Warm water delays Alaska sea ice
Ocean heat retained after record highs has prevented usual freeze
The US research vessel Sikuliaq can break through ice as thick as 75cm. In the Chukchi Sea northwest of Alaska this month, which should be brimming with floes, its limits likely won’t be tested.
University of Washington researchers left Nome on November 7 on the 80m ship, crossed through the Bering Strait and will record observations at multiple sites including Utqiagvik, formerly Barrow, the United States’ northernmost community.
Sea ice is creeping toward the city from the east in the Beaufort Sea, but to find sea ice in the Chukchi, the Sikuliaq would have to head northwest for about 320km.
In the new reality of the US Arctic, open water is the November norm for the Chukchi. Instead of thick, years-old ice, researchers are studying waves and how they may pummel the northern Alaska coastline.
“We’re trying to understand what the new autumn looks like in the Arctic,” said Jim Thomson, an oceanographer at the UW Applied Physics Laboratory.
Sea ice in the Chukchi Sea every day since mid-October has been the lowest on record, said Rick Thoman, a climate expert at the University of Alaska Fairbanks’ International Arctic Research Centre and a former National Weather Service forecaster.
For example, the National Snow and Ice Data Centre on November 7 recorded sea ice at 102,000sq km, about onesixth of the typical ice extent for that date from 1981 to 2010, Thoman said.
Low ice is a problem for people of the coast. Communities north and south of the Bering Strait rely on nearshore ice to act as a natural sea wall, protecting land from erosion during winter storms.
Sea ice is a platform from which to catch crab or cod in Nome, a transport corridor between villages in Kotzebue Sound and a work station on which to butcher walrus.
The cold, salty water underneath ice creates structure in the water column that separates Arctic species from commercially valuable fish such as Pacific cod and walleye pollock. When sea ice melts, it creates conditions important for the development of micro-organisms at the base of the food web.
And then there’s wildlife. Sea ice is the prime habitat for polar bears and the preferred location for dens where females give birth. Female walruses with young use sea ice as a resting platform.
The formation of sea ice requires the ocean temperature to be about -1.8 C, the freezing point of saltwater. Historically, ice has formed in the northernmost waters and been moved by currents and wind into the southern Chukchi and Bering Seas, where it cools the water, letting even more ice form.
Climate warming has brought a harsh new reality.
High summer temperatures have warmed the entire water column in the Bering and Chukchi Seas.
Water temperatures from the surface to the ocean bottom remain above normal, delaying ice formation.
“We’ve got a cold atmosphere. We’ve got a strong wind. You’d think we’d be forming ice, but there’s just too much heat left in the ocean,” said Andy Mahoney, a sea ice physicist at the University of Alaska Fairbanks’ Geophysical Institute.
The water potentially is warm enough to melt ice moving south from northern locations.
“I haven’t seen any direct observations where ice has been transported into the Chukchi Sea and then melted,” Mahoney said. “But the water temperature maps that I’ve seen, they’re still significantly positive in Celsius. And you can’t grow ice, even if you bring ice in, if the water temperature is above freezing, that ice is ultimately going to experience melting from the water temperature.”
Thomson and other scientists on the Sikuliaq will look at how the changes could affect coastlines, which already are eroding. Less ice and more open water translate to a significant threat. Ice acts as a smothering blanket, keeping down the size of waves. Open water increases fetch, the distance over which wave-generating winds blow.
“We know from other projects and other work that the waves are definitely on the increase in the Arctic,” Thomson said.
That means even more erosion, the chance of winter flooding in villages and increased danger to hunters in small boats and longer distances for them to travel to find seals and walruses. —