RRS Discovery D224A
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS Discovery (74E3) |
| Cruise identifier | D224A |
| Cruise period | 1996-11-27 — 1996-12-29 |
| Status | Completed |
| Port of departure | Southampton, United Kingdom |
| Port of return | Cartagena, Spain |
| Purpose | Research |
| Objectives | Experimental field observations and Modelling of Eddy scale Geostrophic and Ageostrophic motion for the EU MAST 3 project (OMEGA). First part of two leg cruise
1) To determine the 3 dimensional ageostropic circulation at mesoscale fronts and eddies and quantitatively estimate the vertical velocity 2) To evaluate the impact of the ageostrophic vertical motion on the biogeochemical properties in the upper 400 m 3) To provide the scientific community with a standardised tool for the computation of vertical motions from routine CTD and ADCP data. |
| Chief scientist | John T Allen (Southampton Oceanography Centre), Trevor H Guymer (Southampton Oceanography Centre) |
| Project | OMEGA |
| Cruise report |  (1.55 MB) |
| Ocean/sea areas | |
| General | Mediterranean Sea |
| Specific | Alboran Sea, western Mediterranean |
| Track charts | (0.18 MB) (0.19 MB) (0.19 MB) (0.19 MB) (0.19 MB) (0.18 MB) |
| Measurements | |
| Physical oceanography | |
| Surface measurements underway (T,S) | Description: Sea surface radiometers were taken to provide bulk temperatures for evaluating the air sea fluxes of heat and water in the area of the Almeria-Oran front. It increased the data set available for evaluating and modeling the sea surface skin effect and provided measurements of the skin temperature of the ocean for validation of satellite SST data. |
| CTD stations | Quantity: number of stations = 15 Description: CTD stations were accompanied by detailed measurements of ocean properties at strategic locations along and across the front. 12 bottles, a fluorometer, a transmissometer, an altimeter and an ADCP were also mounted on the CTD frame. |
| Subsurface temperature and salinity measurements | Description: Salinity bottle sample analysis and thermosalinograph data. Salinity samples were taken from each CTD Niskin. Underway surface conductivity and temperature measurements from the thermosalinograph were continuously logged using the RVS surflog system. |
| Optics (eg underwater light levels) | Description: Optically Active Parameters (OAP)/Gelbstoff. All optical measurements were accompanied by water quality measurements to allow calibration of the SUMOSS and Secchi discs. Parameters measured were suspended particulate matter, spectral absorption coefficient, phytoplankton counts. Studies of the distribution and variability of dissolved organic matter in the area under investigation were carried out. |
| Optics (eg underwater light levels) | Quantity: number of deployments = 6 Description: SUMOSS to measure apparent and inherent optical properties at high spectral resolution. Secchi disc observations were also made. 3 coloured discs were made during the period when SUMOSS was under repair. |
| Current profiler (eg ADCP) | Description: Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP). The ADCP deck unit was set up to record data for 100 bins, each 4 m thick, with an offset of 8 m and a 2 minute ensemble period. The bottom track calibration was done on the Celtic shelf at a ship speed of 8 knots. A Lowered ACDP was used on most CTD stations, especially the deeper ones which extended beyond the range of the shipboard ADCP. ACDP Backscatter - information was used to determine the density of particles in the water column including some of the larger zooplankton species. |
| Instrumented wave measurements | Description: Shipborne Wave Recorder (SBWR) information was obtained used to interpret wind stress data and verify a new version of the Shipborne Wave Recorder and UDP data transfer tool. |
| Chemical oceanography | |
| Phosphate | Description: 2 Chemlab autoanalysers were used for the analysis of nutrient data. The discrete autoanalyser was used for the analysis of hourly surface samples and CTD samples. The continuous autoanalyser was connected to the nontoxic seawater supply. Duplicate hourly samples were also collected throughout the cruise, duplicate nutrient samples were also collected from 14 CTD stations. |
| Nitrate | Description: 2 Chemlab autoanalysers were used for the analysis of nutrient data. The discrete autoanalyser was used for the analysis of hourly surface samples and CTD samples. The continuous autoanalyser was connected to the nontoxic seawater supply. Duplicate hourly samples were also collected throughout the cruise, duplicate nutrient samples were also collected from 14 CTD stations. |
| Silicate | Description: 2 Chemlab autoanalysers were used for the analysis of nutrient data. The discrete autoanalyser was used for the analysis of hourly surface samples and CTD samples. The continuous autoanalyser was connected to the nontoxic seawater supply. Duplicate hourly samples were also collected throughout the cruise, duplicate nutrient samples were also collected from 14 CTD stations |
| Other chemical oceanographic measurements | Quantity: number of surveys = 6 Description: The SeaSoar fitted with a CTD, a fluorometer, a light sensor and a back scatter sensor was deployed. Towing the undulating CTD vehicle, SeaSoar, 2 large scale and 3 fine scale SeaSoar surveys were made of the Almeria-Oran front region of the Western Mediterranean. A brief SeaSoar survey was made of the head of the Algerian Current. A Sea-Tech optical backscatter probe was fitted to SeaSoar during both of the Omega cruises |
| Biology and fisheries | |
| Phytoplankton pigs (eg chlorophyll, fluorescence) | Quantity: number of stations = 15 Description: Water samples were analysed for their chlorophyll and phaeopigment content to calibrate the CTD fluorometer, the TSG fluorometer and subsequently the SEaSoar gluorometer. Analyses were used to obtain a rapid view of biological properties of the water, to allow a comparison with physical data obtained continuously at real time and to calibrate data from SUMOSS and satellite images. CTD chlorophyll samples were taken at 5, 50, 100 and 200 m depth at every CTD station, with a further sample taken at the chlorophyll maximum. Underway samples were taken hourly when SeaSoar was deployed and were drawn from the non-toxic supply in the hanger which also feeds the TSG fluorometer. |
| Seston | Description: Optical Plankton Counter (OPC). The instrument used on SeaSoar was fitted with an acrylic flow insert to reduce the tunnel cross section for towed use and was mounted beneath the SeaSoar body in place of the usual torpedo shaped balance weight. |
| Seston | Quantity: number of deployments = 8 Description: Longhurst Hardy Plankton Recorder tows were made to look at the change in planktonic species composition across frontal zones. Run in internal logging mode. |
| Seston | Description: Flow cytometry was used to determine the functional composition (cell density) and size structure of the phytoplanktonic community in the size range of 0.5 to 20 micrometres in near real time to match the surface spatial scales of physical data obtained by SeaSoar, SUMOSS, CTD satellite images etc. Surface samples were taken hourly from the non-toxic continuous flow during SeaSoar surveys, SUMOSS, and LHPR deployments. Several additional samples were taken when requested. Vertical profiles were obtained by sampling the CTD Rosette bottles. The samples were taken from the bottles triggered at different depths |
| Meteorology | |
| Upper air observations | Quantity: number of deployments = 75 Description: Radiosonde launches made throughout the cruise, between 2 and 4 times daily, providing vertical profiles of temperature, humidity, and wind speed in the troposphere. It also enabled an analysis to be made of changes in the stability of the boundary layer across the Almeria-Oran front. RS80-15G and the standard PTU sonde RS80-15 were released. |
