A New Perspective on Past Export Production in the Subantarctic South Pacific for the Last ∼1.4 Myr

Abstract

Accurate reconstructions of export production in the Subantarctic Zone of the Southern Ocean are crucial for understanding the carbon cycle during Earth's past. However, due to the strong bottom water circulation of the Antarctic Circumpolar Current, sediment redistribution complicates age-model-derived bulk mass accumulation rates (BMAR). Here, we assess export production and its drivers over the past ∼1.4 Myr near the Drake Passage entrance using BMAR of biogenic barium, organic carbon, biogenic opal, calcium carbonate, and iron from sediment core PS97/093-2, all of which are corrected for lateral sediment redistribution (corr-BMAR). To quantify this correction, we explore the relationship between sortable silt as a bottom current strength proxy and 230Th-derived focusing factors as indicators of lateral redistribution of sediments, respectively. Our findings highlight peak Fe input prior and during glacials of the Mid-Pleistocene Transition (MPT), likely driven by enhanced Patagonian weathering. The carbonate record indicates increased deep-ocean corrosivity after around 1 Ma ago and displays a shift in the accumulation pattern post-MPT, with only isolated peaks in some peak interglacials. The high carbonate values during MIS 11 likely relate to Gephyrocapsa coccolithophore propagation, preceded and followed by prolonged carbonate dissolution periods, possibly linked to the Mid-Brunhes Event. After the MPT, productivity proxies respond to glacial and interglacial intensity, with maxima found during MIS 16, MIS 11, MIS 5, and the Holocene, while minima occur during MIS 15–12. Our findings offer insights into long-term productivity dynamics and their relationship to important climatic events over the past 1.4 Myr.