Glacial-Interglacial climate variability in the Subtropical Atlantic: Evidence from alkenone-based SST records at ODP Site 1058

Feedback mechanisms linked to ocean circulation, ice sheets, and the carbon cycle are key drivers of Quaternary climate variability, especially during glacial periods and transitions. These processes provide critical insights into potential future climate dynamics under ocean warming. This study focuses on two intervals: 410-490 ka (including MIS 12, ~428-468 ka) and 600-700 ka (among MIS 16, ~624-678 ka). We aim to investigate changes in ocean circulation during major glacial periods (MIS 12 and MIS 16) and explore the East-West thermal gradient in the subtropical Atlantic, and its impact on Subtropical Gyre (STG) dynamics within the broader context of global climate systems, by reconstructing sea surface temperatures (SSTs) for these key periods. Samples were taken from cores U1058B and U1058C (2984 meters below sea level) from Ocean Drilling Program (ODP) Site 1058 on the Blake Outer Ridge (BOR), under the strong influence of the Gulf Stream, affecting SSTs. A total of 185 samples were processed using alkenone-based analysis to reconstruct SSTs. Alkenones were extracted from 2.5-2.6 g of sediment, identified, and SSTs were reconstructed using the alkenone U^k'₃₇ index, applying the calibration equation of Müller et al. (1998). Our results reveal a significant SST decrease during the inception to the glacial (~23°C to ~18°C and ~23.5°C to ~19.5°C, at the onset of MIS 12 and MIS 16, respectively). The long term, SST variability displays a cyclicity of around 20-23 ka, with relatively warm/cold episodes that parallel changes in the precessional signal. The glacial-interglacial transitions (Termination V ~428 ka and VII ~624 ka) show contrasting signals: a rapid SST rise during Termination V (~18°C to ~22.5°C), driven by strong increase / maximum precession and obliquity signal, and a more gradual warming during Termination VII (~20°C to ~23.5°C), following obliquity signal. These findings provide valuable insights into Subtropical Gyre dynamics during MIS 12 and 16, enhancing our understanding of past ocean circulation.

This work, part of the Hydroshifts project (PTDC/CTA-CLI/4297/2021) funded by the Foundation for Science and Technology (FCT), used samples from ODP Expedition Leg 172.