June 24, 2014
Analyzing The Role Of The Ocean In Greenland Ice Sheet Melting
redOrbit Staff & Wire Reports - Your Universe Online
Ice loss from the Greenland Ice Sheet has increased four-fold over the past four decades, and while warmer atmospheric conditions are to blame for increased melting at the glacier’s surface, scientists now report that oceans play a vital role in how quickly the ice sheet will melt and how much total mass will be lost.According to researchers from the Woods Hole Oceanographic Institution (WHOI) and the University of Oregon, melting of the 1.7-million-square-kilometer, two-mile thick layer of ice covering Greenland has contributed to 25 percent of the world’s sea level rise. Now they have discovered new information about the connection between ocean waters and the country’s outlet glaciers that could alter future estimates of the effects of climate change there.
“Over the past few decades, many glaciers that drain the Greenland Ice Sheet have accelerated, thinned and retreated,” lead author Rebecca Jackson, a graduate student in the MIT-WHOI joint program in oceanography, explained in a statement Sunday.
“Scientists have noticed a link between glacier behavior and warming waters off the coast of Greenland, but we have very few direct measurements of ocean waters near the glaciers or at what time scales they vary, which are needed to understand what’s happening there,” she added.
Scientists believe that the increased rate of ice sheet melting could be the result of warmer waters reaching the underside of the ice in glaciers that extend into the oceans. This phenomenon is called “submarine melting,” but there were few specific details about exactly how it works, as it had not been directly measured at any major Greenland Ice Sheet outlet glaciers, and there was little data about ocean circulation or temperatures in this region.
In the hopes of learning more about the mechanics behind this system, Jackson and her colleagues deployed several moorings in fjords where the third and fifth largest outlet glaciers of the Greenland Ice Sheet terminate. The moorings were deployed between 2009 and 2013. At one site, they were located in the middle of the fjord, in the upper fjord near the glacier, and on the shelf outside the fjord. In the other, a cluster of them were placed in the fjord’s middle.
Using the moorings, the study authors said that they were able to collect extensive temperature and salinity measurements at multiple water depths. In addition, some of them measured ocean currents, providing the first data pertaining to the fjord’s conditions from the period lasting from the fall through the spring. Typically, Jackson explained, data was collected during the summer, when the waters tended to be calmer.
“From their analysis of the data, the researchers found rapid fluctuations in ocean temperature near the glaciers, resulting from ‘surprisingly’ fast ocean currents in the fjords,” WHOI explained. “The fjord currents, which reverse every few days, are driven by winds and ocean currents outside the fjord.”
“These findings imply that changes in temperature in the ocean waters outside the fjord can be rapidly communicated to the glacier, through an efficient pumping of new water into the fjord,” the Institute added. Jackson’s team discovered an unexpected amount of variability in the upper fjord.
That discovery contradicted the widely-held viewpoint that emphasized the induction of freshwater as the source of new water entering fjords, the researchers said. In addition, their observations about ocean property variability in the area around the glaciers indicate the presence of large, rapid fluctuations in submarine melt rates.
Jackson and her associates suspect that the glacier melt rate varies based on the temperature of the water near the ice. Their research was funded by the National Science Foundation and the WHOI Ocean Climate Change Institute, and their findings are detailed in a paper appearing in this week’s edition of the journal Nature Geosciences.