RAPID 26N Report for RRS Discovery Research Expedition DY204 2nd - 10th February 2026. B. I. Moat, T. Petit and Y. L. Firing. 2026

The purpose of RRS Discovery research expedition DY204 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 2nd February 2026 and ended on 10th February 2026 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-MOCHAWBTS array is a joint UK-US programme.

During DY204 moorings were serviced at sites: EBH3, EBH3L, EBH2, EBH1, EBH1L. 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.

CTD stations were conducted throughout the cruise for purposes of providing pre- and postdeployment 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 800m depth were obtained using two vessel mounted Acoustic Doppler Current Profilers (one 75 kHz and one 150 kHz).