Position analysis: Antarctic sea ice and climate change 2014

The annual expansion and contraction of sea ice in the Antarctic represents one of the biggest natural changes on Earth. At its maximum annual extent in September/October sea ice cover extends about 19 million square kilometres of the ocean around Antarctica – one and half times the size of the continent itself. In the summer sea ice shrinks to around 3 million square kilometres.

Antarctic sea ice plays a major role in the global climate system and in the ecology of the Southern Ocean. The sea ice region is the source of Antarctic Bottom Water, a major driver of global ocean overturning circulation. Sea ice is important in reflecting solar energy back into space. It is a habitat and a source of primary production for Southern Ocean ecosystems.

Sea ice cover in the Antarctic is changing. In the west Antarctic Peninsula region, sea ice extent has dramatically reduced, and the length of the sea ice ‘season’ has also shortened. In the Ross Sea region of the Antarctic, however, the maximum annual extent of sea ice cover has increased and its season extended. Overall, the maximum annual extent of Antarctic sea ice has increased by around 1.5% per decade since 1979 (or by around 285,000 square kilometres). This compares to a loss of 1.8 million square kilometres of sea ice maximum annual extent in the Arctic.

One important aspect of Antarctic sea ice that we know very little about is change to its volume. While satellites can measure the aerial extent of sea ice, reliable methods to remotely measure sea-ice thickness are only just emerging. In contrast, data from submarines in the Arctic have allowed detailed monitoring of regional changes to Arctic sea-ice thickness over a number of decades.

What is happening in the physical, chemical and biological systems beneath Antarctic sea ice is poorly understood. Because of the critical role of sea ice, it is vital that we develop a better understanding of the future trends in sea ice extent and volume, and consequences for Antarctic and Southern ocean ecosystems.

Australia is well placed to take a lead role in these studies - especially in the East Antarctic. Australia has a mature Antarctic research program that has demonstrated that it can collaborate with other nations, and across scientific disciplines, to do the complex science that is required to understand these important issues. Having the logistic and infrastructure capabilities will be vital to ensuring that this important region of the planet is understood.