Ocean currents typically range between 10 – 50 cm/s. Outside Pemba, however, vessels have experienced strong south-flowing currents when trying to enter the port. These could not be explained as tidal currents, because the bottom depth is more than 1000m and therefore tidal currents are weak.
Experimental oil drilling at 1000m depth is planned in the area, which is another reason to learn about the local ocean currents. So a team of scientists from the Instituto de Investigacao Pesqueira, Moçambique and the Universitetet i Bergen, Norway deployed a current meter mooring at about 1000m depth (photo: preparing and deploying the mooring).
This instrument has an internal data recorder, so we have to pick the mooring up again next year to get access to the data.
During the deployment we recorded current speeds using the ship mounted current meter (ADCP) of almost 2 m/s (= 4 knots, almost the speed of a fishing vessel)! If this turns out to be a typical current speed this is bad news for the oil companies, because the currents would cause too high a load on both the drilling platforms and the 1000m long pipes from the surface to the bottom, for present technology to cope with. We will know next year.
Written by Tor Gammelsrød (photos: Tammy Morris)