Antarctic Sea Ice: From the Megascale to Microscale--Climatic Interactions over ten
orders of magnitude
S.F. Ackley, Geol. Sciences Dept., UTSA
Antarctic sea ice at its maximum winter extent covers an ocean area the size of the
continent of South America. The recent contrast of a decreasing Arctic sea ice cover and
slightly increasing Antarctic sea ice extent will be discussed in terms of the climatic
drivers in both hemispheres. The seasonal variation of Antarctic sea ice extent from
summer to winter, increasing to five times its minimum area, has strong effects on the
radiation balance as high albedo ice covers replace darker ocean water. Heat fluxes to the
atmosphere and salt fluxes to the ocean are affected by smaller scale processes of ice
growth and decay. A mesoscale interaction (hundreds to tens of kilometers) of
importance is ice production in coastal polynyas, generally driven by more localized
wind effects, where ice production can be higher in winter as ice is removed by advection
and grows again at high open water growth rates. Ice growth processes also interact at
tens of meters to sub-meter scales by wave-driven ice formation at the ice edge and
snow-ice formation induced by snow loading, flooding and refreezing on the surface of
existing ice covers. Variations in these processes can cause thickness variations and
effects on heat and salt fluxes that upscale to the climate level. At the sub-millimeter
scales of the brine pockets within sea ice, biological and geochemical interactions take
place that modulate the flux of carbon dioxide between the atmosphere and the ocean.
Observational systems from space have supplied critical information on factors affecting
these processes at all these scales. However, field experiments have been necessary to
provide correct interpretation of remote sensing and information not discernible from
space. Illustrations of remote sensing applications and upcoming field validation efforts
will be discussed.