Abstract
Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. South of Africa, the eastward turning Agulhas Current sheds Agulhas rings, cyclones and filaments of order 100 km that carry the Indian Ocean water into the Cape Basin and further into the Atlantic. Here, we show that the resolution of submesoscale flows of order 10 km in an ocean model leads to 40 % more Agulhas leakage and more realistic Cape Basin water-masses compared to a parallel non-submesoscale resolving simulation. Moreover, we show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. This indicates that the increase in leakage can be attributed to stronger Agulhas filaments, when submesoscale flows are resolved.
Highlights
Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation
In the upper 2500 m of the Agulhas ring path, in particular light South Atlantic Central Waters, South Atlantic Subtropical Mode Waters, and Antarctic Intermediate Waters show larger salinities in INALT60 compared to INALT20r (Fig. 2a)
Future research should focus on the vertical structure of Cape Basin eddies, submesoscale flows and Agulhas leakage, as well as on the role of smaller mesoscale eddies and small-scale topographic features in the leakage dynamics
Summary
The warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. We show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. A prominent contribution to AL is provided by Agulhas rings[6], which are large mesoscale anticyclones irregularly shed by the retroflecting Agulhas Current (AC) They propagate northwestward through the Cape Basin into the Atlantic carrying the AC water with them. A. Global Drifter Programme surface drifter trajectory (Fig. 1), proves that AC waters can leak into the Atlantic by getting trapped in a shear-edge eddy, being transferred to a lee cyclone, leaving the lee cyclone in the Cape Basin and reach the Atlantic as part of the Good Hope Jet. For this study, the effect of submesoscale flows onto AL is isolated by comparing the two numerical ocean simulations. At around 28∘E, the strength, variability, structure and extent of the Agulhas
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