OMG, the water's warm! NASA study solves glacier puzzle

June 22, 2018 by Alan Buis, Jet Propulsion Laboratory
Tracy and Heilprin glaciers in northwest Greenland. The two glaciers flow into a fjord that appears black in this image. Credit: NASA

A new NASA study explains why the Tracy and Heilprin glaciers, which flow side by side into Inglefield Gulf in northwest Greenland, are melting at radically different rates.

Using data from NASA's Oceans Melting Greenland (OMG) campaign, the study documents a plume of flowing up Tracy's underwater face, and a much colder plume in front of Heilprin. Scientists have assumed plumes like these exist for glaciers all around Greenland, but this is the first time their effects have been measured.

The finding highlights the critical role of oceans in glacial and their importance for understanding future sea level rise. A paper on the research was published June 21 in the journal Oceanography.

Tracy and Heilprin were first observed by explorers in 1892 and have been measured sporadically ever since. Even though the adjoining glaciers experience the same weather and ocean conditions, Heilprin has retreated upstream less than 2.5 miles (4 kilometers) in 125 years, while Tracy has retreated more than 9.5 miles (15 kilometers). That means Tracy is losing ice almost four times faster than its next-door neighbor.

This is the kind of puzzle OMG was designed to explain. The five-year campaign is quantifying ice loss from all glaciers that drain the Greenland Ice Sheet with an airborne survey of ocean and ice conditions around the entire coastline, collecting data through 2020. OMG is making additional boat-based measurements in areas where the seafloor topography and depths are inadequately known.

About a decade ago, NASA's Operation IceBridge used ice-penetrating radar to document a major difference between the : Tracy is seated on bedrock at a depth of about 2,000 feet (610 meters) below the , while Heilprin extends only 1,100 feet (350 meters) beneath the waves.

This figure shows estimated ice flow velocities of Tracy and Heilprin glaciers (right) and the depths of the fjord in front of the glaciers. The approximate location of the sill in front of Tracy is shown as a dashed yellow line. Research ship cruise tracks are shown in orange. Credit: NASA/JPL-Caltech

Scientists would expect this difference to affect the melt rates, because the top ocean layer around Greenland is colder than the deep , which has traveled north from the midlatitudes in ocean currents. The warm water layer starts about 660 feet (200 meters) down from the surface, and the deeper the water, the warmer it is. Naturally, a deeper glacier would be exposed to more of this warm water than a shallower glacier would.

When OMG Principal Investigator Josh Willis of NASA's Jet Propulsion Laboratory in Pasadena, California, looked for more data to quantify the difference between Tracy and Heilprin, "I couldn't find any previous observations of ocean temperature and salinity in the fjord at all," he said. There was also no map of the seafloor in the gulf.

OMG sent a research boat into the Inglefield Gulf in the summer of 2016 to fill in the data gap. The boat's soundings of ocean temperature and salinity showed a river of meltwater draining out from under Tracy. Because freshwater is more buoyant than the surrounding seawater, as soon as the water escapes from under the glacier, it swirls upward along the glacier's icy face. The turbulent flow pulls in surrounding subsurface water, which is warm for a polar ocean at about 33 degrees Fahrenheit (0.5 degree Celsius). As it gains volume, the plume spreads like smoke rising from a smokestack.

"Most of the melting happens as the water rises up Tracy's face," Willis said. "It eats away at a huge chunk of the glacier."

Heilprin also has a plume, but its shallower depth limits the plume's damage in two ways: the plume has a shorter distance to rise and gathers less seawater; and the shallow seawater it pulls in has a temperature of only about 31 degrees Fahrenheit (minus 0.5 degree Celsius). As a result, even though Heilprin is a bigger glacier and more water drains from underneath it than from Tracy, its plume is smaller and colder.

The study produced another surprise by first mapping a ridge, called a sill, only about 820 feet (250 meters) below the ocean surface in front of Tracy, and then proving that this sill did not keep warm water from the ocean depths away from the glacier. "In fact, quite a lot of warm water comes in from offshore, mixes with the shallower layers and comes over the sill," Willis said. Tracy's destructive is evidence of that.

Explore further: UCI, NASA reveal new details of Greenland ice loss

Related Stories

UCI, NASA reveal new details of Greenland ice loss

February 9, 2017

Less than a year after the first research flight kicked off NASA's Oceans Melting Greenland campaign, data from the new program are providing a dramatic increase in knowledge of how Greenland's ice sheet is melting from below. ...

New Greenland maps show more glaciers at risk

November 1, 2017

New maps of Greenland's coastal seafloor and bedrock beneath its massive ice sheet show that two to four times as many coastal glaciers are at risk of accelerated melting as had previously been thought.

New maps chart Greenland glaciers' melting risk

April 22, 2016

Many large glaciers in Greenland are at greater risk of melting from below than previously thought, according to new maps of the seafloor around Greenland created by an international research team. Like other recent research ...

Study opens window on meltwater from icebergs

December 6, 2017

Surface water conditions in Greenland's fjords and in the northern Atlantic Ocean are dictated by what's going on deep below the surface next to the massive Greenland Ice Sheet, UO-led research has found.

Recommended for you

'Warm' ice in world's highest glacier

November 21, 2018

Ice temperatures inside the world's highest glacier on the slopes of Mount Everest are warmer than expected and especially vulnerable to future climate change, warn glaciologists.

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

leetennant
2.8 / 5 (6) Jun 24, 2018
Sometimes I think there's a great sad irony that the sum of human knowledge will be expanded so much only because we're charting our own extinction.
antigoracle
2.6 / 5 (5) Jun 25, 2018
Sometimes I think ....HEE HAWW....HEE.....HAWW.... we're charting our own extinction.
-- The Chicken Little Jackass brays.

Geothermal springs with homeothermic source water temperature > 2°C (homeothermic springs) can be found all over Greenland but warm springs ≥ 10°C are very rare. They are found primarily in Disko Island, West Greenland....
https://www.geoth...0158.pdf
Thorium Boy
1 / 5 (3) Jun 25, 2018
Wow! A story about something natural without ranting about global warming. What a change.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.