September 2012 Arctic summer sea ice loss record compared to September 2012 Antarctic winter sea ice expansion record. Are we witnessing the Anthropocene equivalent of the Pleistocene Arctic-Antarctic bipolar seesaw? Image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio and NASA Earth Observatory/ Jesse Allen.
While the Arctic loses sea ice at record pace, interestingly the sea ice around Antarctica shows a different behaviour. Between 1978 and 2010 it has grown by 6600 square miles (17000 sq km) on average, a new NASA release states.
What’s more: in recent years the winter sea ice growth seems to be accelerating – and just last month it reached a record high since satellite measurements began.
It is important to note there is little lasting effect. Antarctica is surrounded by open ocean – almost all the expanding winter sea ice melts away in summer – and that’s when the fronts of the actual ice sheet [land ice that is – the ice that influences sea levels] can be exposed to melting and calving.
Still it is an odd effect to have a seasonal ice growth trend anywhere on this clearly warming planet. As sea ice [in spring that would be for Antarctica] is ‘good for the albedo’ it is also something we can probably welcome as good news – and something of course we would want to understand.
Now that’s why thanks to the United States of America there is something called the National Aeronautics and Space Administration Goddard Institute for Space Studies – indeed, NASA GISS.
Ozone depletion may fuel the Antarctic winter sea ice engine
They have an interesting theory why the Southern Ocean could have increasing amounts of winter sea ice: depletion of the ozone layer over Antarctica leads to lower heat absorption in the local stratosphere (as ozone is a greenhouse gas). Therefore the (high-altitude) temperature difference with temperate regions is increasing, which in turn strengthens the Antarctic circumpolar wind.
Now imagine what happens to floating ice in these wedge-shaped seas (for instance the Ross Sea) that lie closest to the Antarctic heart land, when you have continues high speed circumpolar winds – look at the coast line and recall vectors from Physics class. Indeed, the ice gets pushed out to the open ocean.
In winter this engine drives the sea ice expansion – as old ice blows out, polynyas form along the coast, which easily freeze up again in contact with the cold air above.
Now to make a complex story even more complex: that increasing Antarctic circumpolar wind could actually also be fueling Arctic melting – as it could strengthen the Meridional Overturning Circulation (MOC) – and therefore the warm Gulf Stream.
© Rolf Schuttenhelm | www.bitsofscience.org