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Polynyas are areas of persistent open water where we would expect to find sea ice. For the most part, they tend to be roughly oval or circular in shape, but they can be irregularly shaped, too. The water remains open because of processes that prevent sea ice from forming or that quickly move sea ice out of the region. There are two types of polynyas (described below), differentiated by the mechanism of ice removal. One process often dominates in a given polynya, but both can occur.
he Weddell Polynya is reasonably well understood. "The Southern Ocean is strongly stratified. A very cold but relatively fresh water layer covers a much warmer and saltier water mass, thus acting as an insulating layer," explains Prof. Dr. Mojib Latif, head of the Research Division at GEOMAR.
Under certain conditions, the warm water of the lower layer can reach the surface and melt the ice. "This is like opening a pressure relief valve - the ocean then releases a surplus of heat to the atmosphere for several consecutive winters until the heat reservoir is exhausted," adds Professor Latif.
Yet two major questions remain: how often does the polynya occur and does climate change influence this process?
Scientists believe the polynya is formed because of the deep water in the Southern Ocean being warmer and saltier than the surface water. Ocean convection occurs in the polynya by bringing warmer water to the surface, which then melts the sea ice and prevents new ice from forming.
The harsh winter in Antarctica makes it hard to find holes like this one, so it can be difficult to study them. This is the second year that a polynya formed, though last year’s hole was not as big. Scientists knew to monitor the area for polynyas this year because of last year’s discovery.
The deep water in that part of the Southern Ocean is warmer and saltier than the surface water. Ocean currents bring the warmer water upwards, where it melts the blankets of ice that had formed on the ocean’s surface. That melting created the polynya.
Since the hole continually exposes the water to the atmosphere above, it is difficult for new ice layers to form. When the warmer water cools, on contact with the frigid temperatures in the atmosphere, it sinks. Then it reheats in deeper areas, allowing the cycle to continue.
Moore says they are working to understand what is triggering the formation of these holes again after so many years. He thinks it is likely that marine mammals could be using this new opening to breathe.