Ice maps vs. observations in the W. Arctic – polar bear habitat reality check

Last Wednesday (8 June 2016), the US Coast Guard rescued walrus hunters from Shishmaref in the Bering Strait who got stuck in sea ice that is barely visible on sea ice maps. It’s a rare glimpse of what sea ice really looks like up close compared to what you see on the ice maps.

Watch the video here: https://www.dvidshub.net/video/embed/467959

[Unfortunately, the screencaps from the video, like the one below, are less impressive than the film. In the video, you can see the hunters walking on the ice around their trapped boat – the ice does not visibly move]

Have a look at the sea ice maps below for the day the incident took place. They show what appears to be hardly any ice in the area.

This is a good lesson for assessing what’s been going on in the Beaufort Sea a bit further east, where winds and currents have opened up a rather large patch of open water surrounded by considerable expanses of sea ice – at issue is the possible impact on polar bear spring feeding for April and May.

Coast Guard rescues walrus hunters stranded in sea ice off Western Alaska (Alaska Daily News, Jerzy Shedlock; 9 June 2016):

“Kodiak-based Coast Guard crews rescued six hunters from two skiffs that were stranded near the Western Alaska island village of Shishmaref early Wednesday morning.”

Close-up of the Chukchi/Beaufort region at 8 June 2016 (rotated), of Masie NSIDC sea ice map:

Masie NSIDC sea ice map at 8 June 2016, original “daily image”- as you can see, the bit of ice off the Alaskan coast of the Bering Strait at Shishmaref is barely visible. Yet it was dense enough for hunters to expect to find walrus and thick enough to get them so stuck they needed rescue.

Compare the above with the 21 May 2016 image (copied below, original here) included in the May NSIDC sea ice report showing ice levels in the Beaufort Sea this year. Note the rather extensive ice still in place along the coast, almost certainly enough to allow polar bears to hunt seals:

The NSIDC report reiterates the fact that the open water in the Beaufort is “a result of strong wind-driven divergence throughout the late winter and spring.”

In other words, the ice has not melted, it has been driven offshore. As this appears to be a phenomenon that has not happened this early in the season since 1979, there is no basis for suggesting that it presents a threat to polar bear survival.

As I pointed out a few weeks ago, USGS maps of polar bears tagged in the Beaufort Sea show most bears positioned around the edges of the open water – precisely where you would expect to find seals in a region dominated by multiyear ice.

Most of the ice in the Beaufort Sea is still classified as multiyear ice, as the Canadian Ice Service map (below) for the week of 6 June 2016 shows (all the brown is “old” ice > 1 yr):

As I discussed last year, a regular occurring patch of open water known as the Cape Bathurst polynya usually forms in this region and it’s where bearded seals in particular congregate to have their pups and mate because they need open water nearby in order to continue feeding (Stirling and Cleator; Stirling et al. 1981).

One of the images I included in that post (read the whole thing here) compared the polynya as seen at 28 May 1975 (Smith and Rigby 1981) vs. 14 May 2015, copied below:

Also from last years post:

Here is what Smith and Rigby (1981:24) had to say about the development of open water in eastern Beaufort in the spring:

“Some open water can be found in virtually all months somewhere in western Amundsen Gulf in the area of Cape Bathurst, Cape Parry, and Cape Kellet (Banks Island). Open water can appear as early as sometime in December, although it is not until April that a characteristic form to the polynya appears.

…

Open water remains in the general area, in some form, until late May to early June when, characteristically, the area between Cape Bathurst and Cape Kellett opens up to form a disintegration area. Until April, the size, shape, and location of open water is quite variable by month and by year (e. g. Fig. 14b). …The extent to which the shorelead polynya system in the Beaufort Sea is open is mainly dependent upon wind since this influences the movement of the Arctic pack. The coast was open to Mackenzie Bay in all five summers, and as far west as Barter Island in three.” [my bold]

It’s also usual to see open water to the west, around Barrow (Smith and Rigby 1981; Dunbar 1981), as the image below shows:

And while clearly this year the amount of open water is much larger than 2015 or 1975, there is no reason to suppose that conditions in 2016 (see image ) will be catastrophic for either seals or polar bears. Compare the image (below) 2016 conditions at about the same time in May as in the images above:

Right now, in early June, the amount of sea ice in the Beaufort over time (courtesy Canadian Ice Service) shows that in 2016, the ice is indeed the lowest it’s been since 1968 – but that until this year, 1998 and 1970 were virtually tied for having the least amount of ice (week of June 4):

Conclusion: What any of this means for polar bears and Arctic seals remains to be seen.

References
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.

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.