Dynamics, estimation and impact of South Atlantic inter-ocean exchange

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: De Ruijter, W.P.M., Biastoch, Arne, Drijhout, S.S., Lutjeharms, J.R.E., Matano, R., Pichevin, T., van Leeuwen, P.J., Weijer, W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 1999
• Subjects: Antarctic; Indian; Antarc*; South Atlantic Ocean
• Online Access: https://oceanrep.geomar.de/id/eprint/7455/; https://oceanrep.geomar.de/id/eprint/7455/1/DeRuijter-1999.pdf; https://doi.org/10.1029/1998JC900099

Interocean exchange of heat and salt around South Africa is thought to be a key link in the maintenance of the global overturning circulation of the ocean. It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean. This makes it extremely hard to estimate the inter ocean fluxes. Estimates of direct Agulhas leakage from hydrographic and tracer data range between 2 and 10 Sv (1 Sv = 106 m3 s−1). The average ring shedding frequency, determined from satellite information, is approximately six rings per year. Their associated interocean volume transport is between 0.5 and 1.5 Sv per ring. A number of Agulhas rings have been observed to cross the South Atlantic. They decay exponentially to less than half their initial size (measured by their available potential energy) within 1000 km from the shedding region. Consequently, most of their properties mix into the surroundings of the Benguela region, probably feeding directly into the upper (warm) limb of the global thermohaline circulation. The most recent observations suggest that in the present situation Agulhas water and Antarctic Intermediate Water are about equally important sources for the Benguela Current. Variations in the strength of these may lead to anomalous stratification and stability of the Atlantic at decadal and longer timescales. Modeling studies suggest that the Indian-Atlantic interocean exchange is strongly related to the structure of the wind field over the South Indian Ocean. This leads in the mean to a subtropical supergyre wrapping around the subtropical gyres of the South Indian and Atlantic Oceans. However, local dynamical processes in the highly nonlinear regime around South Africa play a crucial role in inhibiting the connection between the two oceans. The regional bottom topography also seems to play an important role in locking the Agulhas Currents' retroflection. State-of-the-art global and regional “eddy-permitting” models show a reasonably realistic ...