A preliminary report on long-term bottom-current measurements and sediment transport/erosion in the Agulhas Passage, southwest Indian Ocean

Abstract

Continuous measurements of bottom-current velocity, direction and temperature are reported from two sites in the Agulhas Passage, SW Indian Ocean. These are the first long-term records from the Indian Ocean: site 1, 4850 m, 262 days and site 2, 4690 m, 356 days. They show fluctuating bottom-current movements with periods between 4 and 40 days and marked contrasts in average velocities and direction: site 1–20 cm s −1 with a NNW progressive vector; site 2–5.5 cm s −1 with a NNE progressive vector. Preliminary examination of the data suggest that the periodic fluctuations in direction and strength may be related to eddies in the overlying Agulhas Current, but also points to a NNE movement of Antarctic Bottom Water in the Agulhas Passage along its northern side. Both sites appear in seismic records as areas of erosion or non-deposition, and whilst the current meter data support this conclusion at site 1 on the southern side of the Passage, data from site 2 suggest that along the foot of the SE African continental margin no sediment erosion or transportation is likely except during short periods (8 hrs.) when the currents are temporarily capable of transporting material up to 200 μm and eroding unconsolidated silt and fine sand.