Patches of open water in the Arctic that develop in the spring, including polynyas and widening shore leads, are largely due to the actions of wind and currents on mobile pack ice rather than ice melt. Contrary to concerns expressed about possible negative implications of these early patches of open water, these areas have always been critical congregation areas for Arctic seals and are therefore important feeding areas for polar bears in late spring.

Stirling and colleagues discussed decades ago why these areas of open water can be so important in the Southern Beaufort Sea area (Stirling et al. 1981:54):

“One useful approach is to ask what would happen if the polynya was not there? Obviously this is impossible to evaluate on an experimental basis, but by examining the consequences or natural seasonal variation, some useful insights can be gained. For example, the influence of rapidly changing ice conditions on the availability of open water, and consequently on populations of seals and polar bears, has been observed in the western Arctic. Apparently in response to severe ice conditions in the Beaufort Sea during winter 1973-74, and to a lesser degree in winter 1974-75, numbers of ringed and bearded seals dropped by about 50% and productivity by about 90%. Concomitantly, numbers and productivity of polar bears declined markedly because of the reduction in the abundance of their prey species. If the shoreleads of the western Arctic or Hudson Bay ceased opening during winter and spring, the effect on marine mammals would be devastating.” [my bold]

Dunbar (1981:32) had this to say about Hudson Bay’s persistent flaw leads:

“The largest flaw leads normally found in Canada are in Hudson Bay. The Hudson Bay lead, seaward of the fast ice, is so wide as to have generated the belief that the whole of the bay, except for the fast ice region along the shore, stayed unfrozen all winter…In the Hudson Bay instance, the myth of an open bay all winter was dispelled by Hare and Montgomery (1949), who showed that the pattern of of air temperatures over the whole region made an open Hudson Bay in winter very improbable. By overflying the area, they demonstrated that in fact the central bay is covered with ice in winter, although there normally exists a large flaw lead seaward of the fast ice on both sides of the bay and extending into northern James Bay. This flaw lead varies in width according to the direction of the wind from “about a mile and a half to 30 or 40 nautical miles” (Hare and Montgomery 1949).” [my bold]

More than 60 years ago, Hare and Montgomery (1949:160, 163) described the formation of a wide shore lead that formed in eastern Hudson Bay in early May 1948:

“The shore lead, which seems to have caused so much confusion in estimating the ice cover of Hudson Bay, may at times be entirely absent. Along the east coast from Great Whale River to Port Harrison the “Ice” reconnaissance of 8 March 1949 found no suggestion of open water. There were traces of old refrozen leads but none of them as large or as continuous as the one found along this same coast by the “Cariberg” reconnaissance of 6 May 1948. At that time the lane of open water off Port Harrison [now called Inukjuak, on the east coast] was 25 to 30 miles wide and seemed to stretch north and south along the coast as far as could be seen. It should be noted that this wide shore lead resulted after several days of NE winds which had effectively driven the ice offshore. [my bold]

See previous posts herehere, and here.

Canadian Arctic Daily Sea ice at 21 May 2021 (and years previously to 2013)


Dunbar, M.J. 1981. Physical causes and biological significance of polynyas and other open water in sea ice. In: Polynyas in the Canadian Arctic, Stirling, I. and Cleator, H. (eds), pg. 29-43. Canadian Wildlife Service, Occasional Paper No. 45. Ottawa.

Hare, F.K. and Montgomery, M.R. 1949. Ice, Open Water, and Winter Climate in the Eastern Arctic of North America: Part II. Arctic 2(3):149-164. Pdf here.

[see also: Hare, F.K. and Montgomery, M.R. 1949. Ice, Open Water, and Winter Climate in the Eastern Arctic of North America: Part I. Arctic 2(2):79-89. ]

Stirling, I. and Cleator, H. (eds). 1981. Polynyas in the Canadian Arctic. Canadian Wildlife Service, Occasional Paper No. 45. Ottawa.

Smith, M. and Rigby, B. 1981. Distribution of polynyas in the Canadian Arctic. In: Polynyas in the Canadian Arctic, Stirling, I. and Cleator, H. (eds), pg. 7-28. Canadian Wildlife Service, Occasional Paper No. 45. Ottawa.

Stirling, I, Cleator, H. and Smith, T.G. 1981. Marine mammals. In: Polynyas in the Canadian Arctic, Stirling, I. and Cleator, H. (eds), pg. 45-58. Canadian Wildlife Service, Occasional Paper No. 45. Ottawa. Pdf of pertinent excerpts of above papers here.

via polarbearscience

May 23, 2021