Multi-Proxy Evidence Of Southward Migration Of The Intertropical Convergence Zone During Heinrich Stadial 1

Abstract

Heinrich event 1 (H1) and its associated stadial period (HS1) resulted in an aridification in the northern hemisphere subtropics and wetter conditions in the Southern Hemisphere subtropics (Deplazes et al.,2013; Wang et al., 2001). Pluvial periods in Northeast (NE) Brazil (Auler et al., 2004) associated with Heinrich Stadials are characterized by a two-phased increase in rainfall amount and a transition to a wetter and more diverse vegetation regime (Dupont et al., 2010) attributed to a southward shift of the Intertropical Convergence Zone (ITCZ). This two-phased structure is well documented from palynological and sediment core records but lacks the high-precision dating required to fully understand the exact timing and duration of the pluvial period. This issue is shared with IPCC models which have a difficult time characterizing the precipitation response in the tropics to modern climate change. By fully understanding past pluvial responses to climate forcings, climate models and mitigation strategies can be improved.Heinrich tuned growth intervals of speleothems in Toca da Barriguda cave in NE Brazil capture past pluvial periods. This study presents the U-Th dated speleothem record, TBR-14, from Toca Da Barriguda in NE Brail during HS1. The main growth interval of TBR-14 extended from 17,029 ±76 years B.P. (before 1950 A.D.) to 15,850 ±90 years B.P. The record consists of oxygen isotopes (δ18O), trace elements, and confocal fluorescence during the pluvial period. The resulting record reveals the timing and structure of the NE Brazil pluvial anomaly associated with HS1 at an unprecedented resolution and precision. δ18O displays a two-phased shift in values related to the latitudinal range of the ITCZ. The oxygen isotope structure is characterized by an initial wet period lasting until 16,166 ± 61 years B.P (-4 to -6 ‰ ?18O), followed by a wetter period ending at 15,850 ± 90 years B.P (-6 to -8 ‰ ?18O). The onset of the wetter period occurred abruptly with a dramatic drop in ?18O (~1.4‰) in two years. The fluorescent banding structure, prior calcite precipitation (PCP) indices, and phosphorus/calcium (P/Ca) ratios indicate that the transition resulted in the wettest period of NE Brazil during HS1. The isotopic drop occurs, within error, at the same time and rate that China shifts abruptly to a drier climate (Treble et al., 2007). On a broader timescale, PCP indices, P/Ca, and confocal banding depict decreased aridity and precipitation changes. These changes are consistent with the ecological bridge hypothesis, which attributes vegetational changes recorded in regional records for the cause of periodic species exchange between the Atlantic and Amazon Rainforests.