Agulhas leakage extension and its influences on South Atlantic surface water hydrography during the Pleistocene

B. Nirmal, K. Mohan*, Aradhna Tripati, Beth A. Christensen, P. Graham Mortyn, David De Vleeschouwer, M. Prakasam, K. Saravanan

*Corresponding author for this work

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Abstract

The inter-ocean transfer of warm and salty water through the Agulhas leakage is regarded as a significant factor influencing the South Atlantic's surface and intermediate water hydrography. To evaluate the extension of Agulhas leakage for the past 1.2 Ma, planktonic foraminiferal assemblage from Ocean Drilling Program Hole 1088B, within the vicinity of AL, and Hole 1090B, located south of the significant Agulhas retroflection region, were generated. The Hole 1088B shows higher abundance of tropical and sub-tropical assemblage. The com-bination of Globigerinoides ruber, Trilobatus sacculifer, Globigerinoides conglobatus and Globorotalia menardii has previously been defined as the Agulhas leakage fauna [ALF]. The pulse-like amplification of the ALF record at major glacial-interglacial transitions indicates these were periods of strengthened Agulhas leakage with subse-quent shedding of Agulhas rings and filaments as far as-41 degrees S. From-450 ka, the frontal zone exhibits strong ALF variations with evident increase at glacial-interglacial transitions of Marine Isotopic Stages (MIS) 12, 10, 8 and 6, suggesting vigorous eddy mixing and a shift in the leakage zone towards the subantarctic waters. The migration of the Subtropical Convergence and Neogloboquadrina pachyderma (s) coiling ratios during these glacial-interglacial transitions supports the southward expansion of Agulhas leakage. The ALF record is sup-ported by the delta 18O record of Globigerina bulloides from hole 1088B, which identify a major anomaly at MIS 10, with depleted delta 18O values towards the glacial termination. Simultaneously, the results from Hole 1090B show restricted presence of tropical-subtropical assemblage with their appearance reported only at glacial-interglacial transitions of the MIS 16, 12, 10 and 8. The curtailed ALF index and dominance of the subpolar species N. pachyderma (s) indicate the termination of Agulhas leakage before reaching the Subantarctic zone. The ODP sites chosen for the study reveal the intensification of Agulhas leakage and southward shift of the major leakage zone into the subantarctic zone during the Pleistocene glacial-interglacial transitions.
Original languageEnglish
Article number111447
Number of pages9
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume615
DOIs
Publication statusPublished - 1 Apr 2023

Keywords

  • Agulhas leakage fauna
  • Deglacial warming
  • Oceanic teleconnections
  • Pleistocene
  • Subtropical Convergence

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