GFI/BCCR Seminar: Agulhas Current variability and its implications for Agulhas salt-leakage and South African terrestrial climates

Margit Simon (School of Earth & Ocean Sciences, Cardiff University, UK):

Agulhas Current variability and its implications for Agulhas salt-leakage and South African terrestrial climates

Abstract
The Agulhas Current is the largest western boundary current in southern hemisphere and transports about 70–78 Sv (1 Sv = 106 m3 s−1) of tropical and subtropical waters along the eastern margin of southern Africa. Every year approximately 5-7 Agulhas rings are shed into the South Atlantic causing a salt anomaly there of ~ +0.2. The northward propagation of these density anomalies to the Norwegian–Greenland Seas have been considered to be important for the stability of the Atlantic Meridional Overturning Circulation on decadal-to millennial timescales. However, the origin of the salt oscillations associated with the ring shedding events in the Indian-Atlantic Ocean Gateway (I-AOG) remains equivocal.

In this study we compare multi-proxy paleosalinity records since the Last Glacial Maximum (LGM) with results of model simulations using the fully coupled Community Earth System Model. The new results imply that periods of higher salinity in the source region do not necessarily suggest that a greater fraction of Indian Ocean water entered the South Atlantic Ocean, as previously inferred from proxy records in the I-AOG. The Agulhas warm water transport influences the climatology in SW Indian Ocean incl. precipitation patterns, hence climates of Southern Africa. Here, a detailed 270,000 year-long record from the southwest Indian Ocean documenting terrestrial climate variability in the KwaZulu-Natal province is presented. Southeast African climate variability reflects both the long-term effect of regional insolation changes driven by orbital precession and the effects associated with high-latitude abrupt climate forcing over the past two glacial-interglacial cycles including events not previously identified. The results show that the southeast African region responded sensitively to both short and long-term climate forcing, amplifying the hydrological signal there as compared to the rest of the African continent.