Ice, Ocean, Atmosphere and Climate - program overview

The tongue of this glacier extends in to a frozen lake. Photo: Ian Allison

The overarching goal of this priority area program is to better understand and quantify the role of Antarctica and the high-latitude Southern Ocean and atmosphere in the global climate system.

Antarctica and its surrounding ocean are dominated and shaped by the presence of snow and ice which, while themselves controlled by the climatic regime and very sensitive to climate change, also influence and provide major feedbacks to the global climate system.

Many globally significant processes are driven by the unique climate and geography of the Antarctic region. These include the uptake of carbon dioxide by the Southern Ocean; the overturning circulation of the deep ocean; the balance between water storage and discharge in the main continental ice-sheet; changes in surface energy, mass and momentum exchange by ice masses; and energy transfer between all levels of the atmosphere to space. Understanding these processes is vital for understanding and predicting climate and environmental changes and their impacts. These impacts include future greenhouse gas levels, sea-level rise, the variability and rate of change of climate, and changes in atmospheric composition. The latter includes the stratospheric 'ozone hole', which affects life in Southern Hemisphere nations.

To better predict future climate we need better earth system models that describe the earth-ocean-atmosphere-ice interactions. This requires us to understand the individual components as well as their interactions, determine the parameters that quantify the processes described by the models, and obtain improved data sets to support these activities. To achieve this, the Ice, Ocean, Atmosphere and Climate program aims to answer the following questions.

What is the role of the Antarctic cryosphere in the global climate system and sea level change?

Heard Island glaciers such as Brown Glacier, have retreated significantly over the last 50 years. Photo: Chris Stevenson

During winter the sea ice extent around Antarctica's coastline is approximately 19 million square kilometres - an area nearly three times the size of Australia. Sea ice has a significant influence on the mean state and variability of regional and global climates. The extent to which a cover of sea ice modifies ocean-atmosphere interaction is determined primarily by the thickness and concentration of the ice and by the thickness and density of its snow cover.

Salt rejection during the autumn ice formation, followed by ice advection and subsequent summer melt further north, results in a net freshwater flux and change in ocean buoyancy. The ice thickness, ice drift and snow cover on the ice are themselves determined by ocean-atmosphere interactions.

Deep and bottom water formation south of the Antarctic Circumpolar Current occurs mostly through dense water formation, by cooling and brine release, on the Antarctic continental shelves. Sea ice formation counteracts freshwater gain by precipitation, minus evaporation and melting of ice shelves and icebergs.

Research is required to better understand ice shelf and water mass modification processes. Sea ice and the hydrological processes involving glacial ice, crucially affect the thermohaline circulation (THC), which has been implicated in both abrupt and long-term climate change. But it is not clear if changes in the THC drive significant changes in climate, or if they are a consequence of climate change. It is a serious concern that changes in the cryosphere could lead to abrupt changes in global climate; the stability of the climate in response to such forcing and the likelihood of abrupt change is not well known.

Studies of the integrated role of the cryosphere in the global climate system, and the impact of cryospheric changes on both atmospheric and oceanic circulation, requires appropriate treatment of many different cryospheric processes in coupled climate models.

What are the Southern Ocean processes responsible for climate variability and predictability on seasonal, inter-annual, decadal and longer timescales, and how do these influence sea-level? What is the magnitude and current uptake of atmospheric carbon dioxide by the Southern Ocean, and what processes control this?

Improved understanding of Southern Ocean processes is essential if key global questions are to be addressed. Processes and issues of relevance include variability of the oceanic overturning circulation, sub-tropical cells and low-frequency variability of ENSO, ocean uptake of carbon, climate change detection and attribution, regional climate variability (including the Australian region), basin-scale heat and freshwater budgets, global temperature response to greenhouse forcing, centennial variability, and sea-level rise.

Southern Ocean research to be undertaken is based on sustained observations and modelling efforts in line with the four areas of importance to the Southern Ocean and climate: the 'shallow' overturning cell, the 'deep' overturning cell, inter-basin exchange, and teleconnections and low-frequency variability.

The oceans south of 40°S contain roughly 40% of the global oceanic inventory of CO₂ and a small change in this can have a significant effect on atmospheric CO₂. Research will address the role of the Southern Ocean in the global carbon cycle and also other biogeochemical cycles.

What changes are occurring in the climate of Antarctica and the Southern Ocean, and what are the links between these changes and the global climate system?

Wind erosion has revealed ice and sediment layers built up overs hundreds of years, near Mawson. Photo: Peter Harris

The instrumental record of climate change is limited, especially in the high latitude Southern Hemisphere. Better data is needed for model validation, and in studies for detection and attribution of climate change. Palaeoclimate records from Antarctic ice cores, Southern Ocean sedimentary records, and other geomorphological sources, provide such data for the whole region, on timescales ranging from sub-annual to millions of years.

Palaeoclimate records from various locations in Antarctica and the Southern Ocean will be used to improve our understanding of past climate change and to generate data for predictive models of future change. That the planet's climate is in a state of constant change from natural phenomena is no longer in doubt. What is required is an accurate understanding of the relative importance of various forcings and the mechanisms, the speed of responses, and the patterns of natural variability. This work will provide for improved model validation and boundary conditions for simulations of past changes. Ice core records of accumulation variability in Antarctica will contribute to studies of mass-balance and associated sea-level influences.

What role do the dynamics and composition of the whole atmosphere play in climate processes and how are these changing?

The MST radar at Davis measures wind speed and direction over a wide range of heights in the middle atmosphere. Photo: Damian Murphy

Over 70% of Earth's equator-to-pole energy is transported by atmospheric processes. The atmosphere is a region where clear human influence has been detected, for example, in increased greenhouse gas concentrations, and in the 'ozone hole'. It is often not clear how anthropogenic change affects climate and how it influences atmospheric chemistry and energy transport. Processes in the lower atmosphere interact with oceanic and cryospheric processes. Higher up, links between the troposphere weather and stratospheric processes are becoming apparent. The strength and duration of the so-called polar vortex over Antarctica in winter have a significant impact on regional and Southern Hemisphere climate. Research into these matters will advance our understanding of the Antarctic's role in climate.

Mesospheric processes are also showing important links to the lower atmosphere, with gravity waves and circulation that feeds back to the stratosphere. Research into these and other poorly understood processes will assist the incorporation of the middle and upper atmosphere, including links to geospace, into future climate models.