Ernesto Molina

Controls on Southern Ocean Phytoplankton Production - a systems approach.

Supervisors: A/Prof Tom Trull, Dr Andrew Bowie and Dr Mathieu Mongin

Background

For nearly 100 years a central enigma of Southern Ocean marine science has been the observation that phytoplankton biomass levels are relatively low and phytoplankton production does not consume all the available nutrients in these waters (this situation is referred to as HNLC conditions for High-nutrient, Low-Chlorophyll. A series of artificial iron fertilization experiments over the past 5 years has conclusively demonstrated that the low biomass levels result from low availability of iron. Adding iron increases production, and this consumes carbon dioxide, allowing CO2 to be transferred from the atmosphere to the ocean, and thus reducing the impact of this greenhouse gas on climate.

These short-term fertilizations are not able to assess all the ecosystem processes that follow from iron addition, and for this reason it is very useful to explore the role of persistent natural iron inputs in structuring ecosystems and transferring carbon.

The ACE CRC is involved in two studies of naturally elevated biomass regions in the Southern Ocean: 1) the KEOPS program over the Kerguelen Plateau led by French researchers that carried out field observations in 2005, and 2) the SAZ-SENSE project south of Tasmania planned for 2007. The principal aim of this project will be to combine satellite observations of ocean properties with models of primary production and transport to determine the origins of the elevated phytoplankton biomass in these two regions.

This will involve:

• using SeaWiFS and MODIS satellite remote sensing of ocean colour to determine characteristics of the elevated phytoplankton region, including its temporal and spatial dynamics;
• applying and modifying a numerical model of marine microbial ecosystem dynamics to explore the sensitivity of biomass production to iron inputs, light levels, and other controls on production and loss of biomass;
• comparison of the model results to observations of in-situ nutrient and ecosystem characteristics as determined by the KEOPS and SAZ-SENSE field programs; and
• participation in the field programs.

The student will develop skills in:

• retrieval and application of satellite remote sensing data;
• numerical modelling of marine biogeochemistry and microbial ecology; and
• shipboard analysis of biogeochemical characteristics of marine ecosystems.