A long wait for sea ice

Hudson Bay is part of what’s called the “seasonal” sea ice ecoregion. The bay freezes over completely every winter and melts out completely every summer, forcing the resident polar bears on shore with nothing of substance to eat, as their main prey, seals, are inaccessible. Polar Bears International is monitoring this “ice-free” summer period closely to infer the well-being of bears. This summer, sea ice broke up relatively early in Western Hudson Bay, on June 18. Then, North America and Hudson Bay specifically had their warmest fall on record (Fig. 1), fueled by a combination of human-made climate change, a budding La Niña event in the Pacific, and some random weather variations.

As a result of the warmth, sea ice in Hudson Bay was very slow to grow and it took until November 26 for sea ice sufficient for that bears to walk on to form near Churchill, Manitoba. By December 7, Western Hudson Bay was covered by 30% sea ice, marking the official end of this year’s ice-free period, which came in at 172 days (Fig. 2). This is the second-longest such period since reliable satellite monitoring began in 1979. Back in the 1980s, the average ice-free period was 124 days – today it’s well over a month longer.

What happened this year in Hudson Bay was not an isolated event. Several ocean basins in the Eastern Canadian Arctic (Foxe Basin, Baffin Bay, Davis Strait), as well as the region around Svalbard, Norway, were and still are anomalously warm and have seen some of the slowest sea ice growth ever. This means polar bear populations in these regions will likely have a delayed start to their hunting season.

Conversely, on the other side of the Arctic, near Alaska and far Eastern Russia, this year’s sea ice has been consistent with long-term averages, illustrating the strong year-to-year and region-to-region variations typical of Arctic weather and climate. Wind patterns and ocean currents helped deposited warm air and water in some regions while diverting it from others, leading to large sea ice differences between regions and in what animals might experience this winter.

The long-term trend of Arctic sea ice is clearly downwards, as one might expect on a warming planet, but the last decade has indeed seen something of a “slowdown” in sea ice decline, especially in summer. Scientists are studying the phenomena to better understand when sea ice might enter another phase of rapid decline. So far, this winter is on track for having the smallest Arctic-wide sea ice extent on record and it will be interesting to see with how much or how little sea ice the Arctic will enter next year’s melt season.

As bears head out on the sea ice and into the dark Arctic night, we lose sight of them, but keep tracking some of them with GPS (Fig. 3) — and so can you via Polar Bear International’s bear tracker. Most polar bears tagged in Western Hudson Bay return to the same area each year, like salmon that return to their spawning grounds. This past summer, however, there was one bear from Western Hudson Bay (named E4 on the map in Fig. 3) that wandered off to the far North-East of Hudson Bay and spent the fall on Baffin Island. We are curious whether it will return South this winter once Hudson Bay freezes over again.