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This is a joint release听of the Cooperative Institute for Research in Environmental Sciences (), the 麻豆免费版下载, and the American Geophysical Union ().

New CU-Boulder-led paper could improve understanding of Greenland鈥檚 contribution to sea level rise

In northwestern Greenland, glaciers flow from the main ice sheet to the ocean in see-sawing seasonal patterns. The ice generally flows faster in the summer than in the winter, and the ends of glaciers, jutting into the ocean, also advance and retreat with the seasons.

A new analysis shows some important connections between these seasonal patterns, sea ice cover and longer-term trends. Glaciologists hope the findings, accepted for publication in the June edition of the American Geophysical Union鈥檚 and available online, will shed light on how a warming Greenland will contribute to sea level rise.

鈥淩ising sea level can be hard on coastal communities, with higher storm surges, greater flooding and saltwater encroachment on fresh water,鈥� said lead author Twila Moon, a researcher at the National Snow and Ice Data Center (NSIDC), part of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the 麻豆免费版下载. 听鈥淲e know that sea level will go up in the future. The challenge is to understand how quickly it will rise, and one element of that is better understanding how Greenland glaciers behave.鈥�

Moon and colleagues from the University of Washington focused on 16 glaciers in northwest Greenland, collecting detailed information on glacier speed, terminus position (the 鈥渆nd鈥� of the glacier in the ocean) and sea ice conditions from 2009 to 2014.

Sea ice had an important influence on the glaciers: When the waters in front of the glacier were completely covered by sea ice, the ends of the glaciers often advanced away from the land; and icebergs - that otherwise might have broken off and floated away - stayed attached. When sea ice broke up in the spring, the ends of the glaciers usually quickly retreated toward land as icebergs broke away.

By contrast, seasonal swings in glacier speed had little to do with sea ice conditions or glacier terminus location. Rather, the speed (or velocity) of ice flow is likely responding to changes in the surface melt on top of the ice sheet and the movement of meltwater through and under the ice sheet.

Over the longer term, however, Moon and her colleagues found a tight relationship between the speed of glaciers and terminus location. When sea ice levels were especially low and glaciers鈥� toes (or termini) retreated more than normal and then didn鈥檛 re-advance, the glaciers sped up, moving ice toward the sea more quickly. While low sea ice is likely not the full cause of the changes, it may be a visible indication of other processes, such as subsurface ice melt, that also affect terminus retreat, Moon said.

It鈥檚 important to recognize that the mechanisms driving seasonal glacier changes in northwestern Greenland and around the world are not necessarily the same ones driving longer-term trends, Moon said. Knowing the differences may help researchers better anticipate the impact of anomalously low sea ice years, for example.

鈥淲e do know we鈥檙e going to see sea ice reduction in this area, and it鈥檚 possible we can begin to estimate how that may affect glacier velocities,鈥� Moon said.

It鈥檚 also possible, she said, that researchers and communities interested in long-term glacial changes鈥攖he kind that affect sea levels鈥攎ay not need to focus as much on seasonal advance and retreat of the rivers of ice.

鈥淚t may be that we need to pay more attention instead to these out-of-bounds events, these anomalous years of very low sea ice or very high melt that likely have the greatest influence on longer-term trends.鈥�

is part of , which is a partnership of听NOAA听and听CU-Boulder.

CIRES contacts:听

• Twila Moon, scientist and lead author NSIDC/CIRES/CU-Boulder (Moon is in Greenland this week, available by email and by Skype)
• Katy Human, CIRES communications, 303-735-0196