Evidence of Late Pleistocene Heinrich Stadials in Northeastern Brazil

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Evidence of Late Pleistocene Heinrich Stadials in Northeastern Brazil

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Quaternary paleoclimatology is an ever-expanding field. The last glacial period has been characterized by temporally small-scale periods of warming and cooling. Long-term climate oscillations have been attributed to solar forcing, while the cause of these more frequent oscillations are of greater debate. One such cycle is characterized by periods of extreme cooling that triggered freshwater and iceberg excursions into the North Atlantic. The massive release of freshwater and ice into the North Atlantic is thought to have caused an abrupt global reorganization of the ocean-atmosphere circulation. These extreme cooling events are named Heinrich Stadials. Paleoclimate studies have sought to better understand the climatic response to North Atlantic cooling events across the world. In the case of Heinrich Stadials, understanding the response of the hydroclimate throughout the world, and the relationship between local responses, is essential to further our understanding of Heinrich Stadials and their possible causes. In the ocean-atmospheric circulation changes related to Heinrich Stadials, the position of the Intertropical Convergence Zone (ITCZ) plays a pivotal role. Paleo-records suggest that the cooling in the North Atlantic associated with Heinrich Stadials triggered a southward migration in the ITCZ, a response consistent with altering ocean-atmospheric circulation due to influx hemispheric and ocean cooling. Likewise, a shift in the ITCZ could result in a shift in the location and amount of tropical precipitation. Here, we reconstruct one such paleo-record to continue the global reconstruction of climatic response to Heinrich Stadials. Semi-arid Northeastern Brazil is located south of the modern-day ITCZ position. However, large numbers of speleothems in Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves in Northeastern Brazil suggest that there were periods of intense rainfall. One possible source of this past rainfall is a southern migration of the ITCZ. Previous studies have linked short-lived speleothem growth in both caves to Heinrich Stadials (X. Wang et al., 2004; Wendt, 2015). In the following chapters, we present chronologies from 5 distinct periods: 134.8 kyr-130.2 kyr, 72.5 kyr- 71.6 kyr, 66.5 kyr-59.7 kyr,54.9 kyr-54.8 kyr and 48.9 kyr-48.2 kyr. This high-resolution, absolute dated, multi-stalagmite oxygen isotope record considers the hydroclimate of Northeastern Brazil. The main record herein extends through the latter portion of Marine Isotope Stage 4, including HS-6, spanning from 66.4 to 59.7 kyr. We have dated three stalagmites using the U/Th method, with uncertainties in age of average ±0.2 kyr. Growth is continuous in TBV-63 from 62.7 to 59.7 kyr, in TBV-67 from 63.6 to 59.7 kyr and in TBV-34 from 66.4 to 63.0 kyr, with a growth hiatus between 64.8 and 64.0 kyr, within error of Greenland Interstadial (GIS) 18. Immediately following this hiatus, TBV-34 shows an abrupt drop in δ18O values, implying a rapid increase in rainfall likely related to southward migration of the ITCZ associated with stadial conditions in the North Atlantic. The δ18O record of these NE Brazil stalagmites is largely anti-phased with the East Asian Monsoon (EAM). Due to the steady decrease in δ18O values until 59.7 kyr and the correlation with the weak monsoon interval, we infer that rainfall over the cave site steadily increased during the prolonged stadial. An abrupt increase in δ18O values marks the end of growth in these samples and is synchronous within uncertainties with the strengthening EAM at 59.8 kyr, which marks the beginning of GIS-17 and Chinese Interstadial (CIS) 17. The anti-phase relationship between these distant, low-latitude caves supports the hypothesis of a southward migrating ITCZ sensitive to abrupt North Atlantic climate anomalies, and suggests a rapid teleconnection of atmospheric signals during HS-6.


University of Minnesota M.S. thesis.November 2018. Major: Earth Sciences. Advisor: Richard Edwards. 1 computer file (PDF); x, 114 pages.

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Berry, Akemi. (2018). Evidence of Late Pleistocene Heinrich Stadials in Northeastern Brazil. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/201732.

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