BROKE West Survey, Marine Science Cruise AU0603 - Oceanographic Field Measurements and Analysis

Brief description

Oceanographic measurements around the 'BROKE-West' survey area along the Antarctic continental margin between 30 degrees and 80 degrees south were conducted aboard Aurora Australis cruise au0603 (voyage 3 2005/2006, 2nd January to 12th March 2006). A total of 120 CTD vertical profile stations were taken, most to within 15 m of the bottom. Over 2500 Niskin bottle water samples were collected for the measurement of salinity, dissolved oxygen, nutrients (phosphate, nitrate+nitrite, silicate and ammonia), 18O, dissolved inorganic carbon, alkalinity, particulate organic carbon/nitrogen/silicate, dimethyl sulphide, and biological parameters, using a 24 bottle rosette sampler. Full depth current profiles were collected by an LADCP attached to the CTD package, while near surface current profile data were collected by a ship mounted ADCP. Data from the array of ship's underway sensors are included in the data set.

This report describes the processing/calibration of the CTD and ADCP data, and details the data quality. An offset correction is derived for the underway sea surface temperature and salinity data, by comparison with near surface CTD data. LADCP data are not discussed in this report. Note that the data processor was not a cruise participant, thus this report does not describe all details of the shipboard field data collection or the problems encountered. CTD station positions are shown in Figures 1a and b, while CTD station information is summarised in Table 1. Niskin bottle sampling at each station is summarised in Table 2. (see word document detailed below for figures and tables)

Further information is available in a word document available as part of the download.

This work was completed as part of ASAC projects 2655 and 2679 (ASAC_2655, ASAC_2679).

Lineage

Progress Code: completed

Statement: SeaBird SBE9plus CTD serial 704, with dual temperature and conductivity sensors and a single SBE43 dissolved oxygen sensor (on the primary sensor pump line), was used for the entire cruise, mounted on a SeaBird 24 bottle rosette frame, together with a SBE32 24 position pylon and 22 x 10 litre General Oceanics Niskin bottles. The following additional sensors were mounted:

* Benthos model 2110 altimeter
* Tritech 200 kHz and 500 kHz altimeters
* Wetlabs fluorometer serial 296
* photosynthetically active radiation (i.e. PAR) sensor
* Wetlabs C-star transmissometer serial 899DR
* Sontek lowered ADCP (i.e. LADCP) with upward and downward looking transducer sets

CTD data were transmitted up a 6 mm seacable to a SBE11plusV2 deck unit, at a rate of 24 Hz, and data were logged simultaneously on 2 PC's using SeaBird data acquisition software 'Seasave'. The LADCP was powered by a separate battery pack, and data were logged internally and downloaded after each CTD cast. Note that physical mounting of the upward looking LADCP transducer set requires removal of 2 Niskin bottles, thus only 22 Niskins were fitted for the cruise.

The CTD deployment method was as follows:

* CTD initially deployed down to ~20 m
* after confirmation of pump operation, CTD returned up to just below the surface (depth dependent on sea state)
* after returning to just below the surface, downcast proper commenced.

For most casts, the package was stopped for 5 minutes on the upcast at ~50 m above the bottom, for logging of LADCP bottom track data.

Pre cruise temperature, conductivity and pressure calibrations were performed by the CSIRO Division of Marine and Atmospheric Research calibration facility (Table 3) (July to August 2005). Manufacturer supplied calibrations were used for the dissolved oxygen, fluorometer, transmissometer and altimeters. PAR data are uncalibrated. Final conductivity and dissolved oxygen calibrations derived from in situ Niskin bottle samples are listed later in the report.