Arctic and Alaska Sea Ice
Mid-February 2023 Update
Sea ice is an important component of the Earth environmental system at all levels, from pan-Arctic down to the local scale. For Alaska, with the return of the sun, people will be out on the ice and working in icy waters, so I’ll provide periodic posts as we go through the season. I share this type of information more frequently on Mastodon: @AlaskaWx@mastodon.social
Sea Ice in the Arctic
For the Arctic as a whole, the February 10th sea ice extent was the third lowest since 1979 in National Snow and Ice Data Center passive microwave data: only 2017 and 2018 were lower at this point in the season. The Barents Sea sea ice extent is the second lowest since 1979 and there is even significant areas of open water poleward of 80°N, north of Svalbard and the Franz Josef Land archipelago. Sea ice extent is also below normal in the Sea of Okhotsk, though not as extreme as last winter. In the Bering Sea the sea ice extent is very close to average for this point in the season.
A great resource for keeping up with what’s happening with all things Arctic sea ice are the many Arctic sea ice graphics that Zach Labe (Princeton U.) produces. Many of the graphics are updated daily and all are posted on his website, and you can follow Zach on Mastodon at @ZLabe@fediscience.org.
Sea Ice Around Alaska
Sea ice around Alaska is fairly typical for recent years. Figure 2 shows the AMSR2 (Advanced Microwave Scanning Radiometer 2) passive microwave sea ice concentration for February 10th. A well defined ice edge runs from Bristol Bay to south of St. Matthew Island then northwest to the Russian coast. North of the ice edge in the Bering Sea, areas of lower concentration ice are primarily found on the south and west side of land areas, where frequent north to northeast winds have moved ice away. These low ice features (sometimes called Polynya) are not infrequent at this time of year and are important part of the northern Bering Sea ecosystem and for communities accessing ocean food resources. However, social media reports from the Norton Sound area indicate that shorefast ice has not set-up at some communities, and that is unusual for mid-February and may impact spring subsistence activities. North of the Bering Strait there are only a few areas of lower concentration ice, which again is pretty typical for mid-February.
Sea ice extent is a different measure of sea ice than concentration. Sea ice extent is binary: either yes there is ice or no there isn’t. By convention, a sea ice concentration of 15 percent is used as the threshold. Figure 3 shows the daily sea ice extent in the Bering Sea each winter 1978-79 to this winter from the NSIDC Sea Ice Index. Extent is slightly but not dramatically below the 1991-2020 median but is notably lower than this date last year. Ups and downs in the total Bering Sea ice extent this time of year are normal as ice is pushed around by winds. It’s likely that the maximum Bering Sea sea ice extent will be reached within the next five weeks, though there have been a few years, mostly recently in 2016, when the maximum extent was not reached until early April.
Unlike sea ice extent, reasonably reliable sea ice thickness has been available through satellite-derived products only in the past 20 years or so, and even shorter for reliable estimates of thin (less than one meter) ice thickness. During the cold season the Alfred Wegener Institute combines sea ice measurements from two different satellites (for more information see Technical details at the end of this post). Cold weather and moderate winds in early February have allowed ice to thicken up in the northern Bering Sea relative to the 2011-2022 median, but ice remains significantly thinner than median along the Chukchi Sea coast north of Cape Lisburne.
