CTD profile data collected from the Clarion-Clipperton Zone (CCZ), Pacific Ocean during SMARTEX project expeditions JC241 (2023) and JC257 (2024)

Full-depth CTD profiles collected during RRS James Cook cruises JC241 and JC257 in the Clarion-Clipperton Zone (CCZ), northern equatorial Pacific Ocean, an area likely to be targeted for deep-sea mining for polymetallic nodules in 2023 (JC241) and 2024 (JC257). A Sea-Bird 911plus CTD system was used, mounted on a 24-way stainless steel rosette frame, equipped with 12 x 10-litre Niskin bottles. Too few salinity samples were collected for statistics and verification of sensor trends, therefore none were applied. Post-cruise calibration revealed a 0.00193 deg C positive offset of the temp2 (secondary) temperature sensor; this correction was applied in the final files. Scientific objectives: 1. OMCO 1979 experimental site to estimate mining impact on seabed habitats after 40 years; 2. UK-1 site to understand seasonal changes in seafloor currents and benthic boundary layer processes; 3. Mesoscale eddy structure investigation on the approach to UK1. The data were collected by scientists from the National Oceanography Centre, Southampton, UK, as part of the NERC-funded Seabed Mining And Resilience To EXperimental impact (SMARTEX) project (NE/T003537/1).