Enlarge / Wolf Point Creek is likely the most-well-studied glacier-fed stream in the world. (credit: Elizabeth via Flickr (CC BY-NC 2.0) )

Pushing off from the dock on a boat called the Capelin , Sandy Milner’s small team of scientists heads north, navigating through patchy fog past a behemoth cruise ship. As the Capelin slows to motor through humpback whale feeding grounds, distant plumes of their exhalations rise from the surface on this calm July morning. Dozens of sea otters dot the water. Lolling on backs, some with babes in arms, they turn their heads curiously as the boat speeds by. Seabirds and seals speckle floating icebergs in this calm stretch of Alaska’s Glacier Bay.

Some two hours later, the craft reaches a rocky beach where Wolf Point Creek meets the sea. The creek is a relatively new feature on the landscape: Land at its mouth first became ice-free in the 1940s due to the melting and retreat of a glacier. It took shape through the 1970s, fed by a mountain lake that slowly formed as an isolated chunk of glacier ice slowly melted. Wolf Point Creek is special because almost its entire life span — from the first, sparse trickles melting out under the ice edge to a mature stream ecosystem teeming with aquatic life, from tiny midge larvae to small fish, and with willows and alder weaving along its edges — is known in intimate detail, its history painstakingly documented.

Milner, a stream ecologist at the University of Birmingham in the UK, has returned almost annually to this spot since the 1970s to catalog how life — particularly aquatic invertebrates — has arrived, thrived and changed over time. He was here to observe meager midges in 1977 and to spot a hundred prospecting pink salmon in 1989. A decade later, his team cataloged 10,000 of the fish spawning in Wolf Point Creek.

Enlarge / Clouds obscure the waters off Greenland's southwest coast. (credit: NASA EO )

While the GRACE satellites were active, their incredibly precise gravity measurements tracked a loss of about 280 billion tons of ice from Greenland each year. That's glacial land ice that raises sea level as it flows into the ocean—and it's vanishing at a remarkable clip. But just how remarkable is that clip? We don't have such excellent measurements going back too far into Greenland's history.

A new study led by the University of Buffalo's Jason Briner takes this question on. We have lots of paleoclimate records of climate conditions in Greenland, the position of the ice on the landscape, and even changes in sediments carried into the sea by meltwater. None of that directly tells you how much ice was accumulating or disappearing. To put the pieces together and calculate that, you need to combine that data with a model.

Digital ice

The researchers used a high-resolution ice-sheet model simulating (roughly) the southwest quadrant of Greenland. There's a good reason for that: the ice sheet mostly melts before reaching the ocean here, making it the simplest area to simulate. Since we've been tracking things, the year-to-year growth or losses of the ice sheet here nicely mirror the Greenland-wide total. So simulate this area well, and at high resolution, and your numbers should scale to the whole ice sheet.

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