The dataset comprises physical, biogeochemical and biological measurements of water column properties. Hydrographic profiles of water temperature, salinity, fluorescence, turbidity, attenuance, dissolved oxygen and photosynthetically active radiation were collected, and were supplemented by measurements of surface ocean (temperature, salinity, fluorescence, attenuance) and meteorological (air pressure, air temperature, humidity, wind, irradiance) properties, as well as bathymetry. A comprehensive water sampling program provided biogeochemical data including measurements of dimethyl sulphide (DMS), dimethylsulphionopropionate (DMSP), nutrients, halocarbons, methylamines, pigments, radiogeochemistry and dissolved organic carbon (DOC). Biological data were also collected, including samples of viruses, bacteria, phytoplankton, micro- and mesozooplankton. Currents throughout the water column were measured both at fixed locations and across the study area, while Lagrangian experiments provided further current data. The datqa were collected in the northern North Sea between 5th June 1999 and 1st July 1999 during RRS Discovery cruise D241. Hydrographic profiles were collected using a conductivity-temperature-depth (CTD) package with attached auxiliary sensors, an undulating oceanographic recorder (UOR), a vessel-mounted acoustic Doppler current profiler (ADCP), moored ADCP and temperature sensors, and a suite of standard underway hydrographic and meteorological sensors. Water samples for biogeochemical and biological analyses were collected from both the underway system and CTD bottles, while nets were deployed to collect zooplankton samples. Plankton samples were supplemented by respiration experiments conducted during the cruise. The Lagrangian current data were gathered from four drifters and a tracer experiment where the distribution of sulphur hexafluoride (SF6) released from the ship was monitored via water samples collected from the CTD and the underway system. A survey of the region was carried out in order to locate an Emiliania huxleyi bloom suitable for the study and the chosen bloom was labelled with the SF6 tracer. The biogeochemical process study followed the patch as it drifted in a SE direction and was eventually subducted under Norweigian coastal water on 26 June. The study aimed to investigate DMS biogeochemistry within a coccolithophore bloom. The research was organised by NERC's Plymouth Marine Laboratory and involved the University of East Anglia, Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Marine Biological Association, Defence Research Agency, and Southampton Oceanography Centre. Data management support for the project is provided by the British Oceanographic Data Centre (BODC). The dataset is available on CD-ROM and can be requested from BODC.