Melt season update – Bering Sea ice abundant & Davis Strait ice 2nd highest since 1971

Polar bear habitat in the eastern Bering Sea has expanded since the official spring “maximum extent” was called for late February, and Davis Strait sea ice is tied for 2nd highest since 1971 for this week. Both regions have healthy polar bear populations and spring conditions suggest this will continue into this year.

Rode and Regehr 2010_Chukchi_report2010_Fig1_triplets_labelled

Although the melt season is underway, as of yesterday (22 April, Julian day 112) overall Arctic sea ice extent (Fig. 1) was higher than it was on the same date in 2014, 2007, and 2004 (see also Fig. 2). Despite the record low extent in February (Fig. 3), that pessimists at Polar Bears International suggested was relevant to polar bear heath and survival, I showed that was misleading.

Figure 1. Sea ice extent at 22 April (Julian day 112) for 2015, at 13.976 mkm2, was well within 2 standard deviations and higher than 2007 (shown) as well as 2004 and 2014 (not shown – see it for yourself here).

Figure 1. Sea ice extent at 22 April (Julian day 112) for 2015, at 13.976 mkm2, was well within 2 standard deviations and higher than 2007 (shown), as well as higher than 2004 and 2014 (not shown – see it for yourself here). Click to enlarge.

Sea ice maps and charts tell the story of current polar bear habitat throughout the Arctic.

Figure 2. Sea ice extent at 22 April 2015 (13.976 mkm2), courtesy NSIDC. Note Bering Sea ice is about average, top left of map, but ice in Davis Strait in Eastern Canada (bottom centre) is well above average.

Figure 2. Sea ice extent at 22 April 2015 (13.976 mkm2), courtesy NSIDC. Note Bering Sea ice is about average, top left of map, but ice in Davis Strait in Eastern Canada (bottom centre) is still well above average. Click to enlarge.

Figure 3. Sea ice extent at 25 February, when a “record low” maximum called for 2015 by NSIDC, at 14.54 mkm2). Although there was some melt, the ice was back up to 14.453 mkm2 by 26 March. Note that both extents round to 14.5 mkm2 (i.e., not statistically different), creating what NSIDC called a “double dip” maximum extent. They are, however, sticking to the February date as the official 2015 spring maximum.

Figure 3. Sea ice extent at 25 February, when a “record low” maximum called for 2015 by NSIDC, at 14.54 mkm2). Although there was some melt, the ice was back up to 14.453 mkm2 by 26 March. Note that both extents round to 14.5 mkm2 (i.e., not statistically different), creating what NSIDC called a “double dip” maximum extent. They are, however, sticking to the February date as the official 2015 spring maximum. Click to enlarge.

Following up from last week’s sea ice update, it’s worth noting that Bering Sea ice (which is naturally quite variable) often does not reach its maximum extent until late April, a month or so after the Arctic as a whole is at its maximum extent in late March. That means plenty of ice for the next month or so in the Bering Sea, from which Chukchi Sea polar bears can hunt baby seals. After that, in June and perhaps part of July, the sea ice feeding platform will be over the Chukchi Sea proper. Fattening up time for Chukchi Sea polar bears.

Fat polar bears will be well-equipped for a few months of fasting over the coming summer, whether they are on land or on the ice. The last report on Chukchi Sea polar bears captured in early spring (mid-March to mid-May), where polar bears are known to “occasionally occupy ice as low as 15% concentration (Rode et al. 2014:79), showed they were some of the fattest bears in the Arctic and reproducing well (Rode et al. 2013, 2014; Rode and Regehr 2010). These characteristics are accepted indicators of a healthy population — Chukchi bears were doing better in 2011 than they were doing in the 1980s.

The researchers got this result despite the marked decline in extent of summer sea ice in the Chukchi Sea in 2011 compared to 1986 (which included the 2nd lowest (2007) extent since 1979), and in marked contrast to the expectation that the bears would be found to have “reduced body condition” and “decreased reproduction and/or cub survival” as a result (Rode et al. 2013).

As I commented two years ago:

“It’s certainly going to be hard to make a case that polar bears are starving and dying because of global warming if the bears aren’t starving or dying, but getting fatter instead.”

From the 2010 interim report by the study’s investigators (Rode and Regehr 2010:4):

“…three adult males weighed over 1200 lbs and the heaviest bear was 1353 lbs, which is a record for spring research in Alaska.”

So much for summer ice extent being the critical indicator of polar bear health in the Chukchi Sea!

Over in Davis Strait, 2015 is tied for 2nd highest extent for this week (along with 1983 and 1993) – last year (2014) was the highest. The long-term trend since 1971 calculated by the Canadian Ice Service for ice coverage this week in Davis Strait is increasing (Fig. 4, below).

Figure 4.

Figure 4. Sea ice extent for Davis Strait from 1971 to 2015, for the week of 23 April. Long-term trend line, mean, and average calculate by CIS. See red inset map upper left for area covered. Click to enlarge.

For the Canadian East Coast as a region, ice is well above average for this date (note the quasi-decadal undulating pattern since 1969, from above average to below and back, although this has not been quite so pronounced since the early 2000s):

Figure 5.

Figure 5. Sea ice extent in Eastern Canada from 1969 to 2015, for the week of 23 April. See red inset map upper left for area covered. Click to enlarge.

Sea ice is still below average in the Barents Sea (below) due to the state of the cyclical Atlantic Multidecal Oscillation (AMO), but there is still quite a bit of ice for polar bears to use as a platform for hunting seals.

Figure 6.

Figure 6. Barents Sea ice concentration at 22 April 2015. Original here. Click to enlarge.

References
Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2013. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Oral presentation by Karyn Rode, 28th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK. Abstract below, pdf here.

Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014 [in print]. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract 

Rode, K. and Regehr, E.V. 2010. Polar bear research in the Chukchi and Bering Seas: A synopsis of 2010 field work. Unpublished report to the US Fish and Wildlife Service, Department of the Interior, Anchorage. pdf here.

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