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Posts Tagged ‘greenland’

Massive Lake of Meltwater Discovered Under Greenland Ice

Posted by feww on December 23, 2013

Researchers discover a meltwater aquifer beneath the southern Greenland ice sheet

The aquifer, representing a previously unknown storage mode for water within the ice sheet, was discovered in 2011, when researchers drilled deep beneath the ice layer and found water flowing back to the surface despite the freezing air temperatures of -15ºC.

The aquifer covers an area of about 70,000 km², an area the size of Ireland, with depth to the top of the water table of 5 to 50m.

The liquid water is held in firn—partially compacted snow—which has the “capacity to store significant amounts of meltwater in liquid or frozen form,” researchers said, “and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet.”

Meltwater from the Greenland ice sheet significantly contributes to the  rise in sea levels. About half of Greenland’s mass loss has been attributed to meltwater runoff.

“Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012,” say the researchers.

A Surprise Discovery

“This discovery was a surprise,” said Prof Rick Forster the lead author from the University of Utah.

“Instead of the water being stored in the air space between subsurface rock particles, the water is stored in the air space between the ice particles, like the juice in a snow cone.”

Scientists are puzzled about the speed, direction and final destination of the meltwater.

“It depends on whether it is currently connected to a system that is draining into the ocean or if it is a bit isolated and completely acting as a storage source without a current connection,” said Forster.

“We don’t know the answer to this right now. It’s massive, it’s a new system we haven’t seen before – we need to understand it more completely if we are to predict sea level rise.”

The research is published in the journal, Nature Geoscience, Published online 22 December 2013.

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Greenland’s Surface Ice Melt

greenland melt extent 2013
An all-time record high temperature for Greenland may have been set in 2013, according to NSIDC.

greenland melt extent 2012-2013 -2
The graph above shows the daily percent of the Greenland Ice Sheet surface that has shown melt, as of August 19, 2013 (red), along with the daily surface melt extent for 2012 (blue) and the average melt extent for 1981 to 2010 (dashed line). Two peak extent days are noted.
Credit: National Snow and Ice Data Center/Thomas Mote, University of GeorgiaHigh-resolution image

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Title: Extensive liquid meltwater storage in firn within the Greenland ice sheet
Authors: Richard R. Forster et al.
Abstract:

Mass loss from the Greenland ice sheet contributes significantly to present sea level rise. High meltwater runoff is responsible for half of Greenland’s mass loss. Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012. However, how surface melt water reaches the ocean, and how fast it does so, is poorly understood. Firn—partially compacted snow from previous years—potentially has the capacity to store significant amounts of melt water in liquid or frozen form, and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet. We find a substantial amount of water in this firn aquifer that persists throughout the winter, when snow accumulation and melt rates are high. This represents a previously unknown storage mode for water within the ice sheet. We estimate, using a regional climate model, aquifer area at about 70,000km2 and the depth to the top of the water table as 5–50m. The perennial firn aquifer could be important for estimates of ice sheet mass and energy budget.

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Greenland Ice Sheet Losing Ice Mass

Posted by feww on March 24, 2010

Greenland Ice Sheet Losing Ice Mass on Northwest Coast: International Study

Greenland ice sheet lost about 1,604 km³ (385 cubic miles) of ice between April 2002 and February 2009, an amount equivalent to about 0.5 mm of sea-level rise each year, researchers say.

Greenland ice sheet has been losing an increasing amount of ice since 2000. Previously most of the loss was concentrated in its southern region, but now the loss is occurring in its northwest coast, a new international study says.


Click image to enlarge.


Greenland Melt Extent, 2005: Konrad Steffen and Russell Huff – Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder

Researchers from Denmark Technical Institute’s National Space Institute in Copenhagen and the University of Colorado at Boulder say the ice-loss acceleration started moving up the northwest coast of Greenland in late 2005. “The team drew their conclusions by comparing data from NASA’s Gravity and Recovery Climate Experiment satellite system, or GRACE, with continuous GPS measurements made from long-term sites on bedrock on the edges of the ice sheet.”

The uplift rates of about 4 centimeters  were discovered close to the Thule Air Base on Greenland’s northwest coast between October 2005 to August 2009. “Although the low resolution of GRACE—a swath of about 155 miles, or 250 kilometers across—is not precise enough to pinpoint the source of the ice loss, the fact that the ice sheet is losing mass nearer to the ice sheet margins suggests the flows of Greenland outlet glaciers there are increasing in velocity, said the study authors.” The report said

“When we look at the monthly values from GRACE, the ice mass loss has been very dramatic along the northwest coast of Greenland,” said CU-Boulder physics Professor and study co-author John Wahr, also a fellow at CU-Boulder’s Cooperative Institute for Research in Environmental Sciences.

“This is a phenomenon that was undocumented before this study,” said Wahr. “Our speculation is that some of the big glaciers in this region are sliding downhill faster and dumping more ice in the ocean.”

“These changes on the Greenland ice sheet are happening fast, and we are definitely losing more ice mass than we had anticipated, ” said Isabella Velicogna of the University of California-Irvine, who also is a scientist at NASA’s Jet Propulsion Laboratory. “We also are seeing this ice mass loss trend in Antarctica, a sign that warming temperatures really are having an effect on ice in Earth’s cold regions.”

Click here for the rest of the report and a computer simulation of Greenland Ice Melt.

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Posted in Ice Mass, ice-loss, ice-loss acceleration, polar ice, sea level rise | Tagged: , , , , | 1 Comment »

Ice Melt in Alaska, Antarctica, Greenland Accelerating

Posted by feww on December 17, 2008

2 trillion tons of ice in Alaska, Antarctica and Greenland melted since 2003, NASA says

About 2 trillion tons of ice in Alaska, Antarctica  and Greenland has melted since 2003,  NASA scientists say, due to accelerating climate change.

Analyzing data from NASA’s Gravity Recovery and Climate Experiment, GRACE, in which two orbiting satellites are used to measure the “mass balance” of a glacier, that is the net difference between ice accumulation and ice loss each year, NASA geophysicist Scott Luthcke says the losses are colossal.

“The ice tells us in a very real way how the climate is changing,” said Luthcke. “A few degrees of change [in temperature] can increase the amount of mass loss, and that contributes to sea level rise and changes in ocean current.”

Greenland has lost about 160 gigatons (one billion tons) each year for 5 consecutive years, enough to raise global sea levels about .5 mm per year,  according to another NASA researcher, Jay Zwally.

“Every few extra inches of sea level have very significant economic impacts, because they change the sea level, increase flooding and storm damage,” said Zwally. “It’s a warning sign.”

“We’re seeing the impacts of global warming in many areas of our own lives, like agriculture,” he said.

Citing the pine beetle infestation in the forests of Colorado and western Canada [how about Alaska?] he said: “[The pests] were believed to be spreading because the winter was not cold enough to kill them, and that’s destroying forests.”

Sermersuaq (Humboldt) Glacier, Greenland


acquired August 30, 2008 – NASA Earth Observatory


acquired August 30, 2000 – NASA Earth Observatory

Stretching about 90 kilometers across Kane Bassin in the Nares Strait, northwestern Greenland’s Sermersuaq Glacier, also called Humboldt Glacier, is the Northern Hemisphere’s widest tidewater glacier—a glacier that begins on land, but terminates in water. The Sermersuaq is a major source of icebergs in the strait, which connects the Lincoln Sea in the north to Baffin Bay in the south.

This pair of images shows the retreat of the Sermersuaq Glacier between 2000 and 2008. In these natural-color images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, the approximate terminus of the glacier on August 31, 2000 (bottom image), is traced with a yellow line on an image from August 30, 2008 (top). Although the southern part of the terminus showed little change during the period, significant retreat is visible in the northern part, where a fast-flowing ice stream is located. In both images, the deep blue waters of Kane Bassin are littered with ice, which may include icebergs and sea ice.

Having a “toe” in the water adds complexity to the natural cycle of advance and retreat that a glacier experiences in response to climate changes. The behavior of tidewater glaciers is affected not only by melting and snowfall on land, but also by the shape of the fjord or coastline where the glacier enters the water, the depth of the water, tides, and the thickness of the moraine (a shoal of sediment and rock) that builds up underwater at the tip of the glacier.

Even in the absence of human-caused climate change, tidewater glaciers naturally experience century-long cycles that include phases of rapid retreat. After decades of slow advance, the terminus of the glacier eventually becomes grounded on its own moraine. The shoal can become so thick that it stops icebergs from calving for extended spans of time. The support of the shoal allows the glacier to grow larger than it could if it were free-floating.

A small amount of thinning or retreat at the terminus can trigger a rapid retreat once the glacier—too large to float—is ungrounded from the shoal. The initial thinning or retreat of a tidewater glacier may result from a warming climate, but the extremely rapid retreat thereafter has as much to do with topography and the laws of physics as it does with the current climate.

NASA image created by Jesse Allen, using data obtained from the Goddard Level 1 and Atmospheric Archive and Distribution System (LAADS). Caption by Rebecca Lindsey.

Instrument: Terra – MODIS
Date Acquired: August 30, 2008

Posted in Colorado forests, pine beetle infestation, Sermersuaq Glacier, western Canada | Tagged: , , , , | 3 Comments »

Sea Surface Height Variations

Posted by feww on July 2, 2008

From NASA’s Earth Observatory

Regional Patterns of Sea Level Change 1993-2007

globalssh_jsn_2007

Unlike the water in a sink or a bathtub, the water level in Earth’s oceans is not the same everywhere; sea level varies with location and time. On time spans of hours to days, sea level is influenced by tides, winds, and waves, including storm surges. Sea level rises when oceans warm, and it drops when they cool (because water expands when it heats up and contracts when it cools). Regional variations in sea level can persist for many years, even a decade. Underlying all these changes is the slower rise and fall in global average sea level as ice ages recede and advance over millenia.

This map shows global patterns of changes in sea level (sea surface height) measured by satellite-based altimeters (Topex and Jason 1 satellites) from 1993 through the end of 2007. Places where the sea surface height increased up to 225 millimeters (about 8.9 inches) are shown in dark red; places where sea level dropped are blue. The most widespread change in sea level over this time period was an increase in the Western Pacific sea surface height. During the period spanned by this image, a climate pattern called the Pacific Decadal Oscillation was in its warm phase, and sea surface temperatures were above average in much of the basin. Thermal expansion during this warm phase would be consistent with a rise in sea level.

Other changes reflect shifts in large-scale ocean currents. For example, the sea level rose in the North Atlantic Ocean south of Greenland. The rise is related to a weakening of an ocean current known as the North Atlantic Subpolar Gyre. The subpolar gyre is a counter-clockwise current in the North Atlantic whose descending branch flows southward along the southeast coast of Greenland. When the gyre is strong, it carries cold, salty water deep into the ocean, where it flows back toward the equator. When the current weakens, temperatures warm and sea level rises.

Other areas in the image that suggest a decadal-scale change in ocean currents include the mid-Atlantic off the east coast of the United States, where the line of blue (drop in sea level) could indicate a change in the average latitude or velocity of the Gulf Stream Current. A sea level rise occurred in the area of the western Pacific east of Japan that is influenced by the Kuroshio Current, which is the analogue of North America’s Gulf Stream. Finally, a scattering of dark red dots across the Southern Ocean between Africa and Australia may signify a change in the Antarctic Circumpolar Current.

Full article including references is available at: Regional Patterns of Sea Level Change 1993-2007

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Arctic Melting FAST!

Posted by feww on April 24, 2008

Rocket Science: Ice + Heat = Water


Arctic summer sea ice. Image taken by NASA satellite September 16, 2007.

News Reports:

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Vanishing Lakes

Posted by feww on April 18, 2008

Source: Media Relations

Researchers from the Woods Hole Oceanographic Institution (WHOI) and the University of Washington (UW) have for the first time documented the sudden and complete drainage of a lake of meltwater from the top of the Greenland ice sheet to its base.

From those observations, scientists have uncovered a plumbing system for the ice sheet, where meltwater can penetrate thick, cold ice and accelerate some of the large-scale summer movements of the ice sheet.

According to research by glaciologists Sarah Das of WHOI and Ian Joughin of UW, the lubricating effect of the meltwater can accelerate ice flow 50- to 100 percent in some of the broad, slow-moving areas of the ice sheet.


WHOI glaciologist Sarah Das stands in front of a block of ice that was raised up 6 meters by the sudden drainage of a meltwater lake in Greenland. (Photo by Ian Joughin, UW Polar Science Center)” Image may be copyrighted. See FEWW Fair Use Notice!

“We found clear evidence that supraglacial lakes—the pools of meltwater that form on the surface in summer—can actually drive a crack through the ice sheet in a process called hydrofracture,” said Das, an assistant scientist in the WHOI Department of Geology and Geophysics. “If there is a crack or defect in the surface that is large enough, and a sufficient reservoir of water to keep that crack filled, it can create a conduit all the way down to the bed of the ice sheet.”

But the results from Das and Joughin also show that while surface melt plays a significant role in overall ice sheet dynamics, it has a more subdued influence on the fast-moving outlet glaciers (which discharge ice to the ocean) than has frequently been hypothesized. (To learn more about this result, read the corresponding news release from UW.)

The research by Das and Joughin was compiled into two complementary papers and published on April 17 in the online journal Science Express. The papers will be printed in Science magazine on May 9. Full press release Copyright ©2007 Woods Hole Oceanographic Institution, All Rights Reserved.

Posted in geology, Geophysics, glaciers, hydrofracture, Oceanography | Tagged: , , , , , , , , | 1 Comment »