Outlet glaciers, fast-flowing glacial streams, carry ice from within the ice sheet to the coast, where it breaks off into the sea in the form of icebergs. The scientists studied satellite images of 175 such glaciers in the East Antarctic Ice Sheet along a 5,400-kilometre stretch of coast over the last 50 years, which reveal synchronous time periods of the advance and retreat of these glaciers’ snout position that go hand in hand with atmospheric cooling and warming. “We discovered that these outlet glaciers react very rapidly and directly to changes in the climate,” explains Professor Andreas Vieli from the University of Zurich. “This implies that, the ice sheet may be more vulnerable to global warming than previously thought.”
Despite major differences in the length change between individual glaciers, three periods with clear tendencies can be observed: In the 1970s and 1980s, the glaciers generally tended to retreat in warmer air temperatures (63 percent) while most glaciers advanced in the 1990s as the temperatures decreased (72 percent). Since 2000 the temperatures and the proportion of advancing and retreating glaciers is more even.
Ice sheet deemed climate-resistant
The East Antarctic Ice Sheet, which is up to 4,000 meters thick, has been regarded more as climate-resistant until now as it is very cold in the East Antarctic, the air temperatures on the coast are mostly well below freezing and thus only little ice melt occurs. Moreover, such outlet glaciers were also known to go through regular cycles of prolongued advances and rapid retreats due to major individual iceberg break-offs which, taken individually, seem unrelated to climate. “Consequently, the synchronous advance and retreat behavior of the glaciers observed and in tandem with fluctuations in air temperature came as a surprise to us,” says Professor Vieli. This synchronous behavior of the glaciers was only clearly visible thanks to the large number of glaciers studied and the consideration of long periods of several decades.
A more in-depth analysis of climate and glacial data then revealed that it is not the air temperature alone that influences the glaciers; the distribution of the sea ice, atmospheric circulation and ocean temperature, which are all linked to air temperature in the climate system, also seem to play a role. The data collected clearly reveals that more icebergs broke off and the glaciers tended to retreat in times of warmer temperatures and less sea ice; in cooler temperatures, the sea ice was more widespread and the glaciers tended to advance.
Further studies necessary
The results of the study suggest that outlet glaciers might react relatively quickly by retreating following a change in climate. This could enable them to attack the inland ice of the Eastern Antarctic Ice Sheet via dynamic feedback mechanisms, as can currently be observed in Greenland. This is of concern, as a total disappearance of this ice sheet would cause the sea level to rise by over 50 meters. However, the researchers urge interpreting their results with caution and stress that the behavior of these outlet glaciers needs to be studied in more detail and understood better with respect to the climate.
Miles B.W.J., Stokes C.R., Vieli A., Cox N.J.. Rapid Changes in Outlet Glaciers on the Pacific Coast of East Antarctica Driven by Climate. Nature, doi: 10.1038/nature12382