Pliocene-Pleistocene evolution of the Agulhas leakage to the Atlantic Ocean
- 1Durham University, Department of Geography, Durham, United Kingdom (erin.mcclymont@durham.ac.uk)
- 2EPOC, UMR-CNRS 5805, 33615 Pessac, Bordeaux, France
- 3Scripps Institution of Oceanography, University of California San Diego, La Jolla, USA
- 4School of Earth and Environmental Sciences, Cardiff University, Cardiff, United Kingdom
- 5Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, USA
- 6INSTAAR- Institute of Arctic and Alpine Research, University of Colorado, Boulder, USA
- 7Lamont-Doherty Earth Observatory, Columbia University, Palisades, USA
The Agulhas leakage is an important contributor to the global thermohaline conveyor system, adding warm and saline subtropical waters from the Indian Ocean to the South-east Atlantic Ocean. It has been proposed that weaker Agulhas leakage occurred during glacial stages, but that leakage was reinvigorated during deglaciations and was, in turn, potentially important for the development of interglacial warmth.
Little is known about the longer-term evolution of Agulhas leakage during the Pliocene and Pleistocene (the last 5.3 Ma). In the Pliocene, the continental ice sheets were smaller in size, and the position and strength of key ocean and atmosphere circulation systems in the South Atlantic region were different. The Pliocene is also characterised by a series of gateway changes which are argued to have affected North Atlantic climate, but the response of the Agulhas leakage system remains unclear. It is also unclear whether the ‘early deglaciation’ signal is a specific component of the late Pleistocene 100 kyr cycles. Identifying how and when this signal developed could have important implications for understanding the impact of ocean circulation changes on the development of the mid-Pleistocene climate transition (MPT) ~1.2-0.6 Ma, when the period of the glacial-interglacial cycles shifted from ~41 kyr to ~100 kyr.
Here we present initial results from a new Cape Basin site (Site U1479, 35°03.53′S; 17°24.06′E), which was recovered by IODP Expedition 361 in 2016 from the western slope of the Agulhas Bank (Hall et al., 2016). We combine reconstructions of sea surface temperatures (using the alkenone-derived UK37’ index) and sea surface salinity (from alkenone dD analysis) with details of planktonic foraminifera assemblages, to identify and understand variability in Agulhas leakage operating across both orbital and longer timescales. There is an overall cooling of ~4°C since the Pliocene, but it is focussed around ~2 Ma and from 1.2 Ma. Orbital scale and longer-term variability in SST, sea surface salinity and Agulhas leakage fauna are also determined, demonstrating that the Agulhas leakage system has evolved across a range of timescales through the Plio-Pleistocene, especially in association with the MPT.
References
Hall, I.R., Hemming, S.R., LeVay, L.J., and the Expedition 361 Scientists, 2016. Expedition 361 Preliminary Report: South African Climates (Agulhas LGM Density Profile). International Ocean Discovery Program. http://dx.doi.org/10.14379/iodp.pr.361.2016
How to cite: McClymont, E., Caley, T., Charles, C., Starr, A., Sanchez Montes, M. L., West, M., Rossignol, L., Hall, I., and Hemming, S.: Pliocene-Pleistocene evolution of the Agulhas leakage to the Atlantic Ocean, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7477, https://doi.org/10.5194/egusphere-egu23-7477, 2023.
