RRS Discovery D381B

Cruise summary report

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Cruise Info.

Ship name (ship code)

RRS Discovery (74E3)

Cruise identifier

D381B

Cruise period

2012-09-14 — 2012-10-03

Status

Completed

Port of departure

Falmouth, United Kingdom

Port of return

Southampton, United Kingdom

Purpose

Research

Objectives

D381B is a process study cruise to support the NERC's Ocean Surface Boundary layer theme action programme, OSMOSIS (Ocean Surface Mixing, Ocean Sub-mesoscale Interaction Study). The ocean surface boundary layer (OSBL) deepens in response to convective, wind and surface wave forcing, which produce three-dimensional turbulence that entrains denser water, deepening the layer. The OSBL shoals in response to solar heating and to mesoscale and sub-mesoscale motions that adjust lateral buoyancy gradients into vertical stratification. Recent and ongoing work is revolutionising our view of both the deepening and shoaling processes: new processes are coming into focus that are not currently recognised in model parameterisation schemes. In OSMOSIS we have a project which integrates observations, modelling studies and parameterisation development to deliver a step change in modelling of the OSBL. The OSMOSIS overall aim is to develop new, physically based and observationally supported, parameterisations of processes that deepen and shoal the OSBL, and to implement and evaluate these parameterisations in a state-of-the-art global coupled climate model, facilitating improved weather and climate predictions. To support this, D381B has firstly completed mooring and glider deployment work begun during the preceding D381A cruise. Secondly we have carried out several days of targetted turbulence profiling for looking at changes in turbulent energy dissipation resulting from the interation of upper ocean fluid structures such as eddies, sub-mesoscale filaments and Langmuir cells with surface wind and current shear. Finally we have carried out two spatial surveys with the towed SeaSoar vehicle to map and diagnose the mesoscale and sub-mesoscale flows, which, unusually, are the 'large scale' background in which this study sits.

Chief scientist

John T Allen (National Oceanography Centre, Southampton)

Project

Ocean Surface Mixing, Ocean Submesoscale Interaction Study (OSMOSIS), FASTNEt

Cruise report

(9.63 MB)

Ocean/sea areas

General

Celtic Sea

Specific

Porcupine Abyssal Plain site centred around 48° 40’ N, 16° 10’ W, and a square box of side length ~ 50 nautical miles centred approximately around this point.

Track charts

(0.11 MB)

Measurements

Physical oceanography

Surface measurements underway (T,S)

Quantity: activity duration in days = 16
Description: RRS Discovery thermosalinograph data: Conductivity, Temperature, Fluorescence, Optical Transmittance, Wind Velocity, Photosynthetic Available Radiation (PAR), Total Incident Radiation, Air Temperature and Atmospheric Pressure. Underway sampling hourly for Chlorophyll(a), Nutrients and Salinity, 4 hourly for POC, HPLC, BSi, PIC and SEM counts.

Bathythermograph

Quantity: number of profiles = 4
Description: XBT launches: Temperature

CTD stations

Quantity: number of stations = 18
Description: CTD station numbers 381005 - 381022; Conductivity, Temperature, Fluorescence, Optical Transmittance, Oxygen, PAR, Lowered ADCP (LADCP), Optical backscatter. Samples taken typically 4, 6, 8, 12 or 24 depths for Salinity, Oxygen, Nutrients, Chlorophyll(a), POC, HPLC, BSi, PIC, SEM counts.