Sea ice in the Warming World

The world oceans are the plumbing system of our planet. Cold water is transported from the poles to the equator, where cold water warms before it is sent back to the poles. Without that mechanism the poles would be much colder, and the equator regions even warmer. But how is that circulation driven? It cannot be the sun, as warming the oceans from above stabilizes the water column. Just imagine and compare this to a pot filled with water on a heating element. Heating from below makes the water circulate, heating from above makes the surface water light and stable.

Here is what mother nature does: it makes polar surface water heavy. As sea water freezes, the salt isn't built into the crystal structure of ice, but it is rejected as brine into the cold ocean below. The constant supply of brine during freezing makes the cold water even heavier - it is sinking down to the abyssal basins of the oceans forming Antarctic Bottom water filling half of the world's oceans. The amount of brine and bottom water produced is therefore directly related to the sea ice volume, or its thickness. With thinner ice in a warming world we expect less bottom water produced, and therefore slowly cranking up the heat on our planet. But thinning and reduction of bright and snow covered sea ice also means that less sunlight is reflected back to space, cranking up the heat even more. It is therefore important that we get good numbers for sea ice thickness and snow on top of it. During the Weddell Sea Expedition, we are finding ways to improve the measurement of sea ice from space. Ultimately our research will therefore improve the climate and weather predictions in all places of the world, even far away from Antarctica where most people live.

Written by Wolfgang Rack, Gateway Antarctica, University of Canterbury, New Zealand