IN­FO­GRAPHIC

Ex­plain­ing the mys­tery of polynyas

Canadian Geographic - - CONTENTS - By Michela Rosano

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.

TYPES

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.

FOR­MA­TION FACTS

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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