The growth intervals of stalagmites from Northeast (NE) Brazil provide precise information on the timing of pluvial periods associated with the southward shift of the Intertropical Convergence Zone (ITCZ) during Heinrich Stadials (HS). Using 230 Th dating and annual band counting, we constrained the timing of the pluvial period associated with HS4 to occur between 40.06 ± 0.11 and 38.38 ± 0.10 thousand years before present (kyr B.P.), coinciding with the interval between the end of Greenland Interstadial (GIS)/Chinese Interstadial (CIS) 9 and GIS/CIS 8. Oxygen isotope analysis shows a close anti-correlation between NE Brazil wet periods and East Asian monsoon intensity recorded in Hulu Cave, supporting the hypothesis of a southerly migration of the global ITCZ during HS4. The pluvial anomaly can be divided into three phases, starting with a precursor, less intense pluvial interval (phase 1) between 40.06 ± 0.11 and 39.59±0.10 kyr B.P., likely correlative to the cool phase of the North Atlantic immediately before the partial collapse of the Laurentide Ice Sheet (LIS). This phase ends abruptly (<30 yr) and is followed by an intense pluvial phase (phase 2) that spans approximately 5 centuries. Luminescent couplets are identified in all samples between 39.50 ± 0.10 and 39.41 ± 0.10 kyr B.P., and are interpreted as a period of two rainy seasons per year during which the southernmost extent of the inland West Atlantic ITCZ reached south of our study site (10°S). Following the end of phase 2 at 39.07 ± 0.32 kyr B.P., intermittent speleothem growth suggests intermittent rainfall over NE Brazil (phase 3) until the abrupt onset of GIS/CIS 8 at 38.38 ± 0.10 kyr B.P. The phases identified in NE Brazilian stalagmites agree with the three-phased variation in low-latitude proxies registered in Northern Greenland, and are consistent with changes in methane concentrations recorded in the West Antarctic Ice Sheet (WAIS) Divide. The synchronicity of these distant records suggests a multi-phased response of tropical atmospheric circulation during HS4. The timescales surrounding the LIS collapse, as inferred from our precisely dated stalagmites, are on the same order as recent predictions for the impending collapse of the WAIS and may therefore serve as a past analogue.
Bibliographical noteFunding Information:
We thank the members of Grupo Bambui de Pesquisas Espeleologicas for their assistance in cave sampling under the permission of IBAMA/CECAV. We thank the UMN Characterization Facility and University Imaging Center for their support in data collection. We thank D. McGee and one anonymous reviewer for constructive comments that greatly improved this manuscript. This research was supported by the National Science Foundation (NSF 1337693 , 1702816 , and 1103403 ). H.C. acknowledges the support by National Natural Science Foundation of China (NSFC 41731174 ). X.W. acknowledges the support by a Singapore National Research Foundation Fellowship ( NRFF2011-08 ). Oxygen isotope data and CFLM images are available for download at the NOAA paleoclimate database.
- Heinrich Stadial
- NE Brazil
- luminescent couplet
- pluvial phase