RRS Discovery Cruise DY039, 17 Oct - 01 Dec 2015, Southampton, UK to Nassau, Bahamas. RAPID moorings cruise report

Abstract

This cruise report covers scientific operations conducted during RRS Discovery Cruise DY039. The purpose of the cruise was the refurbishment of an array of moorings spanning the latitude of 26.5°N from the Bahamas to the Canary Islands. Cruise DY039 departed from Southampton, UK on Saturday 17 October 2015, calling at Tenerife, Spain and Nassau, Bahamas before ending in Nassau, Bahamas on 21 November 2015.

The moorings are part of a purposeful Atlantic wide mooring array for monitoring the Atlantic Meridional Overturning Circulation and the associated heat transport. The array is a joint UK- US programme and is known as the RAPID-MOCHA array.

During DY039 moorings were serviced at sites: EBH4, EBH4L, EBH3, EBH2, EBH1, EBH1L, EBHi, EB1, EB1L, MAR3, MAR3L, MAR2, MAR1, MAR1L, MAR0, WB6, WB4, WB4L, WBH2, WB2, WB2L, WB1, WBADCP and WBAL. Sites with suffix ‘L’ denote landers fitted with bottom pressure recorders.

RAPID-AMOC continues the measurements at 26°N started with the RAPID and RAPID-WATCH programmes and through the ABC Fluxes project extends the measurements to include biological and chemical measurements in order to determine AMOC links to climate and the ocean carbon sink on interannual-to-decadal time scales. This is the first deployment of the ABC Fluxes biogeochemical samplers and sensors to the array (aside from initial oxygen sensors that were deployed in 2014).

The ABC Fluxes sensors include pCO2 sensors, pH sensors, additional oxygen sensors and autonomous water samplers to collect samples for nutrient and carbonate chemistry analysis following mooring recovery.

Additionally the RAPID telemetry MkIII system was deployed for the first time on the array at EBHi with 6 data pods set to release over the 18-month deployment period. 24 temperature sensors and 2 75kHz ADCPs were also added to mooring WB1 for the MerMEED project.

Mooring EB1L was not able to be recovered but a replacement was deployed. A sediment trap mooring NOGST was also recovered and redeployed for the Ocean Biogeochemistry and Ecosystems Group at the NOCS.

CTD stations were conducted throughout the cruise for purposes of providing pre- and post- deployment calibrations for mooring instrumentation (including oxygen and carbonate chemistry sampling) and for testing mooring releases prior to deployment.

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 the two vessel mounted Acoustic Doppler Current Profilers (one 75 kHz and one 150 kHz).

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