Home / Science / While Greenland melts, where is the water?

While Greenland melts, where is the water?











In the vast ice sheet of Greenland, meltwater flows in streams, as sunlight and hot air heat the ice on the surface.


Surface variations create thousands of low areas where melt water accumulates and eventually drains.


Streams drain into larger rivers that carve natural roads through the ice sheet.


Over the years, the impurities in the ice are concentrated, making it darker. Those areas absorb more sunlight, causing more melting.


Below the surface, the ice develops holes, like Swiss cheese.


This river reached a great depression in the ice and formed a lake.


The lake fed another fast-moving river on the opposite side.


That river disappeared through a hole in the ice, called moulin.


Sea level rise depends on the amount of water draining from the ice sheet into the ocean and the velocity.


New research suggests that more water can get trapped inside the ice sheet than previously thought.

In the vast ice sheet of Greenland, meltwater flows in streams when sunlight and hot air heat the surface of the ice.

Surface variations create thousands of low areas where melt water accumulates and drains.

Streams drain larger rivers that carve natural roads through the ice sheet.

Over the years, the impurities in the ice are concentrated, which makes it darker. These areas absorb more heat and cause greater fusion.

This river reached a depression in the ice and formed a lake, which fed another river on the opposite side.

That river disappeared through a hole in the ice, called moulin.

Sea level rise depends on the amount of water draining from the ice sheet into the ocean. New research suggests there may be more water trapped in the ice than previously thought.

In the summer of 2015, two journalists from the New York Times joined a team of researchers in Greenland that was conducting a unique experiment: directly measuring a river of meltwater runoff on the top of the ice.

Now, scientists published the results of that work. A key finding – that not so much meltwater flows immediately through the ice sheet and drains into the ocean as previously estimated – may have implications for sea level rise, one of the main effects of climate change.

Scientists say it appears that some of the fusion water is retained in porous ice instead of flowing to the bottom of the ice sheet and into the sea.

"It's always treated like a parking lot, the water runs directly," said Laurence C. Smith, a geographer at the University of California, Los Angeles, who led the fieldwork in 2015. "What we found is that it seems that there is water retention. "

"It is plausible that this is a very important process, that the level projections could be too high," he added.








Much remains to be discovered about the ice sheet, which at approximately 650,000 square miles is more than twice the size of Texas. The blade, up to two miles thick, contains enough ice that, if everything melted, would lift the oceans around the world by 24 feet. Precisely how the ice melts – half or more when heated on the surface, the rest by the movement of the ice sheet to the sea, where it melts or tenderizes like icebergs – can greatly affect the speed at which they rise the seas.

Greenland is currently losing an average of approximately 260 billion tons of ice per year; at this rate, it would contribute approximately two inches to the rise in sea level by the end of the century. This loss of ice is estimated through gravity measurements by satellites, but computer models that simulate physical processes are used to estimate surface runoff. The field study aimed to improve these models by providing field data on the melt water flow.





Change in the mass of the Greenland ice sheet

since 2002, in billions of metric tons

-1,000 million [19659028] metric tons

Change in the mass of Greenland Ice [19659026] since 2002, in billions of metric tons

-1,000 million

metric tons

Change in the mass of Greenland Ice

since 2002, in billions of metric tons




The work consisted of establishing a camp near a glacial river that drains the meltwater from a surrounding catchment area, in this case about 24 square miles of the ice sheet, into a mill, a hole that drains to the base of The ice sheet The researchers suspended a device in the river that uses acoustic signals to measure the flow and used satellite and drone images to calculate accurately the catchment area.

Flow data collected over 72 hours showed that current models overestimate the amount of runoff by 20 percent to almost 60 percent. The models were wrong? Or were they right about the total amount of fusion, but some of the water was not leaking?

When he first sent the results to the modelers, Dr. Smith said, "they could not believe it." After months of back and forth, Dr. Smith and his colleagues concluded that the model estimates were accurate, but there was something else at stake with some of the meltwater. "What is missing," he said, "is a physical process that is currently not considered by the models: ice water retention."

Sunlight hitting the ice sheet melts the surface, said Dr. Smith, but some of the light penetrates deeper into the ice and causes it to melt there. The ice develops a porous and rotten texture, and may, the findings suggest, cling to part of the meltwater.





Display area

at the top of this article

Display area

at the top of the article




The New York Times | Source: DigitalGlobe satellite images through Laurence Smith at the University of California, Los Angeles

Marco Tedesco, co-author of a work on the Proceedings of the National Academy of Sciences modeling at Lamont-Doherty Earth Observatory, Part of Columbia University said that when comparing models with real field measurements, "the energy involved is always observed."

"If there is a mismatch between the observation and the model," said Dr. Tedesco, "that means that the model is moving the mass one way or another and not respecting the way things happen in the real world. "

Additional work on the ice sheet will try to measure directly how much water is retained in the ice. More direct flow measurements are also needed, since conditions can vary greatly in the huge ice cap. (As the original Times article revealed, measuring the flow of an ice sheet is much more complicated and dangerous than doing it on land.)

But surface runoff is just one area where much remains to be learned. What happens at the bottom of the ice when the melting water reaches it is largely understood through modeling, and those processes can affect the speed with which the ice sheet moves and, therefore, the amount of ice that descends to the ocean.

the study is bioalbedo, which is how the growth of microorganisms in ice can darken the surface and affect the rate at which it melts.

Thomas P. Wagner, a NASA program scientist who directs the agency's efforts to study the polar regions, said studies like Dr. Smith's – and much larger research on the Antarctic ice sheet – They are fundamental to understand how climate change will affect the globe.

"Sea level increases 3 millimeters a year at this time," said Dr. Wagner. "But in a hundred years, we could be one to five feet tall."

"Every day we are improving our understanding of how ice is getting into the ocean," he added. "The general context is that we are in this"


Source link

Leave a Reply

Your email address will not be published. Required fields are marked *