Hastigheden i Grønlands smeltende ismasser har skiftet gear det seneste årti, så det ikke længere først og fremmest er gletscherne i randen af indlandsisen, der “trækker fødderne til sig”, men store smeltevandssøer inde på selve indlandsisen, der leverer de største vandmasser.
SAN FRANCISCO, 22. December 2014 (Livescience): Greenland’s disappearing ice shifted gears in the past decade, switching from shrinking glaciers to surface melting, researchers reported here last week at the American Geophysical Union’s annual meeting.
Instead of losing ice where massive glaciers meet the sea, Greenland now sends meltwater rushing into the ocean via a vast network of lakes and rivers, according to several studies.
The results do not mean that glaciers have stopped their speedy flow, only that surface melting now exerts a more powerful influence on ice loss, researchers said.
Not so many giant icebergs calving
“We no longer see giant icebergs calving” from glaciers, releasing ice into the sea, said Lora Koenig, a glaciologist at the (US) National Snow and Ice Data Center, who led one of the new studies. “The majority of water is coming from surface melt.”
Koenig discovered that lakes in west Greenland now stay liquid through the frigid winter, as long as an insulating (isolerende) snow blanket keeps the water warm. These lakes get a head start on melting the next summer.
“Water is not a good thing to have persisting year-round,” Koenig said, adding: “What this water is really doing is priming the pump [for melting] for the next season.”
The meltwater boosts sea levels, which are projected to rise by 0.3 to 1.2 meters by 2100, according to the National Climate Assessment.
Water that percolates (siver igennem) beneath the ice sheet can also lubricate (smøre) the underside of Greenland’s glaciers, speeding up ice flow. But researchers are still figuring out where all of this new surface meltwater will end up.
“The water is what we have to follow,” said Vena Chu, a hydrologist and graduate student at the University of California, Los Angeles.
Follow the water
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