Article

The Medieval Climate Anomaly in South America

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  • Institute for Hydrography, Geoecology and Climate Sciences
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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.

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... 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. ...
Article
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.
... 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). ...
Article
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. ...
Article
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.
... 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. ...
Article
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.
... 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). ...
Article
Full-text available
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.
... 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. ...
Article
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). ...
Article
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.
... 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. ...
Article
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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.
... 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). ...
Article
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.
... 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). ...
Article
Full-text available
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.
... 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). ...
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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.
... 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. ...
Article
Temperatures in Oceania have risen by 0.5-1°C over the past 100 years, resulting e.g. in significant retreat of New Zealand’s glaciers. In order to better understand natural and anthropogenic contributions to this warming process, the observed climatic change has to be placed in a longer-term palaeotemperature context. Of particular 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 are enlarging the Oceania reference dataset 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 deepwater circulation. Likely drivers for the medieval warming in Oceania are atmospheric-ocean cycles such as the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO), 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.
... 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 . ...
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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.
... STSW most likely exerted a major influence on these areas because of the prevalence of northeasterly winds (Perez et al., 2017). Climatically, this period is partially related to the MCA (1050 to 700 cal yr BP; 900 to 1250 AD) and to the LIA (550 to 100 cal yr BP; 1400 to 1850 AD), interpreted as times when the SAMS mean state was first significantly weakening (MCA) and afterwards strengthening again (LIA), respectively (Lamy et al., 2001;Vuille et al., 2012;Apaéstegui et al., 2014;Lüning et al., 2018). Climatic conditions derived from these states seem to correlate well with our observations, in which the lowest freshwater input from mainland to the inner Uruguayan continental shelf took place during the MCA, whereas the trend of increase intensity in freshwater input is partially concomitant to the LIA, which would have caused a northward shift of the PPW. ...
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In order to strengthen and update knowledge on climatic, environmental and oceanographic changes on the inner Uruguayan continental shelf, we studied pollen, dinocyst and other non-pollen palynomorph assemblages on the sediment core GeoB13813-4. This core was taken from the Rio de la Plata (RdlP) mud depocenter and its remarkable high sedimentation rate for the last ca. 1000 cal yr BP reflects the high terrigenous supply from RdlP. Most pollen and spores are originated from the RdlP grasslands, the vegetation that covers the lower reaches of the La Plata Drainage Basin (LPDB). They mainly represent the regionally dominant grasslands, but also the riparian forests, Butia yatay palm populations, and the herbaceous-bushy marshes around the mouth of the estuary. Pollen from salt marshes, Atlantic rainforest, and Araucaria forests located in southern Brazil reached the study site, probably transported by coastal ocean currents, whereas pollen from Andean regions would represent a long-distance transport by wind. Changes in both proportion and concentration of freshwater and marine palynomorphs indicate variability in freshwater input to the inner Uruguayan shelf. From ca. 1000 to 230 cal yr BP, significant marine influence of Subtropical Shelf Waters (STSW) was inferred, which was diluted by the freshwater supply from the Uruguayan mainland. This time interval was interrupted between ca. 690 to 575 cal yr BP by an increased freshwater contribution to the study area under the influence of Subantarctic Shelf Waters (SASW). From ca. 230 to 25 cal yr BP, a strong influence of RdlP waters was detected, only followed by another phase of dominant STSW during the past century. Such changes were related to regional climatic variability, i.e., Medieval Climate Anomaly, Little Ice Age and Current Warm Period. After ca. 1960 AD, the anthropogenic impact within the LPDB was clearly evidenced both by eutrophication and the first occurrence of PINUS pollen.
... 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). ...
Article
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.
... Climate variability exerts a direct influence on regional precipitation and continental freshwater supply (Barreiro, 2010;García-Rodríguez et al., 2014, Lüning et al., 2018, on oceanographic processes, and also on sediment transport, resuspension and deposition from the continent to the continental shelf (Lantzsch et al., 2014;Marrero et al., 2014;206 Briceño-Zuluaga et al., 2016;Perez et al., 2016). Large estuaries are responsible for most of the terrigenous material supply into the continental margins, and the associated sediment transport processes mobilize terrigenous chemical elements to the coastal zone and continental margins (Depetris, 1968;Bianchi et al., 2007;García-Rodríguez et al., 2014). ...
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The Río de la Plata estuary (RdlP) and adjacent continental shelf exhibit complex hydrological processes as a result of a highly variable fluvial discharge and associated terrigenous supply, which are primarily controlled by regional climatic forcing in interaction with the oceanographic system. Previous hydrological studies indicate that Little Ice Age and Medieval Climate Anomaly resulted in increased/decreased river runoff due to an enhanced/weakened precipitation regime. This study aims to analyze the cyclicity in the runoffrelated continental supply and the associated climatic oscillation behind it over the past 1,000 cal yr BP. To achieve this, we used a 10-m-long sediment core retrieved from the RdlP mud depocenter, which exhibits an extremely high and fairly constant linear sedimentation rate of 1.1 cm yr-1. We performed continuous 1-cm XRF element intensity scans and performed time series analysis on Fe/K, Ti/Al, Fe/Ca, Ti/Ca and Si/Al ratios, considered as regional proxies for inferring fluvial supply. The most significant cyclicities occur at 215, 192, 115, 100, 49, 47, 37, 35, and 2.5-8 yrs recurrence times. The long-term cyclicity is persistent throughout the whole record for all ratios, and it is probably related to solar forcing, i.e., the 200 yr Vries/Suess cycle, which determines the activity of the South American Monsoon System activity. The shorter climate-related cyclicities (˂100 yr) are probably related to the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation and the El Niño Southern Oscillation climatic modes, and were registered only for Ti/Al, Fe/K and Si/Al ratios. We further identified an intensification of such shorter climate-related cyclicities over the past 500 yr BP. This study provides new evidence that both tropical Pacific and Atlantic SSTs and solar forcing are the main drivers of changes in rainfall over Southeastern South America on interannual to decadal, multidecadal and centennial scales, and thus modulates the RdlP river discharge.
... 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). ...
Article
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.
... 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. ...
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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 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. ...
Article
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.
... 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. ...
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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.
... 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). ...
Article
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
... 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. ...
Article
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.
... 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]. ...
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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.
... 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). ...
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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.
... (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). ...
Article
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.
... 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. ...
Article
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.
... 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). ...
Article
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.
... 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). ...
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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.
... 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). ...
Article
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.
... 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). ...
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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.
... 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 . ...
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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.
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The aim of this study is to examine sedimentary organic matter sources, spatial distribution and temporal variability in a large estuarine system, the Río de la Plata estuary (South America). For this purpose, this work integrates recent and historical carbon and nitrogen isotopes (δ13C, δ15N), total organic carbon, total nitrogen, C/N ratios and sediment grain size analyses along the Río de la Plata estuary. Principal component analysis based on biogeochemical variables and salinity revealed two main biogeochemical contrasting zones, corresponding to the upper and the lower estuary. Such zones are derived from the density gradient observed at the maximum turbidity zone acting as a physical barrier by trapping fine sediments and controlling primary productivity. As a consequence, sedimentary total organic carbon and total nitrogen increase from upper reaches towards lower reaches to attain maximum values under the turbidity gradient due to the presence of fine sediments. On the other hand, C/N ratios display an opposite trend, with higher values in the upper reaches due to a higher influence of continental organic matter. Moreover, Stable Isotope Analysis in R (SIAR) based on δ13C and δ15N reveals that the main organic matter source to the sediment appears to be the continental particulate organic matter and the estimated percentages of terrestrial allochthonous contribution (C3 plants) indicated a decreased contribution towards the lower reaches. The paleoenvironmental analysis shows a change in the sedimentary organic matter composition since 1970 associated to an increased influence of terrestrial organic matter. This trend is related to an increase in the Paraná River flow, which in turn is related to climatic variability (i.e., the polarity change of the Pacific Decadal Oscillation). ResumoO objetivo deste estudo é estimar fontes de matéria orgânica sedimentar, distribuição espacial e variabilidade temporal num grande sistema estuarino, o estuário do Río de la Plata (América do Sul). Este trabalho integra dados atuais e históricos de isótopos de carbono e nitrogênio (δ13C, δ15N), carbono orgânico total, nitrogênio total, relação C/N e granulometria do sedimento ao longo do estuário do Río de la Plata. A análise de componentes principais baseada em variáveis biogeoquímicas e salinidade revelou duas zonas biogeoquímicas contrastantes, correspondentes ao estuário superior e inferior. Tais zonas são definidas por diferenças no gradiente de densidade na zona de turbidez máxima, o qual atua como uma barreira física, causando o aprisionamento de sedimentos finos e influenciando a produtividade primária. Como conseqüência, o carbono orgânico total sedimentar e o nitrogênio total aumentam dos trechos superiores para os trechos inferiores atingindo valores máximos sob o gradiente de turbidez devido à presença de sedimentos finos. Por outro lado, a razão C/N exibe uma tendência oposta, atingindo valores mais elevados no estuário superior devido a uma maior influência da matéria orgânica continental. Os resultados isotópicos de δ13C e δ15N sugerem que a principal fonte de matéria orgânica para o sedimento é a matéria orgânica particulada continental. A contribuição alóctone terrestre (plantas C3) diminui no estuário inferior. A análise paleoambiental mostra uma mudança na composição da matéria orgânica sedimentar a partir de 1970, causada pelo aumento do fornecimento da matéria orgânica terrestre. Essa tendência está relacionada a um aumento no fluxo do Rio Paraná, na sequência de alterações climáticas relacionadas com a mudança de polaridade da Oscilação Decadal do Pacífico.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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We review the history of the South American summer monsoon (SASM) over the past ~2000 yr based on high-resolution stable isotope proxies from speleothems, ice cores and lake sediments. Our review is complemented by an analysis of an isotope-enabled atmospheric General Circulation Model (GCM) for the past 130 yr. Proxy records from the monsoon belt in the tropical Andes and SE Brazil show a very coherent behavior over the past 2 millennia with significant decadal to multidecadal variability superimposed on large excursions during three key periods, the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the Current Warm Period (CWP). We interpret these three periods as times when the SASM's mean state was significantly weakened (MCA and CWP) and strengthened (LIA), respectively. During the LIA each of the proxy archives considered contains the most negative δ<sup>18</sup>O values recorded during the entire record length. On the other hand the monsoon strength is currently rather weak in a 2000-yr historical perspective, rivaled only by the low intensity during the MCA. Our climatic interpretation of these archives is consistent with our isotope-based GCM analysis, which suggests that these sites are sensitive recorders of large-scale monsoon variations. We hypothesize that these centennial-scale climate anomalies were at least partially driven by temperature changes in the Northern Hemisphere and in particular over the North Atlantic, leading to a latitudinal displacement of the ITCZ and a change in monsoon intensity over the tropical continent. This interpretation is supported by several independent proxy archives and modeling studies. Although ENSO is the main forcing for δ<sup>18</sup>O variability over tropical South America on interannual time scales, our results suggest that its influence may be significantly modulated by North Atlantic climate variability on longer time scales. Finally our analyses indicate that isotopic proxies, because of their ability to integrate climatic information on large spatial scales, could complement more traditional proxies such as tree rings or historical archives. Future climate reconstruction efforts could potentially benefit from including isotopic proxies as large-scale predictors in order to better constrain past changes in the atmospheric circulation.