Abstract
The modern state of the Atlantic meridional overturning circulation promotes a northerly maximum of tropical rainfall associated with the Intertropical Convergence Zone (ITCZ). For continental regions, abrupt millennial–scale meridional shifts of this rainbelt are well documented, but the behavior of its oceanic counterpart is unclear due the lack of a robust proxy and high temporal resolution records. Here we show that the Atlantic ITCZ leaves a distinct signature in planktonic foraminifera assemblages. We applied this proxy to investigate the history of the Atlantic ITCZ for the last 30,000 years based on two high temporal resolution records from the western Atlantic Ocean. Our reconstruction indicates that the shallowest mixed layer associated with the Atlantic ITCZ unambiguously shifted meridionally in response to changes in the strength of the Atlantic meridional overturning with a southward displacement during Heinrich Stadials 2–1 and the Younger Dryas. We conclude that the Atlantic ITCZ was located at ca. 1°S (ca. 5° to the south of its modern annual mean position) during Heinrich Stadial 1. This supports a previous hypothesis, which postulates a southern hemisphere position of the oceanic ITCZ during climatic states with substantially reduced or absent cross-equatorial oceanic meridional heat transport.
Highlights
The Intertropical Convergence Zone (ITCZ) can be defined as a narrow belt of maximum tropical precipitation associated with the ascending branch of the Hadley circulation[1]
The resulting shallow tropical mixed layer together with the elevated productivity is recorded in the composition of planktonic foraminifera faunas in the seafloor sediments below, which could be used to track the mean position of the oceanic counterpart of the ITCZ in the equatorial Atlantic
Since the tropical sea surface temperature (SST) gradient modulates the meridional migration of maximum tropical precipitation associated to the ITCZ4, some studies have reconstructed the tropical SST gradient as well as sea surface salinity changes in order to estimate the past position of the Atlantic ITCZ17, 18
Summary
Since more than 70% of the planktonic foraminifera species present in both cores (i.e., Globigerinoides ruber, G. sacculifer, G. glutinata and Globigerinella siphonifera) inhabit the upper 60 m of the water column[42,43,44], we extracted and calibrated the modern annual temperature values for 50 m water depth from WOA 200929. This allowed us to assess subsurface temperatures directly affected by the Atlantic ITCZ (Fig. S2b). Full Methods and any associated references are available in the online version of the paper at www.nature. com/nature
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