Abstract
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 Th-230 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="" degrees="" 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="">