared to the last 1500 years, with warming generally occurring in the envelope period 900–1500 AD. In some sites of SE Australia and at the west coast of New Zealand’s South Island, warming appears to be delayed by 200–300 years. The end of the medieval warming at around 1500 AD occurred about two centuries later than on most other continents, suggesting a possible interhemispheric climate lag mechanism possibly involving deep-water circulation. Likely drivers for the medieval warming in Oceania are atmospheric-ocean cycles such as the Southern Annular Mode and El Niño-Southern Oscillation, in combination with solar activity changes. MCA palaeotemperature data are still lacking for large parts of Oceania, namely the arid and tropical parts of Australia, Micronesia, central and northern Polynesia, as well as central and eastern Melanesia, highlighting the need for future research.
Laguna de las Nutrias is a small/enclosed shallow lake located within an environmentally protected area under negligible anthropogenic impact in Southeastern South America (SESA). It holds a high-resolution sedimentary record that allowed us to infer the hydrological response to the regional climatic variability during the last 700 year linked to different climate variability modes. We performed 2 mm-µXRF-scanning analyses on an 88-cm long sediment core, which was dated by both ¹⁴ C and ²¹⁰ Pb techniques. We utilized Ti/Al, Ti/Ca, Fe/Mn, Ti/K, S/Ti, Br/Ti, and Si/Ti as proxies for catchment runoff, lake level, redox conditions, grain size, organic matter, storms/extreme events, and trophic state, respectively. The lowest sedimentation rate, lake level, runoff values, highest trophic state and grain size were recorded between 1360–1800 CE, assigned to the Little Ice Age (LIA), under low humidity conditions related to the weakening of the South American Low-Level Jet (SALLJ). Subsequently, the highest sedimentation rate values, runoff and lake level were recorded up to the present. Concomitant lowest trophic state conditions were inferred and interpreted as dilution processes associated with higher lake levels. This stage was assigned to the onset of the Current Warm Period (CWP), which was characterized by higher humidity conditions leading to the highest sedimentation rate, lake level and runoff values after 1980 CE, associated with the noticeable increase in rainfall during “1970´s climatic shift”. By performing time series analyses, we determined centennial, multi-decadal, decadal, and inter-annual cyclicity in lake level related to the hydroclimatic variability. Furthermore, a high significant positive/negative Spearman correlation was observed between runoff and lake level/trophic state proxies and the El Niño Southern Oscillation (ENSO) reconstruction. ENSO modulates both long and short-term frequency of SALLJ, leading to an increase in rainfall during positive phases, which determined high lake level and runoff and a decreased trophic state due to dilution processes. The reconstructed hydrological variability herein is synchronic with other SESA lacustrine systems and the increased Rio de la Plata discharge, indicating similar long-term limnological responses to the regional climatic patterns.
The Holocene sedimentary record of the Sebkha El Guettiate is located on the southern coast of Skhira, Gulf of Gabès in Tunisia. The cyclostratigraphic study depends on the idea that important segments of the stratigraphic record have recognizably encoded the orbital armature, periodic variations of the terrestrial insolation (Milankovitch cycles). It is a specific method of stratigraphy which studies the succession of different geological strata based on the results of climatology, astronomy and mathematical techniques. Holocene cyclostratigraphy is related to solar activity and other oceanographic and astronomical factors. This study aimed to test the climatic cyclicity along a core of Sebkha El-Guettiate located along the Mediterranean coast in Tunisia, by focusing on the study of the particle size distribution, in particular the variability of the sandy and silty fractions. Based on the dating of Zaibi et al. (2011) they were estimated to cover the last millennia with a sedimentation rate of 0.32 mm/year. This rate accepts the preparation of a depth-age model to perform the spectral analysis.Our analysis found cycles of ≈ 2000, ≈ 1600, 1300, 1000, 800, 595, 324 and 166 years. The 2000 year and 1000 year cycles are related to solar activity. The 1600 years cycle is likely related to internal forcing of the Atlantic Ocean. The 1300-year and 800-year cycles are probably related to the thermohaline circulation of the oceans. However, the other cycles of 600 years 324 years and 166 years are probably related to other oceanographic and atmospheric factors.
Increasing surface air temperatures and
human influences (e.g., agriculture, livestock grazing,
tourism) are altering lacustrine ecosystems in
the South American Andean páramo, and these influences
are evident in changes in the diatom-species
composition in sediment cores from the region that
span the last ~ 150 years. Existing studies are limited
by their short temporal scales and limited spatial
extent. We analyzed two sediment cores spanning
the last two millennia from the northern (Laguna
Piñan) and southern (Laguna Fondococha) Andean
páramo of Ecuador to provide a longer-term perspective
on lake dynamics. Both lakes show shifts in the
dominant diatoms through time. Fondococha diatoms
shifted in dominance between two Aulacoseira species
and in the planktic to benthic ratio, and these
shifts are interpreted as evidence of changing lake
level. The inferred shifts are corroborated by changes
in sediment geochemistry. Piñan shows a directional
shift in the diatom assemblage over the period of the record, from benthic diatoms tolerant of high dissolved organic carbon (DOC), low pH, and low
nutrients, to an assemblage characteristic of lower
DOC, higher pH, nutrients
and lake levels. Shifts in Piñan’s diatoms are correlated
with tephra layers in the sediment, suggesting
that local volcanic deposition may have been responsible
for altering the catchment and lake geochemistry.
This is supported by relatively high δ13C values
in organic matter associated with tephra layers, which
become more negative up-section. Our study suggests
that remote lakes in spatially heterogenous montane
regions act as sentinels of different facets of environmental
change and provide insights into Andean ecosystem
responses to environmental perturbations.
The Ribeira de Iguape estuarine system in Southeastern Brazil has resulted from the complex interactions betweenallogenic (climate, tectonics, and human interventions) and autogenic geomorphological processes. Early studies have shownthat the relationship between sedimentary balances, fluvial discharge, and Holocene climate pulses resulted in the coastlinedisplacement and low fluvial-marine terraces morphogenesis, which are composed of the marine and fluvial sedimentaryunits. In this perspective, this study aimed to investigate whether the microtextural and morphological records on the quartzgrains associated with the different allostratigraphic units (marine and fluvial) correspond to the paleoenvironmentsidentified in previous studies. In this study we have used a combination of analyses (grain-size, microtextural, and absolutedating) applied to the surficial cover sampled from two fluvial-marine terraces located on the right and left banks of theIguape river channel. The results show correspondences between paleoenvironments and microtextures found on the quartzgrains, confirming the statements addressed in previous studies that indicated the coastline was positioned about 9 kminland around 3.5-2.7 ka.
Lacustrine sediments from ice-free areas of Antarctica record both paleoecological and paleoclimatic information. Four sediment profiles (IIL1, IIL3, IIL4 and IIL9) were collected at Inexpressible Island, Ross Sea, to establish a robust late-Holocene chronology using accelerator mass spectrometry (AMS) ¹⁴C dating and geochemical and lithological analyses. The IIL1 and IIL4 sediments were strongly affected by penguin guano, and their bottom (oldest) ages were dated to 1659 and 4860 yr BP, respectively, using a Mixed Marine SoHem mode. By contrast, the organic matter of IIL3 and IIL9 sediments were predominantly sourced from aquatic microbial mats with the bottom ages of these two cores at 3179 and 2945 yr BP, respectively, based on a SHCal13 mode. The mass accumulation rates of the four sediment profiles inferred from this chronology showed peaks during ~1400–800 yr BP, corresponding to greater mean grain size and higher sand fraction ratios in the IIL3 and IIL9 profiles, suggesting strengthened hydrodynamic effect in this period. Our results indicate a relatively warm period occurred in the study area, in accordance with an ‘optimum’ warming in the Ross Sea region. From a regional view, this warm period was also consolidated with climatic records from the western Ross Sea, most likely corresponding to a well-recognized climate perturbation known as the Medieval Climate Anomaly (MCA) in many parts of the world.
In recent years, agriculture in the Andes has shown greater sensitivity to climate change, favoring processes of soil erosion, retreat of glaciers, loss of vegetation cover, increased intensity of rainfall and alteration in the dynamics of crops in the region such as: potato, quinoa, corn, among others. This motivated many authors to develop regional model simulations to estimate the vulnerability index of these agricultural systems to these climatic events, allowing them to provide a more reliable climatological data in the presence of hot and dry winds. In this review article, the main contributions provided by various researchers regarding the impact of climate change on Andean agriculture are detailed. According to the collected information, it is concluded that climate change in the Andes will cause countries such as Brazil, Bolivia, Ecuador, Venezuela, Guyana and Colombia, to increase their local temperature, potential for evapotranspiration and water scarcity, causing the loss of important crops such as rice. In contrast, countries such as Peru, Argentina, Chile, Bolivia and Uruguay will register lower temperatures that will affect their production and yield in crops such as quinoa, potatoes, tarwi, among others. © 2021 Corporacion Colombiana de Investigacion Agropecuaria Corpoica. All rights reserved.
Observações em superfície da temperatura global sobre os continentes e oceanos indicaram um aumento no último século como resposta a eventos cadas vez mais frequentes e intensos de anomalia da temperatura da superfície do mar. Desta forma, o objetivo deste estudo é apresentar as influências exercidas pela Oscilação Multidecadal do Atlântico (AMO) sobre as temperaturas da América do Sul, durante o período de verão austral, para o período de 1901 a 2012. Foi observado que a temperatura do ar apresentou tendências positivas estatisticamente significativas para a região Sudeste e Sul do Brasil. Padrão semelhante foi observado para os extremos de temperatura para todo o período em análise. Ao dividir em períodos conforme a oscilação da AMO, e removendo a tendência, verifica-se que as anomalias das temperaturas do ar são mais acentuadas durante a AMO-, é esperado um aumento (redução) da temperatura do ar e seus extremos principalmente sobre a Bacia do Rio da Prata e Nordeste do Brasil (Centro-Oeste e Sudeste do Brasil). Estes padrões são esperados pelo fato que durante a AMO+ ocorre um aumento da nebulosidade sobre a região correspondente a formação da ZCAS, além de um deslocamento mais para norte da ZCIT, fazendo com que a temperatura do ar fique com menores valores. Por outro lado, no extremo Sul da AS, as anomalias negativas da Tar e Tmin durante a AMO+ estão associadas com o transporte de umidade do Oceano Atlântico Sul pelo centro de alta pressão que se forma no litoral da Argentina.Decadal fluctuations in South American air temperature during the southern summer period and its relationship to the North Atlantic OceanA B S T R A C TSurface observations of global temperature on continents and oceans have indicated an increase in the last century in response to increasingly frequent and intense sea surface temperature anomaly events. Thus, the aim of this study is to present the influences exerted by the Atlantic Multidecadal Oscillation (AMO) on South American temperatures during the austral summer period, from 1901 to 2012. It was observed that the air temperature presented statistically significant positive trends for the Southeast and South of Brazil. Similar pattern was observed for temperature extremes for the entire period under analysis. By dividing into periods as the AMO fluctuates, and removing the trend, it is found that anomalies in air temperatures are more pronounced during AMO-, an increase (decrease) in air temperature and its extremes is expected mainly over the Silver River Basin and Northeast Brazil (Midwest and Southeast Brazil). These patterns are expected due to the fact that during AMO + there is an increase in cloudiness over the region corresponding to the formation of ZCAS, as well as a further northward displacement of the ZCIT, making the air temperature lower. On the other hand, in the extreme south of AS, negative Tar and Tmin anomalies during AMO + are associated with the transport of moisture from the South Atlantic Ocean through the high pressure center that forms off the Argentine coast.Keywords: AMO, air temperature and teleconnection
The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics.
Most reconstructions of the South American Monsoon System (SAMS) over the last two
millennia are based on δ18O records from locations at high-elevation sites in the Andes, which are not
influenced by the South Atlantic Convergence Zone (SACZ). Yet the SACZ is a key driver of SAMS variability
over much of Brazil. Here we use two new δ18O records from speleothems sampled in the central and
southwestern portions of the SACZ core to show that the SAMS was not varying in phase over the entire
tropical continent during the last two millennia. In fact, speleothem records located to the northeast of the
SACZ record precipitation variations that are antiphased with similar records on the opposite side of the
SACZ, in particular during the Little Ice Age period, while records close to the core of the SACZ axis show no
significant departure from the mean state during this period.
The Humboldt coastal upwelling system in the eastern South Pacific ocean is one of the most productive marine ecosystems in the world. A weakening of the upwelling activity could lead to severe ecological impacts. As coastal upwelling in eastern boundary systems is mainly driven by wind stress, most studies so far have analysed wind patterns change through the 20th and 21st Centuries in order to understand and project the phenomenon under specific forcing scenarios. Mixed results have been reported, and analyses from General Circulation Models have suggested even contradictory trends of wind stress for the Humboldt system. In this study, we analyse the ocean upwelling directly in 13 models contributing to phase 5 of the Coupled Model Intercomparison Project (CMIP5) in both the historical simulations and an extreme climate change scenario (RCP8.5). The upwelling is represented by the upward ocean mass flux, a newly-included variable that represents the vertical water transport. Additionally, wind stress, ocean stratification, Ekman layer depth and thermocline depth were also analysed to explore their interactions with coastal upwelling throughout the period studied. The seasonal cycle of coastal upwelling differs between the Northern and Southern Humboldt areas. At lower latitudes, the upwelling season spans most of the autumn, winter and spring. However, in the Southern Humboldt area the upwelling season takes place in spring and the summertime with downwelling activity in winter. This persists throughout the Historical and RCP8.5 simulations. For both the Northern and Southern Humboldt areas an increasing wind stress is projected. However, different trends of upwelling intensity are observed away from the sea surface. Whereas wind stress will continue controlling the decadal variability of coastal upwelling on the whole ocean column analysed (surface to 300 m depth), an increasing disconnect with upwelling intensity is projected below 100 m depth throughout the 21st Century. This relates to an intensification of ocean stratification under global warming as shown by the sea water temperature profiles. Additionally, a divergence between the Ekman layer and thermocline depths is also evidenced. Given the interaction of upwelled nutrients and microscopic organisms essential for fish growth, a potential decline of coastal upwelling at depth could lead to unknown ecological and socio-economical effects.
The pollen record from Lagunas de Mojanda, located at 3748 m a.s.l. (northern Ecuadorian Andes) reflects the vegetation and climate dynamics for the last ca 3400 cal yr BP. Páramo vegetation has been the main vegetation type since the beginning of the record. At Lagunas de Mojanda, from the last ca 3400 to 2200 cal yr BP, grass páramo was well represented mainly by Poaceae (40%) and the occurrence of Valeriana (5%), while montane forest taxa were poorly represented and subpáramo taxa were rare. The vegetation composition suggests cool and humid conditions. Between ca 2200 and ca 1300 cal yr BP, montane rainforest and subpáramo taxa had a higher presence but páramo taxa remained the main vegetation type in the study area, suggesting cool climatic conditions. From ca 1300 to ca 500 cal yr BP, páramo vegetation remained stable, with higher presence of Phlegmariurus and Isoetes, suggesting cool and humid conditions. The last ca 500 cal yr BP generally show lower frequency of montane rainforest and subpáramo taxa. Páramo vegetation reached the highest share, with the presence of Poaceae, Plantago and Ranunculus suggesting a trend of peat bog drying. Fires were present during the whole record, perhaps human-caused, but the study area does not show great disturbance except from ca 1300 to 500 cal yr BP, a period of an evident higher influx of charcoal particles coincidentally with nearby ancient human occupation.
Estimating summer temperature fluctuations over long time scales in southern South America is essential for better understanding past climate variations in the Southern Hemisphere. Here, we developed robust 212-yr long basal area increment (BAI) and δ13C chronologies from living temperature-sensitive Fitzroya cupressoides on the eastern slope of the Northern Patagonian Andes (41°S). After removing the increasing trend from the growth records likely due to the CO2 fertilization effect, we tested the potential to reconstruct past summer temperature variations using BAI and δ13C as predictors. The reconstruction based on δ13C records has the strongest predictive skills and explains as much as 62% of the total variance in instrumental summer temperature (n = 81, p < 0.001). The temperature signal recorded in tree-ring growth is not substantially different to that present in δ13C, and consequently does not provide additional information to improve the regression models. Our 13C-based reconstruction shows cold summer temperatures in the second part of the 19th century and in the mid-20th century followed by a warmer period. Notably, the 20th and the early 21st centuries were warmer (+ 0.6°C) than the 19th century. Reconstructed summer temperature variations are modulated by low-latitude (ENSO) and high-latitude (SAM) climate forcings. Our reconstruction based on δ13C agrees well with previous ring-width based temperature reconstructions in the region and comparatively enhances the low-frequency variations in the records. The present study provides the first reconstruction of summer temperature in South America south of 40°S for the period 1800-2011 entirely based on isotopic records.
The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils, peats, and lake sediments has been shown to correlate with mean annual air temperature (MAAT) and has provided valuable new climate reconstructions. Here we use an improved chromatographic method to quantify the fractional abundances of 5- and 6-methyl isomers in surface sediments from 65 East African lakes spanning temperatures 1.6–26.8 °C, and investigate the relationships between these fractional abundances and temperature, lake pH, and other environmental variables. We find that temperature exerts a strong control on brGDGT distributions, including the relative abundances of 5- and 6-methyl isomers, whereas other environmental variables, including lake pH, are weakly correlated to the fractional abundances of the brGDGTs. The distributions of brGDGTs in our lake sediments differ from those of soils and peats, leading to temperature offsets if soil- and peat-based brGDGT temperature calibrations are applied. We develop new calibrations for MAAT for use in lake sediment based upon the MBT´5Me and Index 1 ratios, as well as a multivariate regression of brGDGT fractional abundances on temperature using stepwise forward selection. We obtain root mean square errors (RMSE) between ~2.1 and 2.5 °C for these calibrations, highlighting the potential for brGDGTs to provide precise temperature reconstructions using lake sediment cores. Calibrations for lake pH perform more poorly, likely due to weak correlations between pH and brGDGT distributions in East African lakes. These results indicate that quantification of 5- and 6-methyl isomers separately in lake sediment can improve paleoclimatic reconstructions.
The Southern Annular Mode (SAM) is the leading mode of atmospheric interannual variability in the Southern Hemisphere (SH) extra-tropics. Here, we assess the stationarity of SAM spatial correlations with instrumental and paleoclimate proxy data for the past millennium. The instrumental period shows that temporal non-stationarities in SAM teleconnections are not consistent across the SH land areas. This suggests that the influence of the SAM index is modulated by regional effects. However, within key-regions with good proxy data coverage (South America, Tasmania, New Zealand), teleconnections are mostly stationary over the instrumental period. Using different stationarity criteria for proxy record selection, we provide new austral summer and annual mean SAM index reconstructions over the last millennium. Our summer SAM reconstructions are very robust to changes in proxy record selection and the selection of the calibration period, particularly on the multi-decadal timescale. In contrast, the weaker performance and lower agreement in the annual mean SAM reconstructions point towards changing teleconnection patterns that may be particularly important outside the summer months. Our results clearly portend that the temporal stationarity of the proxy-climate relationships should be taken into account in the design of comprehensive regional and hemispherical climate reconstructions. The summer SAM reconstructions show no significant relationship to solar, greenhouse gas and volcanic forcing, with the exception of an extremely strong negative anomaly following the AD 1257 Samalas eruption. Furthermore, reconstructed pre-industrial summer SAM trends are very similar to trends obtained by model control simulations. We find that recent trends in the summer SAM lie outside the 5–95% range of pre-industrial natural variability.
The leading mode of atmospheric variability in the Southern Hemisphere is the Southern Annular Mode (SAM), which affects the atmosphere and ocean from the mid-latitudes to the Antarctic. However, the short instrumental record of the SAM does not adequately represent its multi-decadal to centennial-scale variability. Long palaeoclimatic reconstructions of the SAM would improve our understanding of its low frequency behavior and its effects on regional temperature, rainfall, sea ice, and ecosystem processes. In this progress report, we review three published palaeoclimatic reconstructions available for understanding multi-decadal to centennial-scale variability of the SAM. Reconstructions reviewed here show similar patterns of decadal SAM variability during the last two centuries, but earlier centuries are less coherent. Reconstructions clearly maintain similar trends towards more positive SAM states since the onset of significant anthropogenic climate forcing from rising greenhouse gas (GHG) concentrations and ozone depletion and these excursions appear unprecedented over at least the last 500 years. We describe how new multi-proxy reconstructions of the SAM could further improve our understanding of its long-term variability and effects across all geographic sectors of the Southern Hemisphere. Here, we recommend careful selection and development of proxies in SAM-sensitive regions and seasons. In particular, proxies related to cool-season conditions and from the poorly-sampled Indian Ocean sector would allow for a true circumpolar and year-round reconstruction of past SAM variability.
Glaciers in the tropical Andes have been retreating for the past several decades, leading to a temporary increase in dry season water supply downstream. Projected future glacier shrinkage, however, will lead to a long-term reduction in dry season river discharge from glacierized catchments. This glacier retreat is closely related to the observed increase in high-elevation, surface air temperature in the region. Future projections using a simple freezing level height-equilibrium-line altitude scaling approach suggest that glaciers in the inner tropics, such as Antizana in Ecuador, may be most vulnerable to future warming while glaciers in the more arid outer tropics, such as Zongo in Bolivia, may persist, albeit in a smaller size, throughout the 21st century regardless of emission scenario. Nonetheless many uncertainties persist, most notably problems with accurate snowfall measurements in the glacier accumulation zone, uncertainties in establishing accurate thickness measurements on glaciers, unknown future changes associated with local-scale circulation and cloud cover affecting glacier energy balance, the role of aerosols and in particular black carbon deposition on Andean glaciers, and the role of groundwater and aquifers interacting with glacier meltwater. The reduction in water supply for export-oriented agriculture, mining, hydropower production and human consumption are the most commonly discussed concerns associated with glacier retreat, but many other aspects including glacial hazards, tourism and recreation, and ecosystem integrity are also affected by glacier retreat. Social and political problems surrounding water allocation for subsistence farming have led to conflicts due to lack of adequate water governance. Local water management practices in many regions reflect cultural belief systems, perceptions and spiritual values and glacier retreat in some places is seen as a threat to these local livelihoods. Comprehensive adaptation strategies, if they are to be successful, therefore need to consider science, policy, culture and practice, and involve local populations. Planning needs to be based not only on future scenarios derived from physically-based numerical models, but must also consider societal needs, economic agendas, political conflicts, socioeconomic inequality and cultural values. This review elaborates on the need for adaptation as well as the challenges and constraints many adaptation projects are faced with, and lays out future directions where opportunities exist to develop successful, culturally acceptable and sustainable adaptation strategies.
This study presents an investigation on the decadal variability of maximum (Tmax) and minimum (Tmin) air temperature in southern Brazil during the period 1961-2011. Daily data from 26 meteorological stations, obtained from Brazil's National Meteorology Institute (INMET), were used to calculate annual and decadal means and standard deviations. From the annual statistics we computed linear trends in Tmin, Tmax and daily temperature range (DTR). The decadal means were used to compute changes in Tmax and Tmin. Annual anomalies were obtained by removing the climatology for 1961-2011. Results show that most of the region experienced a statistically significant increase in both Tmin and Tmax, i.e. nights as well as days are becoming hotter. The increase in Tmin is however more pronounced than in Tmax, resulting in a decrease in DTR. Of particular notice were the increases in Tmin over the state of Paraná and in Tmax along the southern Brazilian coast. Trends in standard deviations show asignificant increase in the amplitude of variability of Tmin for most of the region's stations. Overall, there was a cooling period during the 1960s and 70s. From the early 1980s until early 90s we observed a sharp and unprecedented warming in both Tmin and Tmax time series. After 1993 the Tmax and Tmin anomalies are relatively smaller in magnitude and, in the last eight years of the record, temperatures remained near the climatological average. These results suggest a halt in the overallwarming trend over southern Brazil after mid-2003.
The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000-1200 AD. Here we present a palaeotemperature synthesis for the MCA in Africa and Arabia, based on 44 published localities. The data sets have been thoroughly correlated and the MCA trends palaeoclimatologically mapped. The vast majority of available Afro-Arabian onshore sites suggest a warm MCA, with the exception of the southern Levant where the MCA appears to have been cold. MCA cooling has also been documented in many segments of the circum Africa-Arabian upwelling systems, as a result of changes in the wind systems which were leading to an intensification of cold water upwelling. Offshore cores from outside upwelling systems mostly show warm MCA conditions. The most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles. Conspicuous cold spikes during the earliest and latest MCA may help to discriminate between solar (Oort Minimum) and ocean cycle (Atlantic Multidecadal Oscillation, AMO) influence. Compared to its large share of nearly one quarter of the world's land mass, data from Africa and Arabia are significantly underrepresented in global temperature reconstructions of the past 2000 years. Onshore data are still absent for most regions in Africa and Arabia, except for regional data clusters in Morocco, South Africa, the East African Rift and the Levant coast. In order to reconstruct land palaeotemperatures more robustly over Africa and Arabia, a systematic research program is needed.
We investigated middle- and late-Holocene hydroclimate patterns in the Colombian Andes using indicators of watershed erosion (lithic abundance), precipitation intensity (% silt), lake-level variability (organic carbon and nitrogen, % sand, and diatoms), and fire frequency (fossil charcoal) from a ~4700-year-long sediment archive from Laguna de Ubaque, a small sub-alpine lake on the eastern flank of the eastern Colombian Andes. Our results indicate reduced precipitation, low lake levels, and increased fire occurrence at Ubaque between 4700 and 3500 cal. yr BP (hereafter BP). Precipitation and lake levels increased abruptly while fire occurrence decreased between 3500 and 2100 BP, with the exception of a 300-year dry phase between 2800 and 2500 BP. Although wetter than the 4700–3500 BP interval, precipitation decreased, lake levels fell, and fire occurrence increased after 2100 BP, but with high-frequency variability. Comparison of the Ubaque results with other Colombian paleoclimate records (e.g. Lakes Fúquene and La Cocha) supports an antiphase pattern of precipitation between the high/interior Andes and frontal slope sites. This spatial pattern of variability is consistent with modern responses to the changes in terrestrial atmospheric convection associated with the so-called ‘dry island’ effect. Further comparison with paleoclimate records from Venezuela suggests that the millennial trend toward increasing frontal slope precipitation is consistent with orbitally induced increases in Andean atmospheric convection. Sub-orbital dry island–like hydroclimate variability suggests that other mechanisms that affect Northern Hemisphere convection may act to enhance or diminish this effect on centennial and shorter timescales.
The southern annular mode (SAM) in the atmosphere and the Antarctic circumpolar current (ACC) in the ocean play decisive roles in the climatic system of the mid- to high-latitude southern hemisphere. Using the time-variable gravity data from the GRACE satellite mission, we find the link between the space–time variabilities of the ACC and the SAM. We calculate the empirical orthogonal functions (EOF) of the non-seasonal ocean bottom pressure (OBP) field in the circum-Antarctic seas from the GRACE data for the period from 2003 to 2015. We find that the leading EOF mode of the non-seasonal OBP represents a unison OBP oscillation around Antarctica with time history closely in pace with that of the SAM Index with a high correlation of 0.77. This OBP variation gives rise to a variation in the geostrophic flow field; the result for the same EOF mode shows heightened variations in the zonal velocity that resides primarily in the eastern hemispheric portion of the ACC and coincided geographically with the southernmost boundary of the ACC’s main stream. Confirming previous oceanographic studies, these geodetic satellite results provide independent information toward better understanding of the ACC–SAM process.Graphical Abstract. .
Every 2–7 years, El Niño events trigger a strong decrease in phytoplankton productivity off Peru, which profoundly alters the environmental landscape and trophic chain of the marine ecosystem. Here we use a regional coupled physical-biogeochemical model to study the dynamical processes involved in the productivity changes during El Nino, with a focus on the strongest events of the 1958–2008 period. Model evaluation using satellite and in situ observations shows that the model reproduces the surface and subsurface interannual physical and biogeochemical variability. During El Niño, the thermocline and nutricline deepen significantly during the passage of coastal-trapped waves. While the upwelling-favorable wind increases, the coastal upwelling is compensated by a shoreward geostrophic near-surface current. The depth of upwelling source waters remains unchanged during El Niño but their nutrient content decreases dramatically, which, along with a mixed layer depth increase, impacts the phytoplankton growth. Offshore of the coastal zone, enhanced eddy-induced subduction during El Niño plays a potentially important role in nutrient loss.
The Brazil and Malvinas (Falkland) currents are two major western boundary currents flowing in opposite directions along the western margin of the South Atlantic Ocean. The Malvinas Current carries subantarctic waters derived from the Antarctic Circumpolar Current northward along the western margin of the Argentine Basin. The Malvinas Current extends vertically from the sea surface to the ocean bottom. The Brazil Current carries subtropical waters southward and is restricted to the upper hundreds of meters. The region of collision of these intense flows is the so-called Brazil-Malvinas Confluence, one of the most energetic regions in the World Ocean. Satellite observations of ocean temperature, color and sea surface height reveal that the Confluence is a region of intense mixing of upper ocean subantarctic and subtropical waters. In-situ observations suggest that this mixing of distinct water masses extends to the deep ocean, where salty, high dissolved oxygen waters originated in the North Atlantic Ocean encounter relatively fresh and poorly oxygenated deep waters from the Antarctic Circumpolar Current. This article discusses the water mass properties and circulation along the western boundary of the South Atlantic, in the Brazil-Malvinas Confluence, and the neighboring ocean.
During the 1980s, a new agricultural frontier arouse in Brazil, which occupied part of the states of Maranhão, Tocantins, Piauí, and Bahia. Currently, this new frontier is known as the MATOPIBA region. The region went through intense transformations in its social and environmental characteristics, with the emergence of extensive areas of intensive agriculture and large herds. The purpose of this research was to study the climatic variabilities of temperature in the MATOPIBA region through extreme climate indexes of ClimAp tool. Data from 11 weather stations were analyzed for yearly air temperature (maximum and minimum) in the period of 1970 to 2012. To verify the trend in the series, we used methods of linear regression analysis and Kendall-tau test. The annual analysis of maximum and minimum temperatures and of the temperature extremes indexes showed a strong positive trend in practically every series (with p value less than 0.05). These results indicated that the region went through to a significant heating process in the last 3 decades. The indices of extreme also showed a significant positive trend in most of the analyzed stations, indicating a higher frequency of warm days during the year.
Links:
https://link.springer.com/epdf/10.1007/s00704-017-2179-5?author_access_token=gAeavCrc2E5pzkxCGy3SKPe4RwlQNchNByi7wbcMAY4PjEpw30KVzpKRrnSi87fXthdeztHhRlD0IWWgrcv8QKYahC9TCjA3SNE4EqhG2e_ekcK-2eMw1KHn8sx_C96seghzWORVBsPyX9pgG47OdQ==
https://link.springer.com/article/10.1007%2Fs00704-017-2179-5
En este trabajo se presenta un estudio paleolimnológico basado en el análisis
de múltiples indicadores en múltiples sitios con el objetivo de reconstruir la historia
evolutiva de cinco lagos someros de la llanura Pampeana (Argentina) desde el Holoceno
medio, y así realizar inferencias paleoclimáticas para esta región. Los cinco lagos
estudiados respondieron sincrónicamente y mostraron el mismo patrón de evolución
paleoambiental durante el Holoceno medio y tardío. Entre los ca. 7.000 y 700-500 años
cal AP, se evidencia una primera fase clara, dominada por carofitas del género Chara, que
cambia a los ca. 700-500 años cal AP hacia una fase turbia dominada por fitoplancton y
con una importante presencia de carofitas sumergidas del grupo de las angiospermas, que
indican fases claras que alternan con el estado turbio general. En la vegetación circundante,
se evidencia un cambio desde una comunidad halófita que indica condiciones salobres
e inestables hacia la comunidad de macrófitas que caracterizan en la actualidad a estos
lagos, por lo cual sugiere ambientes con mayor estabilidad. Durante el Holoceno medio
y por largos períodos (alrededor de 6.500 años) la estabilidad del paisaje se mantuvo
debido a las condiciones climáticas más secas que las actuales, en las que predominaron
fluctuaciones de sequías e inundaciones y/o condiciones de alta evaporación. Estas
fluctuaciones son las que mantuvieron a las comunidades tanto acuáticas como terrestres.
A partir de ca. 2.000 años cal AP el incremento de la diversidad de macrófitas sumergidas
(carofitas y angiospermas) indica mayor aporte de nutrientes y materia orgánica, causado
por un aumento en la intensidad y/o duración de las precipitaciones. A partir de este
momento comienza un cambio gradual que se efectiviza a los ca. 700-500 años cal AP, con
el establecimiento de las comunidades de macrófitas emergentes, flotantes y sumergidas,
características de los sistemas actuales.