Title: Nutrient controls, distribution and productivity of phytoplankton in the Tasman Sea.
Supervisors: Dr. Martina A. Doblin and Dr. Christel Hassler (UTS)
Phytoplankton is responsible for approximately 40% of global carbon drawdown. They are the base of the marine food web and are integral to global nutrient and carbon cycling. In Australian waters phytoplankton is regulated by the availability of light, temperature and nutrients. Specifically in the northern Tasman Sea, which is a rapidly warming region of the ocean, phytoplankton growth is typically nutrient-limited. These waters are dominated by Picoplankton (0.2-2µm) and heterotrophic bacteria which are able to utilise oligotrophic waters relatively efficiently. To overcome this limitation in nutrient availability some phytoplankton fix nitrogen from the atmosphere which is an energy intensive process requiring other nutrients such as iron.
The southern sector of the Tasman Sea is characterised by nutrient replete waters and larger sized phytoplankton (2-10µm) as a result. It is known that the Southern Ocean is a highly productive area for phytoplankton and it is therefore important to have an understanding of how changes in temperature and nutrient loading can affect these phytoplankton communities.
1) Determine the phytoplankton species composition at three different stations representing oligotrophic tropical water, intermediate water and nutrient-rich subantarctic water.
2) Examine the links between phytoplankton nutrient status and photo-physiological responses.
3) Identify changes in phytoplankton productivity along a latitudinal transect from north to south.
Phytoplankton sampling and experimentation was conducted on board the RV Southern Surveyor during a cruise from 21 January to 15 February, 2010. Three different water types were sampled across a latitudinal gradient oligotrophic tropical water, intermediate water and nutrient replete sub-Antarctic water. A CTD (Conductivity, temperature & depth) rosette which had 20 niskin bottles attached to it was deployed from the RV Southern Surveyor to facilitate the sampling of sea water at different depths. Parameters such as productivity, fluorescence and temperature were collected alongside size fractionated and lugols fixed samples.