Science Torpedoes Reveal How Greenland Is Melting From Below
If the climate keeps warming the way it has, Greenland may finally live up to its name (which was probably bestowed on it by some colorblind viking). The island’s glacier-crusted surface is melting, and a lot of this is from balmier atmospheric temperatures. But as the saying goes, that’s just the tip of the iceberg. The oceans are becoming more tepid as well, and that warmer water is causing the glaciers to thaw from below.
Scientists have good measurements of how much ice melts due to warmer air. And now, thanks in part to torpedo-like probes, they are getting better data on the ice being lapped away by sea water. Those submarines are part of NASA’s Oceans Melting Greenland campaign—OMG, for short. And that’s a fairly accurate acronym, because Oh-My-Goodness those glaciers are melting fast.
“Glaciers acquire mass through snowfall but melt from sun radiation or contact with warm ocean water,” says Michele Koppes, a glacial geomorphologist at the University of British Columbia. Air-induced melting is pretty straightforward. But water makes things a bit more complicated. In Greenland, the melting starts deep. Ocean currents converge off Greenland’s continental shelf. You’d think the warmer water would be near the surface, because it is less dense. But that’s because you didn’t think about salt. Greenland’s warm currents come from the Atlantic Ocean, which is super salty, and therefore denser than the chillier Arctic water.
Greenland’s glacier-gouged coastline provides the deep, warm water a path to the inland ice. Ancient ice sheets carved subsurface fjords and canyons, many of which reach down to the same level as the Atlantic-Arctic currents at the continental shelf. Problem is, “the seafloor around Greenland’s coast isn’t very well known,” says Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory and the project lead for OMG. “The location and depths of these underwater fjords and canyons have just been poorly mapped out.”
Chillin’ with the Bots
Willis and his crew have spent the past five weeks flying over Greenland’s coastline, dropping torpedo-shaped probes into the underwater fjords. These drones are called (deep breath) Glacier and Ice Surface Topography Interferometers (GISTI) with AXCTDS technology, or Airborne Expendable Conductivity, Temperature and Depth Sensors (exhale).
The probes work in teams. One goes deep, measuring saltiness and temperature—essentially, where that warm, deep sea current is. Because it descends at a steady rate, Willis can track its depth by counting how long it’s been in the water. The other stays at the surface, transmitting the deeper probe’s information back to the plane. In the end, the probes will tell the team where ice-ocean interaction is most likely to occur, and how much of the ice sheet is at risk.
Before OMG launched, marine glacial retreat patterns in Greenland had really only been observed by satellites and concentrated fishing surveys. The ship measurements, though, weren’t widespread enough for the research to truly count. And satellite signals mostly bounce off the ocean’s surface.
Mission OMG aims to change this. The program spans five years and will look for ocean-caused changes to Greenland’s ice sheet. This spring, the team measured glacier height with aircraft radar, comparing past and future data to ascertain which glaciers are vanishing the fastest. The subsurface torpedo work took place this fall, when Arctic sea ice was at its minimum. It was the first time underwater probes had collected data on Greenland’s continental shelf depth, salinity and temperature.
Ultimately, the group wants to know how much of Greenland’s melting is because of air temperature, and how much is caused by water. Koppes, who has worked with the OMG team, believes air temperature and ocean water will play a 50/50 role in glacial melting.
Breaking the ice
OMG will need time to analyze the data and confirm, but so far they’ve encountered some surprises. “The amount of warm water was bigger than expected, and we saw it in more places than expected,” continues Willis. “Almost everywhere along the shelf where the water was deep enough, we found Atlantic water interacting with the glaciers.”
And the current isn’t the only deep interaction making the glaciers melt. The Greenland ice sheet is a mile thick, so even when the temperatures at the summit are beyond blustery in the winter (we’re talking -25 °F), the sheet sheathes the cold weather from the bottom of the ice. And where the bottom of the ice makes contact with the bedrock, it’s met with warm temperatures from geothermal heat. Altogether, this thaws out the bottom of the glacier.
And the stakes are high. The deep current warming turns Greenland’s 27,000 miles of coastline—a distance greater than the Earth’s circumference at the equator—into a melt factory. The island’s interior is three times the size of Texas, and holds enough frozen water to raise global sea levels by 20 feet. More than enough to drown the Maldives, Venice, and New Orleans. But hey, maybe those people can resettle in Greenland’s thawed out fjords.
Photo taken from Greenland’s northwestern coastline in September 2015 during Phase 2 of the TerraSond/Cape Race Bathymetry survey.