RRS James Cook Cruise JC064, 10 Sep - 09 Oct 2011. RAPID moorings cruise report

Abstract

This cruise report covers scientific operations conducted during RRS James Cook Cruise JC064. Cruise JC064, departed from Falmouth on Thursday 1st September 2011 arriving Santa Cruz de Tenerife Saturday 10th September to pick up extra members of the scientific party and arriving again in Santa Cruz on the 9th October. The purpose of the cruise was the refurbishment of an array of moorings on the mid-Atlantic Ridge and off the Moroccan Coast at a nominal latitude of 26.5°N. The moorings are part of a purposeful Atlantic wide mooring array for monitoring the Atlantic Meridional Overturning Circulation and Heat Flux. The array is a joint UK/US programme and is known as the RAPID-WATCH/MOCHA array. Information and data from the project can be found on the web site hosted by the National Oceanography Centre Southampton http://www.noc.soton.ac.uk/rapidmoc and also from the British Oceanographic Data Centre http://www.bodc.ac.uk.

The array as deployed in 2011-2012 consists of a total of 17 moorings, 16 landers and a single inverted echo sounder. The moorings are primarily instrumented with self logging instruments measuring conductivity, temperature and pressure. Direct measurements of currents are made in the shallow and deep western boundary currents. The bottom landers are instrumented with bottom pressure recorders (also known as tide gauges), measuring the weight of water above the instrument.

The RAPID naming convention for moorings is Western Boundary (WB), Eastern Boundary (EB) and Mid?Atlantic Ridge (MAR) indicating the general sub?regions of the array. Numbering increments from west to east. An L in the name indicates a bottom lander, M indicates a mini?mooring with only one instrument, H indicates a mooring on the continental slope. During JC064 we recovered: MAR0, MAR1L4, MAR1, MAR2, MAR3, MAR3L4, EB1, EB1L7, EBHi, EBH1, EBH1L7, EBH2, EBH3, EBH4, EBP2, EBH5, EBM5. We did not recover EBM1, EBM4, EBM6, EBH1 and MAR3. We deployed: MAR0, MAR1L7, MAR1, MAR2, MAR3, MAR3L6, EB1, EB1L7, EBHi, EBH1, EBH1L8, EBH2, EBH3, EBH4, EBP2, EBH5. A sediment trap mooring NOGST was also recovered and redeployed for the Ocean Biogeochemistry and Ecosystems Group at the NOCS.

CTD stations were conducted at convenient times throughout the cruise for purposes of providing pre and post deployment calibrations for mooring instrumentation and for testing mooring releases prior to deployment.

Shipboard underway measurements were systematically logged, processed and calibrated, including: waves (spectra of energy and significant wave height), surface meteorology (air pressure, temperature, wind speed and direction and radiation (total incident and photosynthetically active), 6m?depth sea temperatures and salinities, water depth, navigation (differential GPS measurements feeding two independent and different receivers, heading, pitch and roll, gyro heading and ships speed relative to the water using an electromagnetic log). Water velocity profiles from 15m to approximately 800m/300m depth were obtained using a ship mounted 75/150 kHz acoustic Doppler current profiler. Seawater samples from CTD stations and of the sea-surface were obtained for calibration and analysed on a salinometer referencing these samples against standard sea water. For velocity data (wind and currents) measured relative to the ship considerable effort was made to obtain the best possible earth referenced velocities.

Seven APEX argo floats supplied by the Met Office were deployed at preassigned locations, filling gaps in the network.

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