Climate variability in Eastern Wilkes Land: Australian ITASE ice core drilling, 2003-04

This past season a six person ice-coring team was deployed for two weeks at a remote location in Wilkes Land some 750 km east of Casey. The aim of this project was to recover ice cores to provide records of past climate in this region. This was a cooperative project, between the Environmental Geoscience Group at the University of Newcastle and the AAD Glaciology Program, and called for a complex logistical effort using two Twin Otter aircraft to ferry personnel and equipment the 2.5 hour trip from Casey, via a fuel depot, to the field camp.

At the conclusion of the season, researchers had retrieved a 147 m deep core from the main field site and collected numerous shallow cores and undertaken radar studies to explore the spatial variation within the snow pack.

The reason for such a major undertaking lies in the rich record of climate information that ice-cores can provide, extending back far beyond the instrumental record (for example see 'Ice core evidence for 20% decline in Antarctic sea ice extent since the 1950s' on page 22).

Antarctica and high southern latitudes play an important role in global climate, and climate records from this region are a key to better understanding climate change. Unfortunately, historical records of Antarctic climate are short, mostly dating from the International Geophysical Year in 1957, or even later, and the spread of sites is sparse.

The Wilkes Land project is part of the multi-national ITASE Program (International TransAntarctic Scientific Expedition). ITASE was formulated in 1990, with strong Australian input, in response to a need for more records of climate variability across Antarctica. The focus for ITASE is on climate and environmental records of the past 200 years – a period covering the time of increasing human influence on the global atmosphere. Most ITASE climate records are derived from ice cores, although other measurements, such as the temperatures of boreholes and subsurface radar profiles are also used to provide climate information.

The ITASE program currently involves nineteen nations and is sponsored by the International Geosphere-Biosphere Program (IGBP) and Scientific Committee on Antarctic Research (SCAR).

So far, internationally more than ten long traverses have been undertaken and numerous ice cores have been recovered from most areas of the continent. Australian contributions have been made in the Lambert Glacier Basin, Wilkes Land, Wilhelm II Land and at Law Dome. Aside from the deep records at Law Dome that stretch back tens of millennia, most records in the Australian Antarctic Territory are short, covering typically a few decades.

The Wilkes Land ITASE work of this past season developed from previous Australian work in the region; ANARE glaciological traverses in the 1980s were precursors to ITASE, producing an array of shallow cores 30–60 m deep from 95°E–135°E longitude giving climate records spanning the mid-to-late twentieth century.

Now, some 20 years after the previous ANARE fieldwork in eastern Wilkes Land, the region has been revisited. The 147 m core retrieved in the 2003–04 season should allow a detailed record of climate changes in the area for the last two to three centuries. This record will be longer than earlier records in the region, but crucially, it will also increase the period during which ice core climate record overlaps meteorological record by 20 years. This is double the previous period of overlap and it allows much better comparisons between the two types of climate information.

The reason for selecting the drilling site GD17, approximately 200 km inland of Porpoise Bay (some two-thirds of the way from Casey to Dumont d'Urville), lies in the interacting influences of ice sheet topography and Southern Ocean atmospheric circulation on the snow accumulation.

The 1980s ice cores from this region show a well-preserved climate signal: a factor that is not universal, depending upon rate of snowfall and re-working of the surface by wind.

Also, the earlier work suggests an intriguing transition eastwards in Wilkes Land, from a regional maritime climate signal that is similar to that recorded at Law Dome, (to the west) to a signal that appears to be related quite strongly to a see-saw in sea level pressure over the Southern Ocean near Macquarie Island and the Ross Sea. This transition may be the result of the influence of persistent high pressure systems south of eastern Australia and their influence on atmospheric circulation over Wilkes Land, producing strong katabatic outflow as cold air sinks down the west side of the ice sheet ridge between Dome C and Dumont d'Urville.

The climate record from this site should provide a valuable comparison with other data from Law Dome, and a useful extension of recent findings, including the ability to track past changes in sea ice and sea level pressure.

The season provided an exciting new insight into the benefits that intra-continental air transport can bring: in this case the ability to retrieve an ice core from such a remote site in just two weeks off-station. It was not without its challenges however, as a late-season window and accompanying poor flying conditions demanded modification to the work-plan. A second long ice core in the region, which was called for in the scientific plan, was not obtained in this season. Nevertheless, the wealth of data from the one long core and several short cores obtained in 2003–04 will undoubtedly provide new and exciting results, and the aerial reconnaissance undertaken this year will benefit a re-visit of the area for that second core!

The ice cores are currently being analysed in the Glaciology Laboratory in Hobart, by scientists from the two organisations.

Tas van Ommen, Glaciology Program, AAD & ACE CRC, Ian Goodwin, University of Newcastle, and Barbara Smith, Glaciology Program, AAD & ACE CRC