The Origins of Interannual Variation in Southern Ocean Export Production

Supervisors

Tom Trull (UTas), Richard Matear (CSIRO)

(PhD Only)

Project Outline

Since 1997, the SAZ Project, organized by the ACE CRC, CSIRO Marine Research and other agencies, has maintained deep ocean automated sediment trap moorings in the Sub-Antarctic, Polar Frontal, and Antarctic Zones of the Southern Ocean. These records of sinking particle flux show large variations in both seasonality and integrated annual amplitude. Determining the cause of this variability is essential to the application of the flux results to models of carbon redistribution within the sea by biological processes. This redistribution affects the magnitude of atmospheric carbon dioxide levels and the coupling of pelagic and benthic ecosystems.

The principal aim of this project will be to combine satellite observations of ocean properties with models of particle production and transport to determine the origins of this variability.

This will involve:

a) evaluating the "primary" production of organic carbon by phytoplankton synthesis using SeaWiFS and MODIS ocean colour estimates of phytoplankton characteristics

b) estimating the fraction of this "primary" production which is "exported" to the deep sea, based on both temperature parameterizations (driven by AVHRR SST estimates) and food-web models

c) developing a model of particle aggregation and sinking

d) applying satellite altimetry to estimate the current driven redistribution of sinking particles as they leave the surface and their subsequent collection by the sediment traps.

The simulated particle production and regional sources will then be compared with the measured chemical and biological characteristics of the collected particles to determine if they represent significantly different origins among the main planktonic functional groups, and to refine the particle production and transport models. The project also has scope to undertake laboratory and field studies to determine particle sinking rates - considered to be a key controlling variable on the fraction of primary production which reaches the deep sea. In particular, cruises in the central and North Pacific in June 2004 and June 2005 as part of the US NSF funded VERTIGO (vertical flux in the global ocean) program.

The student will develop skills in:

a) retrieval and application of satellite remote sensing data

b) the quantification of marine particle process such as aggregation, sinking, and transport.

These skills will be useful to students interested in a range of possible career directions, including pelagic marine ecosystems, fate of marine contaminants, and the impacts of climate change and variability on global biogeochemical cycles.

Contact

A/Prof Tom Trull or tel +61 3 6226 2988