Sea-surface salinity variations in the Northern Caribbean Sea across the mid-Pleistocene transition.

This study aimed at documenting climate changes in tropical area in response to the Mid-Pleistocene Transition (MPT) by reconstructing past hydrologic variations in the Northern Caribbean Sea and its influence on the stability of the Atlantic Meridional 5 Overturning Circulation (AMOC) during the last 940 kyr. Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δ¹⁸O, the difference between the modern and the past δ¹⁸O of seawater (obtained by combining alkenone thermometer data with the δ¹⁸O of the planktonic foraminifera Globigerinoides ruber (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in 10 the studied area are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δ¹⁸O record exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 kyr, indicating increased SSS. At a longer timescale, the Δδ¹⁸O exhibits a shift toward lower values for interglacial periods during the last 450 kyr, when compared to interglacial stages older than 650 kyr. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper interhemispheric temperature gradient and associated with reduced northward cross equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 kyr. Following the MPT, lower salinities during the last five interglacial stages indicate a northernmost ITCZ location, forced by changes in the interhemispheric temperature gradient that is associated with the poleward position of Southern Oceanic Fronts that amplified the transport of heat and moisture to the North Atlantic. These processes may have contributed to amplification of the climate cycles that followed the MPT. [ABSTRACT FROM AUTHOR]