Southern Ocean

The Southern Ocean is the stormiest place on the earth. The uninterrupted ocean circling Antarctica creates a freeway for winds and waves to strengthen like nowhere else on earth. It is sheathed in clouds which hide a dynamic ocean with rich ecosystems. This significant region of the earth influences the atmospheric circulation and composition of the entire Southern Hemisphere and beyond.

The atmosphere of the Southern Ocean region is amongst the cleanest in the world. With less than 5% of the world population living south of 30oS, anthropogenic influence is minimal compared to the highly polluted Northern Hemisphere. This makes the region a unique testbed for understanding natural atmospheric processes without being convoluted with the complex processes associated with the strong anthropogenic signals.

Due to the unique pristine environmental conditions in the Southern Ocean, atmospheric composition and chemistry behaves distinctly different from elsewhere. Aerosols, particles suspended in the atmosphere, are in much lower concentrations than other parts of the globe. The subset of aerosols that can act as seeds for cloud droplet formation, Cloud Condensation Nuclei (CCN) and cloud ice formation, Ice Nuclei (IN), are orders of magnitude lower. Gas phase chemistry is limited primarily to natural emissions from things such as phytoplankton, penguin rookeries and volcanoes. Clouds in the region occur at lower heights and their properties such as lifetime and whether they are in a liquid or ice phase differ notably from their northern hemisphere equivalents.

The distinctive oceanic circulation within this region means that, in some areas, deep carbon-rich water is brought to the surface, while in other surface water is drawn down. As such, the Southern Ocean can act both to pump CO2 into the atmosphere and in other regions to absorb it from the air above. While the Southern Ocean is currently a net sink of CO2, the balance between uptake and release processes is precarious. Considering that the Southern Ocean is currently one of the largest oceanic sinks of CO2 (about 40% of the global ocean uptake of CO2), measuring and understanding this variability is vital. Doing so will provide essential insight into the global carbon budget and thus the likely trajectories of climate change under a range of emissions scenarios.

The wild conditions and remoteness of the Southern Ocean make measurements in this region difficult, especially in winter, and consequently, our understanding of the physical and chemical processes which occur here is poor. This means that satellite records, and climate and earth system models that are regularly validated further north, contain high uncertainties in the Southern Hemisphere.

More studies, both observational and modelling based, are required to help understand this region and the impact is has on the rest of the world. We work with the Bureau of Meteorology, the Australian Antarctic Division, and CSIRO’s Marine National Facility to operate long-term observations at the Cape Grim Baseline Air Pollution Station, on a number of Antarctic and sub-Antarctic stations, and aboard the RV Investigator, as well as undertake a variety of intensive field campaigns, to help to understand this unique environment. We then work with our in-house modelling team, as well as international collaborators, to utilise these unique measurements to improve our earth system and climate models.

Atmospheric measurements in the Antarctic Marginal Ice Zone of the Southern Ocean while aboard the Aurora Australis. Photo: Ruhi Humphries