EcoAlert: “Greenland’s Great Melt” –NASA Monitoring the Massive Ice Sheet That’s Adding 250 Gigatonnes of Water to Ocean Per Year (WATCH Today’s ‘Galaxy’ Stream)

 

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Global sea level rise will be one of the major environmental challenges of the 21st Century. NASA' s Oceans Melting Greenland (OMG) a 5-year airborne and ship-based mission that will pave the way for improved estimates of sea level rise by addressing the question: To what extent are the oceans melting Greenland’s ice from below?

NASA is keeping a watchful eye on Greenland, tracking changes in the thick sheet of ice that covers most of the island. Why? Well for the same reason that coal miners used to bring canaries into the coal mines. If they stopped singing, it was a warning sign that trouble was coming.

Greenland's ice sheet is one of Earth's canaries when it comes to global warming. Polar regions are more sensitive to a warming Earth than other parts of the world. So what happens in places like Greenland, the rest of the Arctic, and Antarctica, alerts us to what’s in store for the rest of the planet.

NASA is keeping a watchful eye on Greenland, tracking changes in the thick sheet of ice that covers most of the island. Why? Well for the same reason that coal miners used to bring canaries into the coal mines. If they stopped singing, it was a warning sign that trouble was coming.

 

 

Greenland's ice sheet is one of Earth's canaries when it comes to global warming. Polar regions are more sensitive to a warming Earth than other parts of the world. So what happens in places like Greenland, the rest of the Arctic, and Antarctica, alerts us to what’s in store for the rest of the planet.

And Greenland’s ice can also affect many of us directly. You see, Greenland has more land ice than any other place except Antarctica. If it all melted, it would raise sea level around twenty-three feet. That’s enough to put coastlines throughout the world under water. And in fact, the ice is melting. It’s far from all gone — that could take centuries. But Greenland’s ice sheet currently adds about 250 gigatonnes of water to the ocean every year. That's a billion ton, which is approximately a block of ice one kilometer square. And 250 of these giant Greenland ice blocks melt every year.

With temperatures around the world climbing, melt waters from the continental ice sheets of Greenland and Antarctica are raising sea levels. Those ice sheets are melting from both above and below. Much of the ice lost from ice sheets comes from a process called calving where ice erodes, breaks off, and flows rapidly into the ocean. A large volume of ice is also lost from ice sheets melting on their surfaces.

Previous research has shown that Greenland's glaciers, which flow like rivers of ice into the ocean, sit on the ground deeper below sea level than had been thought. Warm ocean currents sweep across and erode the hidden glacier faces. As a result, they’re melting faster – a few feet a day in summer – than anyone suspected.

The diagram above represents a typical glacier in Greenland. Below the cold, fresh layer near the surface a layer of warm, salty water reaches into the fjords to melt the glacier's edge. OMG will measure the volume and extent of this warm layer each year and relate it to thinning and retreat of the glaciers.

OMG will use NASA’s G-III to fly the Glacier and Ice Surface Topography Interferometer (GLISTIN-A) in order to generate high resolution, high precision elevation measurements of Greenland’s coastal glaciers during the spring. Annual surveys by GLISTIN will measure glacier thinning and retreat over the preceding season. A second aircraft campaign, also on the NASA G-III, will be occur each year in the summer to deploy 250 expendable temperature and salinity probes along the continental shelf to measure the volume, extent, of warm, salty Atlantic Water. These data, along with fundamental new and critical observations of airborne marine gravity and ship-based observations of the sea floor geometry will provide a revolutionary data set for modeling ocean/ice interactions and lead to improved estimates of global sea level rise.

Oceanographer Josh Willis is the Principal Investigator for the OMG mission. He says, “We’re investigating how the ice interacts with the ocean, and how much the oceans are melting away the glaciers from the edges of the ice sheet.”

For this study, a NASA aircraft is flying the Glacier and Ice Surface Topography Interferometer (GLISTIN) instrument around Greenland for a few weeks each year.

Willis says, “GLISTIN is making very high resolution maps of the ice, showing us how fast the glaciers are thinning and retreating right at the edge.”

The aircraft will also continue dropping more than 200 ocean probes each year through 2020 to measure how temperature and salinity change between the ocean surface and the sea floor – from the cold meltwater at the surface down to the warmer, heavier saltwater below. This will help determine how changes in the ocean affect the ice.

In addition, OMG has completed surveys using a ship equipped with sonar to measure the seafloor shape and depth, which affect where and how much the warm water from the Atlantic eats away at the coastal glaciers. The mission also conducted airborne measurements of gravity off the coast of Greenland, giving the team more information about the depth of water in those locations.

While OMG is looking at the effects on ice sheets from below, NASA’s Operation IceBridge mission is surveying polar ice from above. The overlap of OMG and IceBridge is providing the most accurate measurements to date of changes in Greenland’s ice sheet mass.

Glaciologist Ala Khazendar, a member of the OMG science team says, “IceBridge's highly-accurate Airborne Topographic Mapper is the gold standard of measuring the surface elevation changes of the ice sheet. With OMG uncovering how much ice is being lost at the periphery of the ice sheet, and IceBridge telling us how the thickness of the glaciers is changing further upstream, we can better attribute Greenland’s ice loss either to changes in the ocean or warming of the atmosphere, which directly melts the ice from above.”

“Greenland contains enough ice to raise global sea levels by 20 feet (6 meters) if it all melted,” notes Willis. “Right now we think this will take at least several hundred years, but data from OMG are helping scientists better understand how much the oceans are melting Greenland’s ice. From now through 2020, OMG will be making annual visits to measure the oceans and ice together, helping scientists study changes to Greenland’s ice sheet and how those changes may impact Earth’s environment.

The Daily Galaxy via NASA OMG and science.nasa.gov.

 

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