A recently-published study from NASA has revealed that glaciers in West Antarctica’s Marguerite Bay have increased their flow rate, speeding up by up to 25 percent, an event that has accelerated ice loss in the region from 2 to 3 meters (7 to 10 feet) per year to 10 meters (33 feet). Prior to 2008, the flow rates of the four affected glaciers had been stable for two decades, but a major calving event in 1989 left the bay with little to no ice shelf, leaving them with only grounded ice on dry land — a precarious position for its potential to affect sea level rise.
"Grounded ice is a major concern for sea level rise, because it hasn’t contributed to sea level yet," explains JPL’s Catherine Walker, the study’s lead author. "Floating ice has already made its contribution to the sea level." Glaciers that flow into the sea are at risk of increased flow if their sea-borne ice shelves disappear.
The culprit behind the increased flow rate was warmer water entering the region, and although the temperature of the water is only 0.5ºC to 1ºC (1ºF to 2ºF) above normal, this difference was enough to effect the glaciers’ flow rate increase. The influx of warm water was due to a combination of two factors: a moderately strong La Niña event, and the Southern Annular Mode (SAM), a cycle that affects the fluctuation of the band of winds that circumnavigate the Antarctic continent. The La Niña effect caused warmer water to circulate from deep in the ocean up to the surface, while the SAM pushed wind currents farther south, where their temperature was raised by the water, and in turn they warmed the glaciers as the air currents blew over them.
The researchers were surprised at how such a small change in water temperature could cause a larger effect in glacial flow rates. "We detected the warmest water first in January 2009, and by November the glaciers were already losing ice at a rate of eight meters [25 feet] per year in thickness." The acceleration lasted from mid-2008 to 2012, and while the glaciers have slowed since then, their flow rate is still faster than their pre-2008 levels.
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