Tag Archives: upwelling

Polar bear specialist calls Hudson Bay freeze-up ‘late’ yet bears were moving offshore 2 weeks ago

Predictably, polar bear specialist Andrew Derocher has finally posted a tracking map of the Western Hudson Bay bears his team has fitted with collars and eartags–two weeks after bears were released from Churchill’s polar bear jail, which is the local signal that there is enough sea ice for bears to leave shore. As I reported two weeks ago, release of jailed bears happened this year on 10 November. And as I predicted in that post, by waiting so long after that event to post his map, Derocher can make it seem to his naive followers on Twitter that the bears are just starting to leave now (the last map he posted was on 11 November, when none of his bears had moved). He reinforces this by calling WH freeze-up “late”, when by all objective measures (including local informants reporting bears on the ice) it was as early as it had been in the 1980s (Castro de la Guardia et al. 2017).

Recall that fall is the second-most important feeding season for polar bears, due to the fact that seals are strongly attracted to newly-forming sea ice. It’s their chance to regain some or all of the weight lost over the summer, before the long winter fast begins (while bears indeed hunt when they can, they are not often successful during the depths of the Arctic winter: most bears are at their lowest weight by March).

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Sea ice growth after the summer minimum begins in the Canadian Arctic Archipelago

The Arctic sea ice minimum was declared to have been reached on 16 September this year (4.72 mkm2), breaking no records.

Ice extent can only go up from this point forward but at this time of year, it happens slowly and isn’t noticeable in the Arctic Basin as much as it is in the Canadian Arctic Archipelago. As I wrote about last year, new ice development in the fall next to shore creates upwelling conditions that attract fish and seals, and therefore provides feeding opportunities for polar bears.

The same process likely happens when new ice forms next to old ice. These few weeks of developing sea ice, wherever they occur, are the last chance polar bears have to replace weight lost over the summer before the cold and darkness of winter reduces hunting opportunities to virtually nil.

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