This dataset consists of measurements of underway meteorology, navigation and sea surface hydrography. A survey of the Caribbean Sea around Montserrat was undertaken from 03 to 16 December 2007. Data were collected on RRS James Cook cruise JC018. Navigation data were collected using an Applanix POSMV system and meteorology and sea surface hydrography were collected using the NMF Surfmet system. Both systems were run through the duration of the cruise, excepting times for cleaning, entering and leaving port, and while alongside. These cruises formed the field component of NERC project "The impact of submarine diagenesis of tephra on seawater chemistry". The objective of the research was to test the hypothesis that early diagenetic alteration of recent, subaerial, volcanogenic material in the submarine environment has a significant impact on the global biogeochemical cycles. A secondary objective was to map the distribution of volcanogenic material in the upper 1 metre of sediments around the island of Montserrat. The Discovery Science project was composed of Standard Grant reference NE/D004020/1 as the lead grant with child grant NE/N001125/1. The grant ran from 24 July 2007 to 23 December 2009 and is held by the University of Southampton, School of Earth and Ocean Sciences. The project was led by Professor Martin Ralph Palmer with co-investigators Professor Damon Andrew Teagle and Professor Rachel Ann Mills. The underway discrete salinity samples data and the underway navigation, meteorology and sea surface hydrography data have been received by BODC as raw files from the RRS James Cook, processed and quality controlled using in-house BODC procedures and will be made available online in the near future. No further data are expected from this cruise.