Indian Ocean

Indian Ocean Research Group aboard Leg CD 129The Indian Ocean has not been subject to such intensive oceanographic research as the Atlantic Ocean and thus there is still a great deal to learn about present day and past regimes. A five week cruise on board the RRS Charles Darwin over the summer of 2001 was set up in order to look at sediments and water from the deep western boundary current north and south of Madagascar. Leg CD 129 was organised by a Cambridge group led by Professors Nick McCave and Harry Elderfield. Amongst other goals, the cruise aimed to try to assess the changing vigour and chemistry of deep and intermediate water masses over the last glacial cycle using multiple proxies.

Laura Robinson from the Oxford Isotopes and Environment group participated in this cruise in order to collect water and sediment samples for measurement of Th and Pa isotopes.

Box coring machine for sampling sediment drifts on the sea floorThe box corer in the photograph was deployed when sediment drifts were located on the sea floor. Wherever the sediments were suitable a 6-8m Kasten Corer was also lowered to procure a longer record. The sea floor was generally some 3000 - 4000 m deep and each core takes about 4 hours to be lowered and raised back to the ship.

CTD EquipmentThe CTD pictured has twelve 10-litre bottles and sensors to monitor parameters such as salinity, temperature and density. Physical parameters are measured as the CTD is lowered and the bottles are fired at depths of interest as the winch is raised. A series of 10 litre samples were taken at a range of depths and latitudes to begin to monitor and understand the behaviour of thorium and protactinium in the water column. This tracers have the power to tell us about changes in ocean circulation on a wide range of timescales. Their measurement is difficult because the concentrations in water are extremely low, but new MC-ICP-MS machines are making analysis easier.