When Jason Gulley steps off the plane Thursday in Ilulissat, Greenland, he’ll be packing rubber waders along with his down parka and cold-weather sleeping bag. The region is experiencing a massive heat wave right now—the same one that hit Europe last week—with some areas expected to top 73 degrees Fahrenheit. This temporary mass of hot air is also turning the frozen surface of the ice sheet that covers the country into patches of slush (spring skiing, anyone?). The meltwater forms rivers and lakes, and then drains into subterranean channels that dive from the surface thousands of feet down to the base of the ice sheet, where it meets bedrock.
As a glaciologist who studies the plumbing system of Greenland’s ice sheet, Gulley is one of the foremost explorers of these melt caves, called moulins. And with the near-record melting this week, the moulins will be roaring like icy waterfalls. “It will be interesting to see how the ice sheet responds to the meltwater inputs,” Gulley said before leaving this week. “We're likely to see a short-lived increase in ice velocity as subglacial water pressure increases.” In plain English, that means the ice sheet will get more slippery this week, like an ice cube sitting on a warm counter. It will slide toward the ocean, where big chunks of it will break off as icebergs.
Gulley, a geoscientist at the University of South Florida, is in Greenland to pick up and bring home 12,000 pounds of scientific monitoring equipment at a remote field camp on the southeastern edge of the ice sheet. He and his colleagues have spent the past three summers on the ice exploring the moulins with remote instruments, using bags of brightly colored tracer dye that they throw into the water and then film using a drone flying overhead. They’ve also pushed the limits by rappelling directly into the caverns to find out where all that meltwater is going. Gulley and an ice climbing specialist, Will Gadd, even trained to dive into one of these meltwater-filled rooms during an expedition sponsored by Red Bull last fall, but the conditions were too dangerous (see their adventures here).
During the past few years, Gulley and his team have found previously unknown reservoirs, like storage tanks for meltwater. He believes these house-size reservoirs act to slow down or speed up the glacier’s movement by regulating how much meltwater reaches the bedrock below. Gulley coauthored a 2014 Nature paper that described Greenland’s unusual drainage system. Since then he has found more of these chambers that help control how fast the entire section of the ice sheet moves, although he and others are still trying to piece together how the whole system works.
“As meltwater happens, it lubricates and allows the ice sheet to move faster,” Gulley said. “But a large amount of water at the top of a glacier doesn’t mean a lot at the bottom.”
Gulley says he doesn't know exactly how many reservoirs there are in the ice sheet or how much meltwater they sop up. Tracking down the whereabouts of the meltwater is important if scientists are to understand how long Greenland’s glaciers will survive the warming planet. At current projections of industrial carbon emissions, melting in Greenland will add more than five feet to global sea level rise over the next 200 years, according to a June study published in the journal Science Advances by researchers at the University of Alaska-Fairbanks and NASA. That five feet means goodbye to most of Florida, New York City, Boston, and a host of other low-lying cities. The study also projected that Greenland’s ice sheet will completely melt in the next 1,000 years unless society drastically reduces carbon emissions and bends the climate curve.
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Understanding how moulins drain ice sheets will allow scientists to better refine their computer models of Greenland’s future, according to Lauren Andrews, a research scientist at NASA’s Goddard Spaceflight Center in Greenbelt, Maryland. “In Greenland we are seeing an increase in surface mass loss over time, and it is accelerating,” Andrews says. “It’s a pretty big ice sheet, but it’s getting smaller.” In addition to warmer air melting the surface of the ice sheet, the edges of the glacial ice sheet are also melting, because underlying ocean temperatures are warmer.
In the early 2000s, scientists studying Greenland thought Greenland’s glaciers and ice sheet were on the brink of a dangerous runaway rapid melting phase known as the Zwally effect, for Jay Zwally, the NASA scientist who published his hypothesis about it. Now, however, Andrews and Gulley both say the ice sheet has some internal checks and balances that prevent that runaway scenario from happening. The speed of the ice sheet movement depends on the slope underneath, for one. And when temperatures drop this fall, that meltwater will freeze inside these moulins, slowing down the lubrication underneath, just like a clogged drainpipe keeps the snow on your roof. The moulins also regulate the water pressure where the ice meets the rock. A higher water pressure lifts the mass of ice slightly and allows the glacier to slip, while lower water pressure keeps it from moving.
Gulley and a colleague will spend a week or so in Greenland this month packing up stream gauges, water pressure sensors, and weather stations at four moulins he’s been studying. In October, Gulley will return to set up a new project to see how many of these reservoirs he can find. This week’s heat wave might break records held since 1950 in Greenland. But in October, when wind-chill temperatures reach 40 below zero, he’ll trade those waders for fur-lined winter boots.