A new improved estimation of Agulhas Leakage using observations and simulations of Lagrangian floats and drifters

A new estimate of Agulhas leakage transport is calculated using profiling floats and drifters. Since Richardson's estimate of 15 Sv in 2007, observations of floats and drifters passing through the Agulhas Current have quadrupled. We find that 13% more drifters leak than floats and that the drifters follow a northward leakage pathway via the Benguela Current compared to the northwestward leakage pathway of the floats at 1000 m depth, a result consistent with Richardson. We simulate the isobaric and profiling behavior of the floats and drifters using two high resolution models and two offline Lagrangian tracking tools, quantifying for the first time, the sampling biases associated with the observed floats and drifters. We find that the isobaric behavior of the floats plays a significant role in the leakage calculated and that the profiling behavior does not. Correcting the observed leakage values at the surface and the intermediate layers for these sampling biases results in an improved Agulhas leakage transport of 21 Sv. Due to these biases and the limited amount of observational data, however, we find a sampling error of 4% in the leakage percentage, translating to roughly 3 Sv. This increase in Agulhas Leakage transport from Richardson’s estimate can mostly be attributed to Sverdrup dynamics and using an Agulhas Current transport at the maximum wind stress curl rather than 32^oS.