Latitudinal Migrations of the Subtropical Front at the Agulhas Plateau across the Mid-Pleistocene Transition
Abstract
Latitudinal migrations of the Subtropical Front (STF) at the Indian-Atlantic Ocean gateway control changes in the spatial extent of the Southern Ocean and the magnitude of heat and salt transferred via Agulhas Leakage to the Atlantic Ocean. Expansions of the Southern Ocean have important implications for the air-sea balance of CO2 and meridional overturning circulation. Despite the importance of the region to global climate, STF migrations are still relatively poorly constrained across the mid-Pleistocene transition (MPT). New cores from IODP Site U1475 (41°25.61'S; 25°15.64'E in 2669 m water depth) were recovered by Expedition 361 ('Southern African Climates') in 2016. Site U1475 is located on the southern Agulhas Plateau, an area between the cold, nutrient rich waters of the Sub-Antarctic Zone and the warmer, nutrient poor Agulhas Current waters. Here we present records of water temperature (Uk'37 and TEX86) and primary productivity (chlorins and alkenones), spanning ca. 1.2 to 0.3 Ma.The Uk'37 index is based on C37 alkenones produced by haptophyte algae that live in the photic zone, while TEX86 is based on isoprenoid membrane lipids made by Thaumarchaeota that likely live in the shallow subsurface. Chlorins are diagenetic products of chlorophyll and represent changes in the total phytoplankton community, while abundances of long-chain alkenones represent changes in only haptophyte productivity. Our reconstructions highlight glacial-interglacial variability, showing more abrupt and higher amplitude cycles after the MPT. Temperature and productivity records of the upper water column are strongly coherent, suggesting that primary productivity at the Agulhas Plateau is promoted by the close presence of STF during glacial periods. These records also provide evidence of abrupt southward displacement of the STF during glacial terminations, especially terminations preceding strong interglacials. Our results suggest that the presence of the Agulhas System in the Southwestern Indian Ocean may constrain the latitudinal extent of meridional migrations of the STF in the region.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP52A..04B
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 0732 Icebergs;
- CRYOSPHERE;
- 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY;
- 4910 Astronomical forcing;
- PALEOCEANOGRAPHY