MadEx (Madagascar Experiment) was a research cruise on RRS Discovery with the aims of i) surveying the currents south of Madagascar, ii) deploying moorings, and iii) relating the different biological communities to the physical and chemical conditions (temperature, currents and nutrients). The cruise departed from Durban on 26th January 2005, and returned there on 21st February. An eddy/retroflection signal was seen in ocean colour imagery south of Madagascar, and a "radiator grille" survey pattern adopted. This was achieved with a mixture of SeaSoar tows, CTDs and XBTs, with Jason track 196 being occupied at the time of the altimeter overflight. An array of moorings was also laid along this line, with a McLane Moored Profiler placed 120 km further east. A number of surface drifters were also deployed, including the new Pop-up Ocean Drifters. Numerous underway measurements were made. As well as the shipborne ADCPs and standard instrumentation on the non-toxic supply, surface water samples were taken typically every 2 hours to determine salinity and chlorophyll, and other samples kept for subsequent microscopic and flow cytometry analyses. For zooplankton studies, there were vertical hauls of Bongo nets at half the CTD stations. Extra biological information was provided by the Optical Plankton Counter (OPC), Fast Repetition Rate Fluorometer (FRRF) and the Turner Fluorometer, which were all working well on SeaSoar during the latter part of the cruise. MadEx II (Discovery cruise D302) recovered the moorings 14 months later, and repeated some of the biological and physical measurements along the mooring line; it is the subject of a separate cruise report
