A weaker Agulhas Current leads to more Agulhas leakage

Time series of transports in the Agulhas region have been constructed by simulating Lagrangian drifter trajectories in a 1/10 degree two-way nested ocean model. Using these 34 year long time series it is shown that smaller (larger) Agulhas Current transport leads to larger (smaller) Indian-Atlantic inter-ocean exchange. When transport is low, the Agulhas Current detaches farther downstream from the African continental slope. Moreover, the lower inertia suppresses generation of anti-cyclonic vorticity. These two effects cause the Agulhas retroflection to move westward and enhance Agulhas leakage. In the model a 1 Sv decrease in Agulhas Current transport at 32°S results in a 0.7±0.2Sv increase in Agulhas leakage.

Figure 2: The density of drifter transport (red, 1 Sv contour interval) in the first six months after release for all drifters released in 1986 - 1987 (upper, a mean Agulhas Current transport of 65.4 Sv) and 1988 - 1989 (lower, a mean Agulhas Current transport of 61.0 Sv). The blue lines are the transport-weighted mean trajectories. The bathymetry is shown in gray (1500 m contour interval). The dashed line is the location of the GoodHope line over which the Agulhas leakage is calculated. For lower Agulhas Current transports (1988 - 1989), the current detaches from the continental slope farther downstream. The retroflection is consequently moved westward and Agulhas leakage is increased.