Hydrothermal activity and deep-ocean biology of the Mid-Cayman Rise. Underway dataset for cruise JC044 and underway and CTD cast datasets for cruise JC082 dataset https://portal.medin.org.uk/portal/start.php?tpc=006_d0de83a31a45594eba272ce5beef0e2b This dataset consists of underway meteorology, navigation and sea surface hydrography measurements from cruise JC044 and JC082 as well as 7 CTD casts for cruise JC082. Data were collected on two RRS James Cook cruises, JC044 and JC082, covering the Cayman Trough and Mid-Cayman Spreading Centre in the Caribbean Sea. Cruise JC044 took place between March 25th and April 22nd 2010 and cruise JC082 took place between February 6th and March 8th 2013. 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. CTD data were obtained from a Seabird SBE CTD system fitted to a rosette and launched at stations along the cruise track. Data were collected as part of the NERC-funded project “Hydrothermal activity and deep-ocean biology of the Mid-Cayman Rise” which aimed to investigate the world's deepest under-sea volcanic ridge, the Mid-Cayman Rise, to advance understanding of patterns of biodiversity in the planet's largest ecosystem. By studying the geology and hydrography of the world's deepest seafloor spreading centre using established techniques, the project aimed to confirm the geological processes driving the vents and to reveal the evolutionary genetic relationships of their inhabitants to those in vents elsewhere. The project was funded by two NERC standard grants. The lead grant, NE/F017774/1, ran from 15 September 2009 to 01 March 2014, and was led by principal investigator Dr Jonathan TP Copley of University of Southampton, School of Ocean and Earth Sciences. The child grant, NE/F017758/1, ran from 19 July 2009 to 31 December 2013, and was led by Dr BJ Morton of National Oceanography Centre, Science and Technology. Underway navigation, meteorology and sea surface hydrography and CTD datasets have been received as raw files by BODC and are available upon request. 20180518 20171120