Tag Archives: open water

Polynya refresher: open water in spring is due to winds & currents, not ice melt

Arctic sea ice begins to open up in spring at predictable locations due to currents and prevailing winds and this was as true in the 1970s as it is today. Polynyas and widening shore leads that most often get mistaken for early sea ice melt are those in the Beaufort and Chukchi Seas and in Hudson Bay.

Beaufort Sea male polar bear USGS_2005 Amstrup photo

But 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.

Seal habitat frozen open lead_Beaufort 2008_Miller

Seals hauled out beside a lightly frozen over lead in Beaufort Sea ice, 2008. USFWS.

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Tracking polar bears in the Beaufort Sea in April 2016 and early polynya formation

putting_collar_on_polar_bear_slider_USGS

Here’s the update on the polar bears fitted with satellite collars or ear tags in the Beaufort by USGS biologists over the last two years. Five new bears were added last month, which means there are now thirteen bears being tracked. Ice conditions are somewhat different than they have been in the past but concluding that such a situation means trouble is premature, I think (see here). Continue reading

Beaufort Sea swimming polar bears far from land but not very far from sea ice

Recent accounts of an encounter with a curious polar bear female and her two older cubs in the Beaufort Sea on 16 September give contradictory details about the position of sea ice at the time. The same researcher told one reporter that the ship was 240 km from land, another that it was 240 km from the sea ice, and in another account (that he wrote himself), said the ship had been far from land and sea ice.

Beaufort swimming polar bears_Sept 30 2015_Global news

University of Victoria (Canada) chemical oceanographer Jay Cullen said on the expedition web site:

“After arriving on station and beginning work the crew noticed three polar bears in the water together which swam around to the ship when our water sampling system was nearly 3500 meters below the surface. The ship was located far from sea ice and land. Indeed, Arctic sea ice extent was the fourth lowest on record this year and there has been speculation that this imposes stress on polar bears which rely on the ice to hunt.”  [my bold]

But the maps below show that at the time of the incident (taken from the expedition web site) and the NSIDC Masie sea ice map for 16 September 2015, the ship [the CCGS Amundsen, acting as a research vessel] was actually quite close to an isolated large patch of sea ice, although further from the edge of the main pack. A patch of sea ice plenty big enough for a polar bear to rest upon – no wonder the bears did not appear stressed.

And the polar bear biologist Cullen consulted (Dr. Andrew Derocher) implied by his response that the bear was indeed far from sea ice. Reminds me of the swimming polar bear off the Hibernia oil platform off Newfoundland March 2015, which turned out to be not far from ice at all. See what you think.
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Tracking polar bears in the Southern Beaufort May 2015 – thick ice and polynyas

Polar bear habitat in the Southern Beaufort for May 2015 was a contrast between the development of recurring polynyas (patches of open water) and tremendously thick sea ice. So it’s interesting to see where the polar bears tagged by USGS biologists chose to hang out.

Polar_Bear_Biologist_USFWS_working_with_a_Bear_Oct 24 2001 Amstrup photo

The total number of bears being tracked in May – 23 – is down markedly from the 30 bears USGS biologists started with in April.

Most of the collared bears were concentrated in May along the shore lead (crack of open water) that normally develops between the shorefast ice and the pack ice offshore. That’s especially understandable this year, since most of that pack ice is 3-5 m thick (10-16 ft) – see the maps below.
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Hudson Bay sea ice coverage is atypical this year but what does that mean for polar bears?

Churchill_Polar_Bear_2004-11-15 Wikipedia

There is a rather large patch of open water in the northwest sector but what’s also unusual about breakup this year is the virtual lack of open water in eastern Hudson Bay – that almost never happens (compare to 2013 here). In addition, there’s still very little open water in Hudson Strait, which connects Hudson Bay to Davis Strait in the east – that’s also unusual.

Figure 1.  Sea ice extent over Hudson Bay and Hudson Strait at 26 May 2015. Canadian Ice Service.

Figure 1. Sea ice extent over Hudson Bay and Hudson Strait at 26 May 2015. Canadian Ice Service. Click to enlarge.

The question is: does the somewhat unusual pattern of ice cover at this date – which developed rapidly over the last few weeks – suggest we can predict whether polar bears will have a shorter-than-average hunting season?

To answer that, you have to look at maps generated by the same source over several years. The result, in my opinion, is inconclusive – while so far, this year looks a bit more like 2009 (which was a very late sea ice breakup year) than it does 2011 (which was an early breakup year), it’s really too early to tell.

I suggest we simply won’t know for another month or so which pattern will prevail. However, that hasn’t stopped IUCN Polar Bear Specialist Group member Andrew Derocher (via Twitter, e.g., here and here, among many others) from suggesting that this year’s pattern is likely a portend of doom for Hudson Bay polar bears. See what you think.
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Arctic polynyas and sea ice extent in Canada at 20 May 2015

The map of sea ice extent in Canada at 20 May 2015 is an almost-perfect example of the placement of recurring patches of open water polynyas that were present in the Canadian Arctic at this time of year in 1975-1979. Notes from field work on shore leads in Hudson Bay ice at May, 1948 offer further insight into the current pattern of sea ice cover on the bay.

Polynyas and shore leads vs sea ice at 20 May 2015_PolarBearScience

May is traditionally the time when recurring polynyas in the Canadian Arctic become more prominent and persistent shore leads (cracks in the ice near shore, also called “flaw leads”) become wider. Polar bears hunt around these polynyas because ringed and bearded seals congregate around them in the spring (Stirling et al. 1981; Stirling 1997). These polynyas are often not truly “open water” but covered by thin ice that’s easy for seals to break through.

Slight differences in location and size of polynyas and shore leads from year to year (especially in spring) are governed primarily by prevailing winds (Dunbar 1981:29) and to a lesser extent, currents. See my previous discussion on Beaufort Sea polynyas, with references: Beaufort Sea polynyas open two weeks before 1975 – open water is good news for polar bears.

This suggests that while sea ice cover over Hudson Bay and the Beaufort Sea is now a bit below average for this time of year (as the maps for this week show), it does not necessarily portend an earlier breakup or longer open-water period later in the year.

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Polar bear habitat update: Hudson Bay sea ice breakup on track

Hudson Bay sea ice coverage is only slightly below average for this time of year (week of 14 May, below) but well above levels for 2006, when Western Hudson Bay breakup was relatively early).

Sea ice Canada 2015 May 14_CIS

Figure 1. Sea ice coverage over Hudson Bay for the week of 14 May, 1971-2015. Canadian Ice Service. Click to enlarge.

Figure 1. Sea ice coverage over Hudson Bay for the week of 14 May, 1971-2015. Canadian Ice Service. Click to enlarge.

Even at its highest extent in April, Hudson Bay is only 97-98% ice covered (due to persistent shoreleads and polynyas), which means ice levels are currently only 10% or so below maximum. In other words, there is still lots of polar bear hunting habitat over the bay.

That’s a bit lower than ice coverage was for the last two years at this date (2013-2014), which had average or above average ice cover. However, there is currently a bit more ice on Hudson Bay than there was in 2011 and 2012 – and much more than there was in 2010 and 2006.
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