R/V Melville, Agulhas Current Transect cruise, November 2011 – A student’s role

Author Neil Malan aboard the RV Melville (Picture: James Campbell) Mooring operations underway on the RV Melville with a top float being retrieved (Picture: Neil Malan) A CTD is deployed off the Transkei coast (Picture: Neil Malan)

The purpose of the Agulhas Current Transect project is relatively simple – to find out how much water the Agulhas Current carries.

The reality of finding out this piece of information involves three types of instruments. Firstly there are moored instruments, which are deployed at specific positions. A mooring typically consists of a heavy anchor, above which a few kilometres of wire holds current meters at specific depths. This whole ensemble is supported by a combination of floats and glass balls, to give the whole instrument buoyancy so that it will stand upright in the water column.

Data collection

Measuring in this way allows collection of a time-series of what the current does at a particular point in time. The project also makes use of ship-based CTD measurements – a package of instruments lowered from the ship which measures salinity, temperature, oxygen content and currents from the sea surface to the ocean floor. This type of instrument provides detailed data, but is only a ‘snapshot’ of the situation at the time it is sent to the bottom. Satellite imagery will also be used as part of the project, hence the transect line is placed along a satellite ground track, but as this work is not done on the cruise itself, we will not discuss it here.

As students on the cruise, our job is firstly to run the CTD watches (in eight-hour shifts) under the supervision of the CTD technicians from Scripps Institution, who are responsible for the scientific instrumentation and the quality of the data collected. When CTD operations are not underway, we assist the mooring team with their deployments and recoveries, and the servicing of their equipment before it goes back into the ocean for another 18 months. In addition to this, students are also given sections of data to work up and analyse as it is collected.

Multi-faceted learning experience

With students aboard from the Universities of Miami, Southampton and Cape Town, it was an interesting mix of people with a wide variety of academic backgrounds and points of view, making for a very interesting learning experience.

Many thanks to both SAEON and Dr Lisa Beal for the opportunity of being involved in this project.

Neil was funded to participate in the cruise with support from SAEON, UNDP GEF and ASCLME.