Pluvial Period over NE Brazil linked to Heinrich Stadial 4

Thursday, 18 December 2014
Kathleen A Wendt1, Anamarie Häuselmann2, Dominik Fleitmann2,3, Xianfeng Wang4, Augusto S Auler5, Hai Cheng1,6 and R. Lawrence Edwards1, (1)University of Minnesota Twin Cities, Dept. of Earth Sciences, Minneapolis, MN, United States, (2)University of Bern, Institute of Geological Sciences and Oeschger Center for Climate Change Research, Bern, Switzerland, (3)University of Reading, Department of Archaeology, Reading, United Kingdom, (4)Earth Observatory of Singapore, Singapore, Singapore, (5)Universidade Federal de Minas Gerais, CPMTC, Instituto de Geociencias, Belo Horizonte, Brazil, (6)Xi'an Jiaotong University, Xian, China
The precise timing and duration of Heinrich Stadials (HS) remains a topic of active debate. Here we present multiple NE Brazilian stalagmites known to grow during HS 4[i]. Using a combination of U/Th dating, confocal microscopy, and stable isotope analysis, we aim to provide additional age constraints on the Brazilian pluvial anomaly associated with HS 4. Stalagmite growth in this region is caused by increased rainfall due to a southerly displacement of the Intertropical Convergence Zone during HS Events. We focus on three stalagmites—TBV40, TBV63, and TBR14—collected from Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves[ii], respectively. TBV40 and TBV63 each contain an aragonite phase U/Th dated from 40.02 to 39.57 ka B.P., followed by a calcitic phase U/Th dated from 39.27 to 38.74 ka B.P., within errors of ±0.1 ka. The switch from aragonite to calcite at approximately 39.57 ka B.P. is characterized by an abrupt 4‰ decrease in the δ18O record of TBV40. We infer that rainfall increased over NE Brazil at this time. TBR14 has a single calcite growth phase from 39.66 to 39.45 ka B.P., which correlates in part with the calcite phases of TBV40 and TBV 63. Stable isotope values for TBR14 are similar in range, trend, and absolute values to the correlative calcite portion of TBR40. Fluorescent banding was discovered in the calcitic portion of all three stalagmites using confocal laser scanning microscopy. If annual, band-counts may add additional constrains to the duration of the HS 4 growth phases. Adopting ice core band-counting methods, an average of 325±128 bands per sample and 17 small hiatuses were identified. The estimated duration of the calcitic HS 4 growth phases is therefore consistent with the U/Th dates. Growth phases may correlate in detail with other global records of HS 4, such as the Hulu Cave record[iii]from China, with the aragonitic portion correlating to the weak monsoon immediately following Chinese Interstadial 9 and the calcitic portion correlating with the subsequent yet weaker monsoon.

[i] Wang et al. (2004) “Wet periods in northeastern Brazil over the past 210 kyr linked to distant climate anomalies” Nature 432, 740-743

[ii] 40o51’39”W 10o09’36”S

[iii] Wang et al. (2001) “A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from Hulu Cave, China” Science 294, 2345