Open water in the Bering Sea for the second winter in a row
Autumn 2018 began with very warm ocean temperatures in the southern Chukchi and Bering Seas. Again, this resulted in the very late formation of sea ice.
Sea ice cover in the Bering sea during November 2018 was the least extensive on record in the satellite era since 1978. Freeze-up of the Chukchi Sea was about two weeks later than the long-term average date.
Passage of storms in December 2018 and early January 2019 produced frequent north winds and seasonably cold temperatures in the Bering and Chukchi seas. This combination allowed for the rapid southerly expansion of sea ice from the Bering Strait region. Coastal communities could expect more extensive spring ice, as had been normal in years past.
Severe storms batter sea ice
The weather pattern changed dramatically in late January 2019. For the next five weeks, 15 distinct storm systems rolled across the central and western Bering Sea from the southwest to the northeast This “parade of storms” brought seemingly non-stop south to southeast winds that decimated existing sea ice with large swells, above-freezing temperatures, and/or by pushing the ice northwards.
Impacts of this physical assault on the sea ice have been apparent in the Bering Sea, Bering Strait, and southern Chukchi Sea. February 2018 had seen sea ice extent in the Bering Sea of just 42% of the 1981–2010 average, by far the lowest of record. The February 2019 extent was 56% of average, and through mid-month, the March extent was lower than even 2018.
People must quickly alter food-gathering strategies to provide for the nutritional, cultural, and economic needs of their families.
The lack of sea ice in 2017-18—and now 2019—has had large repercussions on the northern Bering Sea marine ecosystem. With so little ice left in the Bering Sea in March 2019, this summer will feature considerably warmer than normal ocean temperatures in the Bering and southern Chukchi seas.
Environmental issues likely to result from a second year of open water conditions include changes to the entire northern Bering Sea ecosystem that may force seabirds, fish, and marine mammals to move north.
We don’t fully understand the impacts of this winter’s low sea ice and warmer ocean temperatures on marine mammal behavior. Coastal communities with active maritime subsistence activities will be the first to see these impacts.
Sea ice concentration
One tool used to determine sea ice concentration is the Advanced Microwave Scanning Radiometer 2 (AMSR-2), which measures ice concentration from aboard the GCOM-W1 satellite. Above: AMSR-2 images made on March 1, 2013 (considered normal sea ice conditions), 2018, and 2019. Purple/red = more sea ice. Green/blue = less sea ice.
Sea ice data courtesy University of Bremen. Graphics by Rick Thoman, ACCAP/@AlaskaWx.
Why did so little ice form? Warmer water, more wind
- Warmer ocean water. Ocean surface temperatures were far above normal during the summer and fall 2018.
- Warmer water = less ice. Warmer ocean surface temperatures resulted in very slow ice growth in November. Ice cover expanded in December and the first half of January, but was thinner than usual due to the increased heat in the underlying water.
- Why is the Bering Sea warmer? Open water absorbs more heat than ice-covered water. Less sea ice means warmer ocean water, and warmer ocean water generally means less and thinner sea ice. Also, warmer water recently traveled into the Bering Sea from the south, driven by wind patterns that caused North Pacific waters to heat up strongly.
Left: Sea surface temperatures (departures from normal), fall 2018. Red = warmer ocean temperatures. Blue = Colder ocean temperatures.
- More south wind. South winds were much stronger than normal from late January through early March 2019.
- Wind patterns shifted. December and early January saw north to northeast winds prevailing over the Bering Sea. However, the dramatic turn in the weather pattern brought nearly non-stop south to southeast winds across the eastern Bering Sea from January to March. February’s dramatic shift to persistent south winds was very unusual, but not unprecedented. The winter of 1988–89 saw a similar flip-flop in the weather pattern, with strong and persistent south winds across the region.
- Storms broke the ice. Because of these storms, any ice that formed quickly broke up. This was particularly true in areas where thick sea ice was never able to develop.
Left: Wind speed, January–March 2019. Red/orange = strongest winds. Blue/purple = weakest winds.
How did this past winter compare?
The amount of sea ice in the Bering Sea was lower this winter than in any year since 1850, except for 2018—and March 2019’s ice extent was even lower than 2018’s. This means that ice had disappeared from an area equal to one quarter of the size of the entire state of Alaska.
What’s next for spring/summer 2019, and beyond
We can expect that Bering Strait sea ice conditions will continue to change. Further reductions in sea ice will impact travel, subsistence uses, and safety. It is therefore essential to learn to plan for and adapt to these changes.
Cooler and less stormy weather during mid-March has allowed thin ice to reform. However, rapidly increasing heating from the sun and renewed south winds will quickly melt this new ice. It is nearly certain that 2019 will see one of the earliest melt-outs of Bering Sea ice.
Communities need to prepare for more winters with low sea ice and stormy conditions. Although not every winter will be like this one, there will likely be similar winters in the future. Ice formation will likely remain low if warm water temperatures in the Bering Sea continue.
Bering Strait on the web
- National Weather Service Alaska Sea Ice program Current sea ice conditions off Alaska’s coasts.
- National Weather Service Alaska Current Alaska weather and marine forecasts.
- Sea Ice for Walrus Outlook Weekly outlooks for sea ice. Subscribe for SIWO reports by email.
- Alaska Arctic Observatory & Knowledge Hub Observations by coastal community observers.
Thanks to our partners
This summary was brought to you by IARC, the Alaska Center for Climate Assessment and Policy, and Alaska Sea Grant. Questions or comments? Please contact Rick Thoman, ACCAP Climate Specialist, 907-474-6286