From #AGU14 Surprising findings in Greenland's melt dynamics – glaciers retreated rapidly between 1900 and 1930

I’m at AGU 2014, thanks to the generous assistance of readers. This is one of the presentations yesterday that caught my eye. One other thing I did notice was that in the poster sessions (which have doubled in size this year) have a lot to say about carbon soot in the Arctic and Southern Greenland as a driver of ice melt. I’ll have more on that later.

San Francisco, California —A combination of new tools and old photographs are giving scientists a better view of Greenland’s ice, and recent discoveries promise to improve forecasts of the region’s future in a warmer world. Overall, the findings show Greenland’s ice is vulnerable to periods of rapid change including vicious cycles of warming promoting further warming.

“In the next century, Greenland melt may raise global sea level by one to three feet,” said Mike MacFerrin, a researcher with CIRES, the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder. “As melting increases in Greenland, we’re discovering that melt water interacts with the ice sheet in unexpected ways. Understanding these mechanisms is crucial to predicting how Greenland’s ice responds to a warming climate, now and in the future.”

MacFerrin spoke during a news briefing at the fall meeting of the American Geophysical Union in San Francisco, California. There, four experts on Greenland highlighted several new findings related to water and ice on the northern island. Some emerged from the discovery and analysis of historic photographs of coastal glaciers; others from hard work dragging ground-penetrating radar across the ice sheet and a series of new imaging techniques innovated during NASA’s Operation IceBridge mission.

The researchers discussed the implications of newly discovered ice layers perched just underneath the surface high on the ice sheet: they likely contributed to damaging coastal floods in 2012 and are poised to contribute more in the future. Firn aquifers, recently found beneath porous snow layers, store substantial amounts of liquid water year round and represent a vast reservoir within the ice. This water contributes to a complex hydrologic system within the ice, both storing and releasing water. And surface lakes that hold liquid water through Greenland’s frigid winters are likely warming the ice sheet, priming it for further melt during summer.

“Many of these discoveries are clears signs of a warming ice sheet,” MacFerrin said. “New tools are allowing us to see these subsurface processes for the first time. If we’re going to understand Greenland’s melt contribution to sea-level rise, we need to understand these new melt features and dynamics.”

Old photos, new insights

Greenland’s glaciers retreated rapidly between 1900 and 1930 as the Little Ice Age lost its grip on the region and temperatures climbed. By analyzing early photos of Greenland paired with contemporary ones, researcher Anders Bjork with the Natural History Museum of Denmark has for the first time mapped out the retreat of those glaciers over time.

“Satellites obviously do not cover the early 1900s, when the region experienced a rapid increase in temperatures,” Bjork said. But with time constraints provided by historic photographs, he and his colleagues recorded a remarkably quick ice response between 1900 and 1930, more rapid than seen in the last 15 years, he said. The new data promise to help researchers understand how quickly glaciers can react to temperature changes, which is important today as the Arctic climate warms again.

Unfrozen

Across wide areas of Greenland researchers are finding, that water can remain liquid, hiding in layers of snow just below the surface, even through cold, harsh winters. The discoveries—made by teams including Rick Forster of the University of Utah and Lora Koenig of the National Snow and Ice Data Center—mean that scientists seeking to understand the future of the Greenland ice sheet need to account for relatively warm liquid water retained in the ice. This discovery also means that the surface hydrologic system, once thought to freeze solid during the winter, can remain active year-round.

Using airborne radars flown during NASA’s Operation IceBridge, Koenig and her colleagues were surprised to see the signature of liquid water under snow. They now report these “buried lakes” are common and extensive on the western margins of the Greenland Ice Sheet. The volume of water retained in buried lakes is small compared with the total mass of water melting from the ice sheet every year, but the lakes can warm the ice and prime the system for melt in spring and summer.

While Koenig was studying persistent “buried lakes” in Western Greenland, Forster was using similar radars and satellite measurements to show extensive water retention in a large aquifer concentrated in southeastern Greenland.

Together these findings present a picture of water remaining just below the surface year round around nearly the entire perimeter of the ice sheet. “More year-round water means more heat is available to warm the ice,” Koenig said. “Simply put, for ice sheet stability, lots of water is not good.”

Ice lenses focus runoff

Two years ago, CIRES graduate student Michael MacFerrin was studying snow compaction on the southwest Greenland ice sheet when their drill hit something completely unexpected: dense layers of ice more than 15 feet thick just under the surface. This high on the ice, the researchers expected to find mostly firn (porous, partially compacted snow) with thin, patchy ice layers or “lenses” scattered within. Such firn acts as a sponge of sorts, soaking up surface meltwater and preventing runoff from high up on the ice sheet.

MacFerrin and his colleagues wondered if the ice layers became thick enough to block surface meltwater, how long might it take for meltwater to pool at the surface and run off toward the coast? Two months later, during the record-breaking melt of July 2012, they got an answer: Landsat 7 satellite images showed unprecedented lakes and rivers forming and draining westward. Meltwater poured into the Watson River 90 miles away, contributing to the worst flooding on record and destroying major portions of a bridge in Kangerlussuaq that had spanned the river for 50 years.

MacFerrin returned to Greenland the following year, armed with the tools needed to survey these ice layers on a larger scale. He and his colleagues dragged a ground-penetrating radar system for over 100 miles behind a snowmobile, and have pored over IceBridge radar data from the ice sheet to find where else in Greenland these thick subsurface layers appear. They now report that continuous, thick ice lenses extend dozens of miles further inland than ever recorded before and cover more than 27,000 square miles, the approximate size of New Jersey, New Hampshire and Vermont combined. Recent record-breaking warm summers (2002, 2005, 2007, 2010, and 2012) appear to have generated large amounts of meltwater, which trickled down, refroze, and fattened once-thin ice layers.

With continued warming in Greenland, more melt water will be generated, adding to the processes recently discovered. “Every few years, the ice sheet surprises us, doing something we never knew it could do,” MacFerrin said. “As melt water expands and feeds all these mechanisms, it’s anybody’s guess what we might discover within the next several years. Using the tools we currently have, we’re doing our best to keep up right now.”

– See more at: http://cires.colorado.edu/news/press/2014/AGUgreenland.html#sthash.LOU3RnlK.8p8jmIi1.dpuf