Sep 18, 2006

Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions

  • States that estimates of sea ice extent based on satellite observations show an increasing Antarctic sea ice cover from 1979 to 2004 even though in situ observations show a prevailing warming trend in both the atmosphere and the ocean
  • Explores this riddle using a global multicategory thickness and enthalpy distribution sea ice model coupled to an ocean model
  • The model simulates an increase of 0.20  1012 m3 yr1 (1.0% yr1 ) in total Antarctic sea ice volume and 0.084  1012 m2 yr1 (0.6% yr1 ) in sea ice extent from 1979 to 2004 when the satellite observations show an increase of 0.027  1012 m2 yr1 (0.2% yr1 ) in sea ice extent during the same period
  • The model shows that an increase in surface air temperature and downward longwave radiation results in an increase in the upper-ocean temperature and a decrease in sea ice growth, leading to a decrease in salt rejection from ice, in the upper-ocean salinity, and in the upper-ocean density
  • Finds that the reduced salt rejection and upper-ocean density and the enhanced thermohaline stratification tend to suppress convective overturning, leading to a decrease in the upward ocean heat transport and the ocean heat flux available to melt sea ice
  • Finds that the ice melting from ocean heat flux decreases faster than the ice growth does in the weakly stratified Southern Ocean, leading to an increase in the net ice production and hence an increase in ice mass
  • Concludes that this mechanism is the main reason why the Antarctic sea ice has increased in spite of warming conditions both above and below during the period 1979–2004 and the extended period 1948–2004