Australian scientists find new evidence of Antarctic sea ice decline

A view of the outdoor field camp on ice at Law Dome
Law Dome field camp (Photo: Grant Dixon)

14 November 2003

Glaciologists from the Australian Government's Antarctic Division (AAD) have found evidence of a decline in the extent of Antarctic ice.

In a paper published in the latest edition of the prestigious journal, Science, out today, Dr Mark Curran and colleagues find evidence that the decline of sea ice around Antarctica is more pronounced than previously believed and has provided the first long-term record of sustained decline.

Dr Curran said that examination of chemical signals in an ice core taken from Law Dome near Australia's Casey station in Antarctica indicated a diminution in the sea ice of around 20 per cent in the past 50 years.

"At first glance this could appear to be at odds with recent opinion that sea ice is not decreasing and may, in fact, be increasing," Dr Curran said.

"However, what we need to take into account is that until now records have relied, to a large degree, on satellite observations since the 1970s and our work illustrates that 30 years is a very short time over which to draw any conclusions.

"This latest research, from the top 150 metres of the Law Dome ice core extends our knowledge back to 1840 and explains why satellite trends are confusing. Detection of long-term change is masked by large fluctuations from decade to decade and it is these decadal fluctuations that have produced apparent short-term increases in the satellite data," he said.

The ice core was calibrated by comparing the recent section that overlaps the period of satellite coverage – 1974 to 1995.

Dr Curran said that in this new study scientists had measured levels of Methane Sulphonic Acid (MSA) – an atmospheric aerosol produced as a result of phytoplankton activity at the surface of ocean waters. Phytoplankton are small single-cell ocean plants that are a major food source for species such as krill and other grazers. In the Southern Ocean, phytoplankton activity is closely linked to sea ice distribution and so a relationship between MSA concentrations in the atmosphere and sea ice was envisaged.

"In the oceans around Antarctica, sea ice forms and decays each year. It plays an important function in climate control, ocean circulation, heat exchange and ecosystem support. Very little is known of its extent prior to 1974.

"However, what we can say with data obtained from the ice core is that between 1841 and 1950 there was very little change but there is a marked decline in sea ice distribution since 1950 of around 20 per cent," Dr Curran said.

Dr Curran said that whether the decline was a result of climate change or part of a natural cycle would only be determined over time as more pieces of the puzzle were assembled and compared.

These findings are remarkably similar to those of former AAD scientist Professor William de la Mare. His novel research, published in 1997, into whaling records contended that the Antarctic summer sea ice edge had moved southwards by 2.8 degrees of latitude between the 1950s and 1970s and represented a decline in area covered by sea ice of around 25 per cent.

It had become a well-established practice by whalers to rest their ships up against the edge of the sea ice while taking their catch and to follow the ice south as it retreated.

From 1931 until the end of commercial whaling in 1987 records were kept for every whale caught and Professor de la Mare believed it was a useful data resource that should not be overlooked.

This latest research by Dr Curran and colleagues produces evidence that confirms Professor de la Mare's earlier work and indicates Australia's significant contribution to this important research.