Comparison of three velocity sections of the Agulhas current and Agulhas undercurrent

Lowered acoustic Doppler current profiles (LADCP) from an early March 1995 cruise across the Agulhas Current show a swift, narrow undercurrent flowing northeast along the continental slope. Neither this Agulhas Undercurrent nor the adjacent deep extension of the Agulhas Current are evident from measurements of water properties alone, and their absence from the conventional referencing of geostrophic current estimates biases net southward transport estimates high by several sverdrups. Here we refine the original transport calculation by removing barotropic tides and by estimating instrumental and sampling errors. Two additional LADCP sections, from cruises in late March and June 1995, also show the undercurrent and the deep extension of the Agulhas. Differences in the current structure are evident. The Agulhas Current extends throughout the water column in March, but extends only to 2300 m depth in June. Additionally, the current extends further offshore in March. Of the three available LADCP sections, only those from early March and June have sufficient sampling to calculate the net southward transport of the Agulhas Current and Undercurrent. The two estimates, 78±3 and 76±2 Sv, are nearly identical. Consideration of water properties on density surfaces shows that although the undercurrent carries intermediate water with Red Sea Water influence northward, the bulk of this water mass is flowing southward, away from its source, in the Agulhas Current.