RAPID report for RRS Discovery Research Expedition DY174, 28th March 2024 to 3rd April 2024

The purpose of RRS Discovery research expedition DY174 was to refurbish the Eastern Boundary of the RAPID 26°N array of moorings that span the Atlantic from the Bahamas to the Canary Islands. The expedition started in Santa Cruz de Tenerife on Thursday 28th March 2024 and ended on Wednesday 3rd April 2024 at Santa Cruz de Tenerife. The moorings are part of a purposeful Atlantic wide array that observes the Atlantic Meridional Overturning Circulation and the associated heat and freshwater transports. The RAPID-MOCHA-WBTS array is a joint UK- US programme. During DY174 moorings were serviced at sites: EBH3, EBH3L, EBH2, EBH1, EBH1L. A new mooring was deployed at EBH3B as a backup for EBH3. Sites with suffix ‘L’ denote landers fitted with bottom pressure recorders. Moorings were equipped with instruments to measure temperature, conductivity and pressure, and a number of moorings were also equipped with current meters and/or oxygen sensors. ‘Lab on a chip’ sensors deployed 2 years ago as part of the EPOC project were recovered. CTD stations were conducted throughout the cruise for purposes of providing pre- and post- deployment calibrations for mooring instrumentation. Shipboard underway measurements were systematically logged, processed and calibrated, including: surface meteorology, 5m depth sea temperatures and salinities, water depth, and navigation. Water velocity profiles from 15 m to approximately 800 m depth were obtained using two vessel mounted Acoustic Doppler Current Profilers (one 75 kHz and one 150 kHz).