The edge of East Antarctica as you’ve never seen it before
ACE CRC sea ice scientist Alex Fraser has produced a picture of the East Antarctic coastline never seen before. His PhD research has brought together more than 125,000 satellite images to show changes in the extent of "fast ice", at a resolution of two kilometres every 20 days from 2000 to 2008.
So-called fast ice is not named for its speed. It is in fact seawater that has formed into ice and then become "fastened" to the shore or grounded icebergs. Fast ice extent and variability has global ramifications, being closely associated with global ocean circulation. Fast ice variability is also particularly significant to the life of Emperor penguins, providing them with a stable breeding platform and a place for adults to base their chicks while they forage for food in the Southern Ocean.
Mr Fraser’s research maps changes in the extent of this ice along an 8000-kilometre stretch of coastline, from 10 degrees west to 172 degrees east. The research revealed an increase in the extent of fast ice between March 2000 and December 2008 in the Indian Ocean sector of the East Antarctic coast. Given their reliance on fast ice, this may sound like good news for the penguins, but this is not necessarily the case. Research published in 2009 by Mr Fraser’s fellow ACE CRC sea ice scientist Dr Rob Massom (with Australian and French colleagues) found that an increase in the distance between the Emperor penguin breeding colony and the fast ice edge had a negative impact on Emperor penguin breeding success in Adélie Land, East Antarctica. This is because adult Emperor penguins leave their young while they traverse the ice to the ocean in search of food. An expansion in fast ice means a longer distance from the penguin colony to the ocean, giving vulnerable chicks a longer wait with empty stomachs and possibly also affecting the survival of foraging adults. Fast ice extent does, however, vary in different locations. While it has increased in the Indian Ocean sector (20-90 degrees E), no significant change was found for this time period in the Western Pacific sector (90-160 degrees E).
To allow the analysis to take place, 125,000 images, amounting to 12 terabytes of data, were acquired from the MODIS (MODerate resolution Imaging Spectroradiometer) sensor onboard NASA’s Terra and Aqua satellites. In the summer months, visible images were downloaded, while thermal infra-red images were used during winter, when the coastal zone was shrouded in darkness. Mr Fraser, who is now close to submitting his PhD, has a unique way of looking at the data: "There’s three years of my life in this picture,’’ he said.
The work is the longest time series showing broad-scale fast ice extent produced so far, and also represents the highest resolution continuous record of fast ice produced anywhere in Antarctica. In addition to its significance for Emperor penguin breeding success, the research has provided a major new dataset for use in the modelling of ocean currents and in research into factors affecting the stability of floating ice sheet coastal margins (including ice shelves and glacier tongues). The research has also allowed Mr Fraser to compare differences in the seasonal timing of changes to fast ice with seasonal changes in overall sea ice.
The next logical step is to attempt to find out what drives year on year variability in the extent of fast ice. "Factors affecting fast ice extent are poorly understood, so more work is needed to determine what drives it," Mr Fraser said. Factors to be considered include wind speed and direction, ocean and air temperature, ocean waves, nearby pack ice conditions and snow cover. Plans are also afoot to extend the coverage around the entire Antarctic coast, and into the future.