Dynamics of Southern Ocean Circulation Variability

Supervisors

Nathan Bindoff (UTas), Steve Rintoul (CSIRO)

Project Outline

Background

Recent studies have begun to document the variability of the Southern Ocean and its impacts on regional climate and marine ecosystems For example, the Antarctic Circumpolar Wave is a propagating mode, only identified in the 1990's, that has been linked to changes in Australian climate and Antarctic marine ecosystems. Key Southern Ocean water masses have been shown to be changing in response to climate change. Climate change models predict that the Southern Ocean overturning circulation will slow down as a result of global warming, causing a decrease in the amount of carbon dioxide being absorbed by the ocean and a positive feedback on climate change.

But our understanding of how the circulation of the Southern Ocean varies in time and the impact of Southern Ocean variability on climate and ecosystems remains incomplete, largely due to the lack of observations. Measurements collected during the World Ocean Circulation Experiment in the 1990's started to fill this gap. Combined with data from new observing systems based on autonomous floats, satellites, ships and moorings, we are now in a position to describe and understand the variability of the Southern Ocean for the first time. The integration of the new observations with numerical models provides a means to identify and understand the dynamics driving variability of the Southern Ocean.

Objectives

The aim of the project is to describe and understand the variability of the ocean circulation in the Australian sector of the Southern Ocean. The PhD project will focus on one or more of the following topics:

  • changes in water mass formation and properties
  • climate change detection and attribution
  • variability in upper ocean currents and stratification and their impact on marine ecosystems
  • air-sea-ice interaction

Approach

A variety of observations will be combined to quantify variability in water mass properties (temperature, salinity, oxygen) and circulation features (sea surface height, location and structure of major fronts) in the Australian sector, including variables relevant to biological distributions (eg mixed layer depth, nutrient concentrations). The record of ocean variability will be related to variability in surface forcing (wind, heat, freshwater and sea ice) to identify the dynamical mechanisms driving Southern Ocean variability. The observations will be compared to output from several numerical models: high-resolution ocean hind-casts of ocean conditions in the last decade; experiments designed to test hypotheses of the link between ocean variability and forcing; and output from coupled climate models run with greenhouse forcing scenarios, to relate past change to future change. DynamicWe envision that for this project the emphasis would be on analysis of existing model runs, rather than development of new numerical models.

Data sets

Key data sets will include satellite altimetry, repeat hydrographic sections, autonomous profiling floats, and moorings. Output from a variety of numerical models will be used to test dynamical hypotheses developed through the synthesis of different data sets.

The student will be encouraged to participate in one or more expeditions to the Southern Ocean during the PhD.

Contact

Assoc Prof Nathan Bindoff or tel +61 3 6226 2986