Observations of strong ocean current events offshore Pemba, Northern Mozambique

Abstract

ABSTRACTThree years (2008–2011) of current measurements outside Pemba (∼13°S), Mozambique, are presented. Oil and gas reserves are found in the region, and knowledge of the ocean current climate is important for safe offshore operations. The full-depth current profile at Pemba was estimated by comparing with moorings further south. The moored record was also compared with geostrophic velocities obtained from sea surface height (SSH) fields, current profiles from ship-mounted Acoustic Doppler Current Profiler and surface currents from seven drifters passing the mooring. Velocities up to 60 cm/s were observed at 850 m depth. Altimetry-derived currents, while strong (often > 100 cm/s), are probably underestimates due to coarse resolution. Direct observations show surface currents up to 170 cm/s. Four strong current events were studied in detail. Three of the four events appeared to be associated with anticyclonic eddies nearby. The time series of SSH-derived geostrophic current always showed southward velocities, never below 20 cm/s. These findings indicate that currents off Pemba may display characteristics of a western boundary current rather than being completely dominated by eddies. Strong current events are probably caused by anticyclones interacting with the boundary current and speeds on the order of 200 cm/s can be expected.