Climatological Pathway of Agulhas Leakage: Fluxes and Transformations Through the Cape Basin

Abstract

Agulhas Leakage provides a major return pathway through which warm, salty Indian Ocean waters enter the South Atlantic (SA), influencing the Atlantic Meridional Overturning Circulation (AMOC). Quantifying its volume, heat, and salt fluxes is challenging because leakage occurs within a highly turbulent region where Agulhas waters mix with cooler, fresher South Atlantic waters. Using a 20‐year Argo climatology (2002–2022), we identify a persistent Leakage Pathway connecting the Agulhas Current (AC) to the South Atlantic and quantify water‐mass transformations along it. Strong lateral mixing between the Agulhas Retroflection and the Good Hope Line substantially cools ( PW) and freshens central and intermediate waters. As a result, the total transport along the Leakage Pathway (above ) is Sv, carrying PW and Sv psu into the SA, reflecting a mixture of Agulhas and entrained South Atlantic waters. A water‐mass fraction analysis separates the Agulhas Leakage, indicating that the AC contributes Sv, PW, and Sv psu. Upstream of the Good Hope Line, intense eddy activity, topographic interactions, and filamentation drive the strongest cooling and freshening of leakage waters. Observed increases in eddy kinetic energy in the Agulhas system suggest that lateral cross‐stream mixing may increase, further cooling and freshening leakage waters. As leakage volume does not show a significant long‐term trend, water‐mass transformations may reduce the heat and salt transport in the upper limb of the Atlantic Meridional Overturning Circulation.