North America's biggest glacier, about 100 miles east of Prince William Sound, pours about as much fresh water into the Gulf of Alaska each year as flows from the mouth of the Nile River, according to a new study published online in the journal Geophysical Research Letters. As temperatures rise, that flow of fresh water could increase by up to 50 percent decades from now, the study said.
Seasonal melt from Bering Glacier, a nearly 120-mile-long mass of ice that sprawls over 2,000 square miles, discharged about 40 cubic kilometers of freshwater annually between 2002 and 2012, said the study, led by scientists at the Michigan Tech Research Institute.
"It's a really significant chunk of water coming out of the glacier," said Edward Josberger, a lead author of the study.
The freshwater discharge estimate was calculated with a formula that considered temperatures in Yakutat, the community nearest to the glacier's outflow, Josberger said.
"The temperature relationship is pretty robust, year to year," he said.
Projecting future temperatures, especially melting-temperature days, Josberger's team estimated that the meltwater flow could increase to as much as 60 cubic kilometers a year by 2050.
Such a large increase in freshwater flow could change dynamics in the Gulf of Alaska, Josberger said. Salt water is heavier than fresh water, so the existing meltoff helps regulate currents and other characteristics of the Gulf, he said.
The study is part of a wide-ranging program involving numerous agencies and institutions to monitor Bering Glacier, which sends its water flow into a terminus lake that is connected by river to the Gulf of Alaska.
In addition to being the biggest and longest glacier on the continent, Bering Glacier is -- right now -- the world's largest surging temperate glacier. The glacier goes through relatively long periods of retreat, punctuated by shorter surges. The current surge started in 2008 and began to slow in 2011, according to a University of Utah and University of Alaska Fairbanks study published in The Cryosphere.
Surges and retreats result from the interplay between annual snow load, snow and ice melt and gravity, Josberger said.
On a glacier so vast, different parts are moving at different times, he said. In summer, when scientists are on the surface, the complexities are evident, he said. For example, big streams can appear, dropping down into deep, slippery holes known as moulins, he said. "It's such a huge glacier, you're just lost," he said.
Among its other projects, the Michigan Tech Research Institute team has compiled a time-lapse series showing Bering Glacier's surges and retreats from 1984 to 2012.
Smaller tidewater glaciers in Alaska, meanwhile, are generally retreating, but exhibiting a wide variety of changes caused by several factors in addition to temperature rises, according to a separate study scheduled for publication in the Journal of Geophysical Research.
That study, authored by scientists from the University of Alaska Fairbanks' Geophysical Institute, reviews records dating back to 1948 for 50 tidewater glaciers in the state but focuses on 36 glaciers and how they changed from 1972 to 2012.
All 36 glaciers experienced significant annual retreat or advance during the period, and 28 of them made significant moves in both ways over those years, the study found.
Twenty-four of the glaciers retreated a total of about 67 miles, 11 advanced a total of almost five miles and one -- Chenega Glacier -- wound up about in the same place as where it started, without a significant change over the period.
There was no "coherent regional behavior signal" that emerged from the data, though there were some patterns in specific locations, the study said.
Factors that were associated with glacier changes, along with temperature, included bedrock geology and presence of marine shoals that serve as barriers protecting some glaciers from relatively warm water, the study said.
Contact Yereth Rosen at yereth(at)alaskadispatch.com.
Correction: An earlier version of this story incorrectly gave discharge figures in square kilometers. It has been updated to cubic kilometers, the correct unit of measurement.