Latitudinal Migrations of the Subtropical Front at the Agulhas Plateau Through the Mid‐Pleistocene Transition. Issue 7 (12th July 2021)

• Record Type: Journal Article
• Authors: Cartagena‐Sierra, Alejandra; Berke, Melissa A.; Robinson, Rebecca S.; Marcks, Basia; Castañeda, Isla S.; Starr, Aidan; Hall, Ian R.; Hemming, Sidney R.; LeVay, Leah J.
• Is Part Of: Paleoceanography and paleoclimatology. Volume 36:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-12
• Subjects: Agulhas plateau -- mid‐pleistocene transition -- primary productivity -- sea surface temperature -- southern ocean fronts -- subtropical front; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2020PA004084
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The meridional variability of the Subtropical Front (STF) in the Southern Hemisphere, linked to expansions or contractions of the Southern Ocean, may have played an important role in global ocean circulation by moderating the magnitude of water exchange at the Indian‐Atlantic Ocean Gateway, so called Agulhas Leakage. Here we present new biomarker records of upper water column temperature ( U 37 K' and TEX 86 ) and primary productivity (chlorins and alkenones) from marine sediments at IODP Site U1475 on the Agulhas Plateau, near the STF and within the Agulhas retroflection pathway. We use these multiproxy time‐series records from 1.4 to 0.3 Ma to examine implied changes in the upper oceanographic conditions at the mid‐Pleistocene transition (MPT, ca. 1.2–0.8 Ma). Our reconstructions, combined with prior evidence of migrations of the STF over the last 350 ka, suggest that in the Southwestern Indian Ocean the STF may have been further south from the Agulhas Plateau during the mid‐Pleistocene Interim State (MPIS, MIS 23–12) and reached its northernmost position during MIS 34–24 and MIS 10. Comparison to a Globorotalia menardii ‐derived Agulhas Leakage reconstruction from the Cape Basin suggests that only the most extreme northward migrations of the STF are associated with reduced Agulhas Leakage. During the MPIS, STF migrations do not appear to control Agulhas Leakage variability, we suggest previously modeled shifting westerly winds may be responsible for the patterns observed. A detachment between STF migrations and Agulhas Leakage, in addition to invoking shifting westerly winds may also help explain changes in CO2 ventilation seen during the MPIS. Key Points: We present organic geochemical records of water temperature and primary productivity (1.4–0.3 Million years) from the Agulhas Plateau Our data indicate the Subtropical Front was south of the Agulhas Plateau during the mid‐Pleistocene Interim State (0.9–0.47 Ma) Only the most extreme northward migrations of the Subtropical Front are associated with Agulhas leakage reductions