格陵兰冰盖下暗藏巨大的蓄水层

Researchers at the University of Utah have discovered a new aquifer（蓄水层） in the Greenland Ice Sheet that holds liquid water all year long in the otherwise perpetually（永恒地） frozen winter landscape. The aquifer is extensive, covering 27,000 square miles. The reservoir is known as a "perennial firn aquifer" because water persists within the firn -- layers of snow and ice that don't melt for at least one season. Researchers believe it figures significantly in understanding the contribution of snowmelt and ice melt to rising sea levels.

The study was published online Sunday, Dec. 22, in the journal Nature Geoscience.

"Of the current sea level rise, the Greenland Ice Sheet is the largest contributor -- and it is melting at record levels," says Rick Forster, lead author and professor of geography at the University of Utah. "So understanding the aquifer's capacity to store water from year to year is important because it fills a major gap in the overall equation of meltwater runoff and sea levels."

Forster's team has been doing research in southeast Greenland since 2010 to measure snowfall accumulation and how it varies from year to year. The area they study covers 14 percent of southeast Greenland yet receives 32 percent of the entire ice sheet's snowfall, but there has been little data gathered.

In 2010, the team drilled core samples in three locations on the ice for analysis. Team members returned in 2011 to approximately the same area, but at lower elevation. Of the four core samples taken then, two came to the surface with liquid water pouring off the drill while the air temperatures were minus 4 degrees Fahrenheit. The water was found at about 33 feet below the surface at the first hole and at 82 feet in the second hole.

"This discovery was a surprise," Forster says. "Although water discharge from streams in winter had been previously reported, and snow temperature data implied small amounts of water, no one had yet reported observing water in the firn（积雪） that had persisted through the winter."

The aquifer is extensive, covering 27,000 square miles -- larger than the state of West Virginia. It is similar in form to a groundwater aquifer on land that can be used for drinking water. "Here instead of the water being stored in the airspace between subsurface rock particles, the water is stored in the air space between the ice particles, like the juice in a snow cone," Forster adds. "The surprising fact is the juice in this snow cone never freezes, even during the dark Greenland winter. Large amounts of snow fall on the surface late in the summer and quickly insulates the water from the subfreezing air temperatures above, allowing the water to persist all year long."