The OSCAR (Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge) data set is an interdisciplinary collection of physical oceanography and geophysics measurements. Data collection took place in the Panama Basin, bounded in the north-west by the Cocos Ridge, by the Carnegie Ridge in the south and by South and Central America in the east and north, respectively. Measurements were collected during RRS James Cook cruises JC112 and JC113 (05/12/2014 to 16/01/2015), RRS James Cook cruise JC114 (22/01/2015 to 08/03/2015) and RV Sonne cruise SO328 (06/02/2015 to 06/03/2015). The project investigated the effect of the cooling of young oceanic crust close to a mid-ocean ridge. It is here that rapid cooling is dominated by hydrothermal circulation of seawater through the crust, which is then discharged into the ocean along the ridge. Once in the ocean, released heated seawater mixes with the ambient cold water to form a plume, which provides a mechanism to lift the densest waters away from the bottom boundary layer. Data were collected using Bottom Pressure Recorder, Acoustic Doppler Current Profiler (ADCP), Magnetotelluric Lander, CTD, Vertical Microstructure Profiler, Synthetic Aperture Radar, Ocean-bottom seismograph and Multibeam echosounder. Measurement of salinity, oxygen and helium were also made and zooplankton samples collected with vertical net casts. This multidisciplinary, collaborative research project was led by Professor Richard Hobbs at the Department of Earth Science, University of Durham, UK and funded by Natural Environment Research Council (NERC) grant NE/I027010/1.

This dataset consists of geophysical and underway measurements collected on FS Meteor Cruise M115 . The cruise ran from 01 April to 28 April 2015 from Kingston, Jamaica to Pointe-a-Pitre, Guadeloupe, collecting data within the Cayman Trough. Swath bathymetry data were collected using a ship-fitted Kongsberg Simrad EM122 multi-beam deep ocean echo sounder, with data collected during the cruise along specific profiles with the aim of filling gaps in existing coverage acquired by RRS James Cook cruise JC044. A total of 170 Ocean-bottom seismograph deployments were made at various stations and depths throughout the duration of the cruise, of which 55 were National Environmental Research Council funded. Gravity data were acquired port-to-port using a Micro-G/LaCoste-Romberg air-sea gravimeter (S-40) mounted on a gyro-stabilised platform, which ran throughout the duration of the cruise. This cruise formed the field component of NERC Discovery Science project ‘Crustal accretion and transform margin evolution at ultraslow spreading rates’ which ran between March 2015 and June 2018. It’s aims were: 1) To study the structure and lithology of the crust at the Mt Dent oceanoc core complex (OCC) on the Mid‐Cayman Spreading Center (MCSC) and determine the relationship between this and the adjacent volcanic domain that also hosts hydrothermal vents and; 2) To investigate how the crust changes as it cools and ages as it spreads away from the ridge axis. The Discovery Science project was composed of Standard Grant reference NE/K011162/1. The project was funded from 23 March 2015 to 30 June 2018, and was led by Professor Christine Peirce (Durham University, Earth Sciences). Data have been received by the British Oceanographic Data Centre (BODC), archived, and are available on request from the BODC enquiries team.