Explaining the mystery of polynyas
High in the northern reaches of Baffin Bay, between Ellesmere Island and Greenland, where during winter one might expect to find nothing but sea ice as far as the eye can see, there is an area of open water about the size of Lake Superior. It’s called the North Water Polynya, and like all polynyas, it’s a geographically fixed
The story of the Northern Hemisphere’s largest polynya
region of largely unfrozen ocean surrounded by sea ice. What makes the approximately 80,000-square-kilometre North Water special, however, is that it’s the largest of the Canadian Arctic’s 23 polynyas, the largest polynya in the Northern Hemisphere and the most biologically productive ecosystem north of the Arctic Circle.
Coastal polynyas form when wind and currents push ice away from a coastline or a mass of fixed ice. Open-ocean polynyas form when relatively warm water upwells from the ocean’s lower depths to the surface, slowing or preventing the formation of ice. The North Water is a combination of the two types, but is primarily a coastal polynya.
In September and October, sea ice from the Arctic Ocean builds up in Nares Strait, eventually blocking the strait (1) at Smith Sound. Northerly winds (2) and the Arctic Ocean current (3) move ice into central Baffin Bay, leaving its northernmost portion relatively ice-free. Constant upwelling (4) of warmer, nutrient-rich water from the Atlantic Ocean, via the West Greenland Current (5), prevents the centre of the polynya from freezing completely, providing an overwintering habitat for species that include belugas, bowhead whales (6), seals and polar bears. It also supports a plankton bloom beginning in early April that helps sustain Arctic cod, a keystone species in the polynya’s ecosystem. The abundant marine life has for millennia provided a hunting ground for Inuit and, between the 15th century and the 19th century, European whalers, who hunted the bowhead whale nearly to extinction. From late March to early April, the North Water expands south and west toward Ellesmere, Devon and Baffin islands. By July, it reaches its maximum size of 85,000 square kilometres. By August, it’s indistinguishable from the rest of Baffin Bay, which at that point is mostly ice-free.
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