15 Apr 2021

15 Apr 2021

Review status: this preprint is currently under review for the journal OS.

Characteristics and robustness of Agulhas leakage estimates: an inter-comparison study of Lagrangian methods

Christina Schmidt1, Franziska U. Schwarzkopf1, Siren Rühs1, and Arne Biastoch1,2 Christina Schmidt et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Christian-Albrechts-Universität zu Kiel, Kiel, Germany

Abstract. The inflow of relatively warm and salty water from the Indian Ocean into the South Atlantic via Agulhas leakage is important for the global overturning circulation and the global climate. In this study, we analyse the robustness of Agulhas leakage estimates as well as the thermohaline property modifications of Agulhas leakage south of Africa. Lagrangian experiments with both the newly developed tool Parcels and the well established tool Ariane were performed to simulate Agulhas leakage in the eddy-rich ocean-sea ice model INALT20 (1/20° horizontal resolution) forced by the JRA55-do atmospheric boundary conditions. The average transport, its variability, trend and the transit time from the Agulhas Current to the Cape Basin of Agulhas leakage is simulated comparably with both Lagrangian tools, emphasising the robustness of our method. Different designs of the Lagrangian experiment alter in particular the total transport of Agulhas leakage by up to 2 Sv, but the variability and trend of the transport is similar across these estimates. During the transit from the Agulhas Current at 32° S to the Cape Basin, a cooling and freshening of Agulhas leakage waters occurs especially at the location of the Agulhas Retroflection, resulting in a density increase as the thermal effect dominates. Beyond the strong air-sea exchange around South Africa, Agulhas leakage warms and salinifies the water masses below the thermocline in the South Atlantic.

Christina Schmidt et al.

Status: open (until 10 Jun 2021)

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Christina Schmidt et al.

Data sets

Data: Schmidt et al. (2021) Christina Schmidt, Franziska U. Schwarzkopf, Siren Rühs, and Arne Biastoch

Christina Schmidt et al.


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Short summary
We estimate Agulhas leakage, water flowing from the Indian Ocean to the South Atlantic, in an ocean model with two different tools. The mean transport, variability and trend of Agulhas leakage is simulated comparably with both tools, emphasising the robustness of our method. If the experiments are designed differently, the mean transport of Agulhas leakage is altered, but not the trend. Agulhas leakage waters cool and become less salty south of Africa resulting in a density increase​.