RRS Discovery Cruise Report: Cruise D301B and D302. Indian Ocean, 20 March - 11 April 2006

Abstract

Discovery cruises D301B and D392 were a joint expedition between NIOZ and NOC to study the waters flowing to the west and south of Madagascar. The principal aim of the Dutch component (D301B) was to recover and redeploy moorings from the narrows of the Mozambique Channel at 17ES. These moorings contained current meters, ADCPs and sediment traps, and were accompanied by a high-resolution CTD survey and sea-bed samples taken with the multi-corer. The programme for the UK part (D302) was to recover four moorings from the south of Madagascar, and deploy some drifters. A series of CTDs were run along the main mooring line, and also 3 CTDs were placed in an eddy serendipitously lying in the route between the Dutch and UK mooring sites. Water samples from both D301B and D3002 were analysed for oxygen concentration and nutrient content.

Standard underway measurements (temperature, salinity, fluorescence and ADCP) were taken throughout the cruise. These were augmented by samples taken for biological analysis. Two hourly samples were taken separately for i) fixing and later microscopic analysis, and ii) filtering for HPLC analysis of pigments. A robot sampler was used to take small samples every 20 minutes for picoplankton studies using a flow cytometer. Experiments in the Mozambique Channel looked at the dissolution rate of silica i) through long-term deployment of incubation cages, and ii) by looking at diatom decomposition rates through filtration of large volumes from surface and bottom of CTD cats.

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