Antarctic Voyage: The oceanography team

By Guest Author 05/02/2013

Dr Helen Bostock, marine geologist at NIWA, writes

Date: 4/2/2013
Position: 45.66345˚S, 171.2626˚E
Weather: Cloudy and raining
Sea state: Calm

While we are transiting to our first station over the next few days, I will introduce the members of the science teams and the main instruments they will be using during the voyage.

CTD hanging off the side of the Tangaroa (from TAN0803 voyage, credit: NIWA)

There are scientists from three different disciplines on board: oceanographers, chemists and geologists (the latter are also doing a little biology).

Some other statistics: although we are from institutions in 3 different countries, there are actually 8 different nationalities on board – New Zealanders, Australians, English, Americans, Canadians, French, Spanish, and the ice pilot is Danish. Interestingly, there are more female scientists (14) than male (8) scientists participating on this voyage!

The oceanography team is made up of Mike Williams (the voyage leader), Fiona Elliot, Matt Walkington (NIWA), Bea Molino, Mark Rosenberg (ACE CRC), Emmanuelle Sultan, Marie Noelle Houssais, Hervé Le Goff (L’ocean) and three PhD students – Aitana Forcen (NIWA), Eva Cougnon (ACE CRC), and Antoine Martin (L’ocean).

Together this team is responsible for running the CTD (conductivity, temperature, depth profiler – pronounced seeteedee), which measures the salinity, temperature, pressure, and oxygen in the water as we lower it the sea floor. The team also collect water samples at different depths on the way back up to the surface, to calibrate the sensors on the CTD, and for the chemists to analyse. Similar sensors on the ship’s ‘underway’ system also collect continuous surface water data along the ship’s track.

Aitana Forcen sampling the CTD during TAN1106 voyage (credit: Bruce Hayward, Geomarine Research)

Attached to the CTD frame is an ADCP (Acoustic Doppler Current Profiler) which measures flow speeds at different depths in order to get an idea of the currents. There is another ADCP attached to the bottom of the ship that constantly measures the currents in the upper few hundred metres. The ADCP works by sending out pulses of sound that bounce off objects in the water; then they pick up the change in frequency of the reflected sound pulse to determine the speed of the objects in the water, which we take to be is the same as the water speed.

The oceanography team is also responsible for the moorings. These are a series of instruments measuring temperature, salinity, and currents, attached to a long cable. The cable is held down by a weight which sits on the seafloor, and then held upright in the water with a series of floats. While a CTD takes a snapshot of what is going on in the water column, moorings are usually deployed for a few months or a couple of years to monitor seasonal or interannual changes.

Mooring hanging above the water (credit: Mark Rosenberg, ACE CRC)

One of the main objectives of this voyage is to retrieve some moorings that the Australians and French teams put out into the ocean over a year ago to measure changes in the water column on the shelf near the Mertz Glacier. As the moorings sit below the surface of the ocean, the instruments should have measured the water column even in the middle of winter when the sea ice freezes over this region and there is no way a ship can get in.

Together the physical and chemical properties of the water can be used to trace different water masses in the ocean. When the data is compared to previous voyages to this region, it also tells us how the water mass properties are changing over time.