February 3, 2014
Winter Ice Is On The Decline Across Alaskan Lakes
Brett Smith for redOrbit.com - Your Universe Online
According to a new study from the European Space Agency, ice in northern Alaska’s lakes during winter months is on the decline. Twenty years of satellite radar images in the study, which was published in The Cryosphere, show how shifts in our climate are affecting high-latitude regions.
Alterations in air temperature and winter precipitation over the last 50 years have affected the timing, interval and density of the ice cover on lakes in the Arctic, the study said. In this area of Alaska, warmer conditions result in less substantial ice cover on shallow lakes and, as a result, a smaller portion of lakes freeze completely during the winter.
“Prior to starting our analysis, we were expecting to find a decline in ice thickness and grounded ice based on our examination of temperature and precipitation records of the past five decades from the Barrow meteorological station,” said study author Cristina Surdu, a climatologist at the University of Waterloo in Canada.
“At the end of the analysis, when looking at trend analysis results, we were stunned to observe such a dramatic ice decline during a period of only 20 years,” she added.
Using radar imagery from ESA’s ERS-1 and -2 satellites, researchers found a 22 percent drop of ‘grounded ice’ – or ice frozen completely through to the lakebed – from 1991 to 2011. This is equivalent to an overall thinning of ice between 8.2 and 15 inches.
The greatest change was detected from April to May over the course of the 20-year study period. The ice declined most abruptly during the last six years of the investigation, reaching its lowest point in 2011. Radar technology such as those on the ERS mission can pierce through clouds 24 hours a day, delivering constant imagery over areas like northern Alaska that are vulnerable to bad weather and long stretches of darkness. How the radar signals reflect or refract can also be used to figure out if the lake ice was grounded or floating on water.
These transformations in ice cover impact the regional and local climate, the characteristics of the underlying permafrost and the accessibility to water for residential and industrial use during the entire winter. They also modify the physical, thermal and chemical makeup of the water, affecting the ecology reliant on them.
While radar data from these two satellites, in addition to data from the Envisat mission – which concluded in 2012 – allowed sufficient monitoring of freezing lakes, prolonged coverage would strengthen the investigation of ice regimes at high latitudes.
The forthcoming Sentinel-1 mission of the Copernicus program will offer more frequent data collection of this area while providing global continuity of radar imagery for operational lake-ice monitoring.
In December, the ESA revealed that measurements taken by its CryoSat satellite showed the volume of Arctic sea ice has significantly increased this fall, rising by 50 percent compared to last year. Satellites have been showing a downward trend in the area of Arctic Ocean covered by ice over the past few decades, so the latest measurements are much welcomed news, the ESA said.