Two-phased ITCZ-driven upper salinity stratification in the western equatorial Atlantic during Heinrich Stadial 11

The Intertropical Convergence Zone (ITCZ) plays a central role in regulating tropical hydroclimate, with direct implications for water security and economic activity across vast regions. Changes in the latitudinal position of the ITCZ are strongly linked to interhemispheric surface temperature gradient, which is modulated by the Atlantic Meridional Overturning Circulation (AMOC). Past periods of AMOC weakening, such as Heinrich Stadials (HSs), offer valuable opportunities to investigate the ITCZ responses to high-latitude forcing. Here, we present a high-resolution multiproxy reconstruction of upper ocean stratification linked to ITCZ dynamics during HS 11 (ca. 136–129 ka), based on a marine sediment core retrieved from the western equatorial Atlantic (WEA; 1.03°S). Beyond the southward-shift of the Atlantic ITCZ, our data reveal a two-phased structure within HS 11. Early HS 11 (ca. 136–134 ka) shows reduced upper ocean stratification, whereas late HS 11 (ca. 134–129 ka) exhibits enhanced stratification. Independent proxy records applied in this study suggest that these changes in stratification are primarily caused by variations in the upper ocean salinity gradient, with temperature playing a secondary role. Reduced stratification during early HS 11 reflects a stronger than previously recognized southward migration of the mean annual ITCZ, to a position south of our core site. During late HS 11, the ITCZ relaxed from this extreme southern position, enhancing upper ocean stratification at our core site. Our findings provide new insights into the southernmost position of the ITCZ during HSs and highlight the role of salinity in controlling upper ocean stratification in the WEA.

Duke Scholars

Author Paul A. Baker Earth and Climate Sciences