Abstract :
[en] Paleoclimatological field reconstructions are valuable for understanding past hydroclimatic variability, which is crucial for assessing potential future hydroclimate changes. Despite being as impactful on societies as temperature variability, hydroclimatic variability - particularly beyond the instrumental record - has received less attention. The reconstruction of globally complete fields of climate variables lacks adequate proxy data from tropical regions like South America, limiting our understanding of past hydroclimatic changes in these areas. This study addresses this gap using low-resolution climate archives, including speleothems, previously omitted from reconstructions. Speleothems record climate variations on decadal to centennial timescales and provide a rich dataset for the otherwise proxy-data-scarce region of tropical South America. By employing a multi-timescale paleoclimate data assimilation approach, we synthesize climate proxy records and climate model simulations capable of simulating water isotopologs in the atmosphere to reconstruct 2000 years of South American climate. This includes surface air temperature, precipitation amount, drought index, isotopic composition of precipitation amount and the intensity of the South American Summer Monsoon. The reconstruction reveals anomalous climate periods: a wetter and colder phase during the Little Ice Age (g1/4 1500-1850 CE) and a drier, warmer period corresponding to the early Medieval Climate Anomaly (g1/4 600-900 CE). However, these patterns are not uniform across the continent, with climate trends in northeastern Brazil and the Southern Cone not following the patterns of the rest of the continent, indicating regional variability. The anomalies are more pronounced than in previous reconstructions but match trends found in local proxy record studies, thus highlighting the importance of including speleothem proxies. The multi-timescale approach is essential for reconstructing multi-decadal and centennial climate variability. Despite methodological uncertainties regarding climate model biases and proxy record interpretations, this study marks a crucial first step in incorporating low-resolution proxy records such as speleothems into climate field reconstructions using a multi-timescale approach. Adequately extracting and using the information from speleothems potentially enhances insights into past hydroclimatic variability and hydroclimate projections.
Funding text :
We thank Raphael Neukom and one anonymous referee for insightful comments and helpful suggestions which helped in improving the quality of our reconstructions and the manuscript. As this study includes data compiled by the SISAL (Speleothem Isotopes Synthesis and AnaLysis) working group, we thank the Pages2k and Iso2k networks, the working groups of the Past Global Changes (PAGES) project. We thank all authors of previous works that provided model simulation data and proxy record data and those researchers who compiled the proxy record databases. We thank Mariano Morales from CONICET, Argentina, for sharing tree ring data from the South American Drought Atlas and further tree ring collections and Michael Erb and Matt Osman for fruitful discussions about PaleoDA. Nils Weitzel, Beatrice Ellerhoff and Markus Maisch are acknowledged for helpful advice and comments during the elaboration of this projectThis research has been supported by the Deutsche Forschungsgemeinschaft (grant nos. 316076679, 395588486 and 442926051) and the Bundesministerium für Bildung und Forschung through the PalMod project (grant no. 01LP1926C). Nathan J. Steiger is supported by the Israel Science Foundation (grant no. 2654/20). This open-access publication was funded by the Open Access Publication Fund of the University of Tübingen.
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