Tag Archives: thickness

Does thick first year ice on Hudson Bay mean a late date ashore for WH polar bears in 2018?

Following up on my previous post, it appears sea ice conditions on Hudson Bay this year might be headed for a late breakup due to the dominance of thick first year ice. That would mean a relatively longer on-ice season for polar bears in Western and Southern Hudson Bay.

James Bay female and cub_Ontaro Govt

As of the 1st week in May 2018, most of Hudson Bay, Foxe Basin and Hudson Strait were covered with thick 1st year ice (dark green, >1.2 m thick):

Hudson Bay weekly stage of development 2018 May 7

Compare that to the 1st week of May 2016, which had much less thick first year ice than 2018 and more medium first year ice (70-120cm, bright green):

Hudson Bay ice stage of development weekly at 9 May 2016

To update the situation, at the end of May this year (week of 28 May), thick first year ice covered even more of the bay with a large patch of open water in the NW corner:

Hudson Bay weekly stage of development 2018 May 28

Thick first year ice does not melt as quickly as medium or thin first year ice (lime green) under most conditions, so the amount of thick first year ice present in May strongly affects the rate of breakup of the ice over the summer (temperature and wind also contribute). Here are some charts of ice melt sequences from the past (2016 and a couple others) that give a hint at what might be in store for Hudson Bay polar bears this year.

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Polar bear habitat update early spring 2018

Spring in the Arctic is April-June (Pilfold et al. 2015). As late April is the peak of this critical spring feeding period for most polar bear populations, this is when sea ice conditions are also critical. This year, as has been true since 1979, that sea ice coverage is abundant across the Arctic for seals that are giving birth and mating at this time as well as for polar bears busy feeding on young seals and mating.

Polar_Bear_male on sea ice_Alaska Katovik Regehr photo_April 29, 2005_sm labeled

Below is a chart of sea ice at 25 April 2018, showing sea ice in all PBSG polar bear subpopulation regions:

masie_all_zoom_4km 2018 April 25

Some Arctic subregions below, in detail. Continue reading