Archive for the ‘Antarctica’ Category

Glaciers in Antarctica are being melted not only by warmer ocean waters but also by underwater volcanoes, a change in our basic understanding of what’s happening underneath West Antarctica’s ice sheet, scientists say.

Geothermal heat from underneath is helping melt the region’s Thwaites Glacier, in the headlines recently for its rapid melt and retreat, researchers at the University of Texas at Austin say.

Scientists in the university’s Institute for Geophysics say they used ice-penetrating radar aboard aircraft to find significant geothermal heat sources — hotter and spread over a broader area than previously thought — underneath the glacier.

Caused by magma moving underground and volcanic activity associated with that movement, geothermal heat might represent a significant factor in changing the stability of the ice mass above, they researchers reported in the Proceedings of the National Academy of Sciences.

Rather than a uniform region of heat beneath, like a pancake griddle, geothermal sources under the Thwaites Glacier more resemble a stove top with a multitude of burners emitting heat in different locations and at different levels, research scientist Don Blankenship says.

“It’s the most complex thermal environment you might imagine,” he says. “And then you plop the most critical dynamically unstable ice sheet on planet Earth in the middle of this thing, and then you try to model it. It’s virtually impossible.”

The geothermal heat under the glacier averages around 100 milliwatts in each square meter, the researchers said, with some hotspots putting out 200 milliwatts per square meter.

Under the Earth’s other continents the average is less than 65 milliwatts per square meter, they said.

The Thwaites Glacer is an outflow glacier — pushing into the Amundsen Sea — that is the size of Florida and hold the key to trying to predict possible future rises in sea levels, they said.

Studying it could help yield clues to the future state of the entire West Antarctic Ice sheet, they added.

A complete collapse of Thwaites Glacier could push global sea levels up by three to six feet, and a melting of the entire ice sheet could double that, the researchers said.

The combination of warm ocean water and underlying geothermal heat makes the future of the glacier difficult to predict, lead study author Dusty Schroeder says.

“The combination of variable subglacial geothermal heat flow and the interacting subglacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined,” he says.

http://www.techtimes.com/articles/8268/20140610/underground-volcanoes-spur-antartic-glaciar-melt.htm

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Time on his hands. Sebastian Vivancos (inset) is part of the newly arrived team whose planned research activities at the U.S. Palmer Station in Antarctica are being thwarted by the government shutdown.

After 5 years as a lieutenant in the U.S. Coast Guard, Jamie Collins knows what it’s like to be at sea. But nothing in his military service prepared him for his current 30,000-km scientific round trip to nowhere, courtesy of the failure of the U.S. Congress to approve a budget. His predicament is one of the stranger—and sadder—tales of how the government-wide shutdown is affecting researchers.

Collins, a third-year graduate student in chemical oceanography, arrived Wednesday at the National Science Foundation’s (NSF’s) Palmer Station in Antarctica. He was eager to begin working on a long-running ecological research project funded by NSF and to start collecting data for his dissertation in a graduate program run jointly by the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. But the rough seas he encountered during his 4-day crossing of the notorious Drake Passage in the south Atlantic—the final leg of a journey that began in Boston—paled in comparison to the storm he encountered once he stepped off the Laurence M. Gould, a U.S. icebreaking research vessel that ferries scientists and supplies between Puenta Arenas, Chile, and the west Antarctic Peninsula.

On Tuesday, NSF had announced that its contractor for Antarctic logistical support, Lockheed Martin, would begin putting the three U.S. stations on “caretaker” status unless Congress passed an appropriations bill to continue funding the government by 14 October. Although legislators will eventually adopt such a bill, nobody expects them to act in the next few days. Without an appropriation, NSF has no money to operate the stations.

For Collins, that announcement meant his plans for an intensive 5-month research regime had suddenly melted away. “The station manager told us not to unpack our stuff and to stay on the ship,” he says in a phone call to ScienceInsider from the ship. “She said we were to wait here for a week while they prepare to shut down the station. Then we’d sail back to Chile, and go home.”

Collins was stunned. “I had spent all summer preparing for this trip,” he says. He had filled three pallets with supplies for his experiments on how algae in the region detect and react to the presence of ultraviolet radiation, part of a larger effort to understand the role that bacteria play in sequestering carbon in the Southern Ocean. “Without the data from those experiments, I may have to reevaluate what to do for my Ph.D.,” he adds.

Collins was also part of the first wave of students arriving at Palmer this season to work on a research project, begun in 1990, that explores how the extent of annual sea ice affects the polar biota. The project is one of 26 so-called LTER (Long Term Ecological Research) sites around the world that NSF supports. He was scheduled to divide his time at Palmer between his own research and monitoring penguin colonies on several offshore islands as part of the LTER project. And he had signed up for a 6-week research cruise aboard the Gould that supplements the land-based LTER observations with oceanographic data collected up and down the peninsula.

Despite the jarring news, the 31-year-old Collins says that he is more worried about what it may mean to some of his younger colleagues with less worldly experience. “I spent 5 years in the military and I’m used to dealing with bureaucracy,” he explains. “And nothing that happens here is going to deter me from pursuing my goal of a career in science. But for some of the undergraduates on the trip, this is their first taste of what Congress thinks about the value of scientific research. And it’s sending them a pretty horrific message.”

http://news.sciencemag.org/people-events/2013/10/tales-shutdown-grad-student-frozen-out-research-antarctica

Thanks to Dr. Rajadhyaksha for bringing this to the attention of the It’s Interesting community.

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ESA’s CryoSat satellite has found a vast crater in Antarctica’s icy surface. Scientists believe the crater was left behind when a lake lying under about 3 km of ice suddenly drained. Far below the thick ice sheet that covers Antarctica, there are lakes of fresh water without a direct connection to the ocean. These lakes are of great interest to scientists who are trying to understand water transport and ice dynamics beneath the frozen Antarctic surface – but this information is not easy to obtain. About 400 lakes have been discovered at the base of the Antarctic ice sheet. When they drain, they disrupt subglacial habitats and can cause the ice above to slide more quickly into the sea.

One method is to drill holes through kilometres of ice to the water – a difficult endeavour in the harsh conditions of the polar regions.

By combining new measurements acquired by CryoSat with older data from NASA’s ICESat satellite, the team has mapped the large crater left behind by a lake, and even determined the scale of the flood that formed it.

From 2007 to 2008, six cubic kilometres of water – about the same amount that is stored in Scotland’s Loch Ness – drained from the lake, making it the largest event of its kind ever recorded.

That amount of water equals a tenth of the melting that occurs beneath Antarctica each year.

Since the end of 2008, the lake appears to be refilling but six times slower than it drained. It could take decades to reform.

The study, published recently in Geophysical Research Letters, highlights CryoSat’s unique capacity to map changes in Antarctica’s subglacial lakes in 3D, and sheds new light on events at the base of the ice sheet.

CryoSat carries a radar altimeter that can ‘see’ through clouds and in the dark, providing continuous measurements over areas like Antarctica that are prone to bad weather and long periods of darkness.

The radar can measure both the area and depth of ice craters in high resolution, allowing scientists to calculate its volume accurately.

“Thanks to CryoSat, we can now see fine details that were not apparent in older satellite data records,” said Dr Malcolm McMillan from the UK’s University of Leeds and lead author of the study ‘Three-dimensional mapping by CryoSat-2 of subglacial lake volume changes’.

With every subglacial lake, there is hope of finding prehistoric marine life. The rapid draining and apparent refilling of this lake, however, suggests this was not the first time water has drained from the lake.

“It seems likely that the flood water – and any microbes or sediments it contained – has been flushed into the Southern Ocean, making it difficult to imagine that life in this particular lake has evolved in isolation,” said Prof. Andrew Shepherd, a co-author of the study.

http://www.dailygalaxy.com/my_weblog/2013/07/vast-crater-found-under-antarctica-ice-cap.html

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Weddell seals (Leptonychotes weddellii) are the only mammal that dares to swim long distances under sea ice, traveling up to 20 kilometers in hour-long bursts as they scan for air holes and an eventual exit somewhere in the midst of vast Antarctic sheets. There, mothers give birth so that their pups will be safe from leopard seals and killer whales. But how do those pups learn to navigate the risky underwater terrain so quickly? They’re born with big brains, according to a study published online and in an upcoming issue of Marine Mammal Science. Researchers measured 12 carcasses and found that the brains of newborn pups are 70% the size of adult brains—the largest percentage of any mammal. In comparison, the brains of human babies are only 25% the size of adults.

http://news.sciencemag.org/sciencenow/2013/05/scienceshot-big-brains-may-help-.html

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Good news from Antarctica: The hole in the ozone layer is shrinking, new measurements reveal.

Ozone is a molecule made of three oxygen atoms. It’s relatively highly concentrated in a particular layer of the stratosphere about 12 miles to 19 miles (20 to 30 kilometers) above Earth’s surface. This ozone layer prevents ultraviolet light from reaching Earth’s surface — a good thing, given that UV light causes sunburn and skin cancer.

Ever since the early 1980s, though, a hole in this layer has developed over Antarctica during September to November, decreasing ozone concentration by as much as 70 percent. The cause is human-produced chlorofluorocarbons (CFCs), which were once heavily used in aerosols and refrigeration.

By international agreement, CFCs have been phased out of use. The policy has real effects, new satellite observations reveal. In 2012, the hole in the ozone layer over Antarctica was smaller than it has ever been in the last 10 years.

The new observations, announced by the European Space Agency (ESA) on Feb. 8, come from Europe’s Met Op weather satellite, which has an instrument specifically designed to sense ozone concentrations. The findings suggest that the phase-out of CFCs is working, the ESA reports.

Antarctica is particularly vulnerable to ozone-depleting substances, because high winds cause a vortex of cold air to circulate over the continent. In the resulting frigid temperatures, CFCs are especially effective at depleting ozone. The result is that people in the Southern Hemisphere are at increased risk of exposure from UV radiation.

CFCs persist in the atmosphere for a long time, so it may take until the middle of the century for ozone concentrations to rebound to 1960s levels, the ESA reports. However, the hole in the ozone over Antarctica should completely close in the next few decades.

http://www.livescience.com/27049-ozone-hole-shrinks-record-low.html

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The search continues for life in subglacial Lake Whillans, 2,600 feet below the surface of the West Antarctic Ice Sheet—but a thrilling preliminary result has detected signs of life.

At 6:20am on January 28, four people in sterile white Tyvek suits tended to a wench winding cable onto the drill platform. One person knocked frost off the cable as it emerged from the ice borehole a few feet below. The object of their attention finally rose into sight: a gray plastic vessel, as long as a baseball bat, filled with water from Lake Whillans, half a mile below.

The bottle was hurried into a 40-foot cargo container outfitted as a laboratory on skis. Some of the lake water was squirted into bottles of media in order to grow whatever microbes might inhabit the lake. Those cultures could require weeks to produce results. But one test has already produced an interesting preliminary finding. When lake water was viewed under a microscope, cells were seen: their tiny bodies glowed green in response to DNA-sensitive dye. It was the first evidence of life in an Antarctic subglacial lake.

(A Russian team has reported that two types of bacteria were found in water from subglacial Lake Vostok, but DNA sequences matched those of bacteria that are known to live inside kerosene—causing the scientists to conclude that those bacteria came from kerosene drilling fluid used to bore the hole, and not from Lake Vostok itself.)

In order to conclusively demonstrate that Lake Whillans harbors life, the researchers will need to complete more time-consuming experiments showing that the cells actually grow—since dead cells can sometimes show up under a microscope with DNA-sensitive staining. And weeks or months will pass before it is known whether these cells represent known types of microbes, or something never seen before. But a couple of things seem likely. Most of those microbes probably subsist by chewing on rocks. And despite being sealed beneath 2,600 feet of ice, they probably have a steady supply of oxygen.

The oxygen comes from water melting off the base of the ice sheet—maybe a few penny thicknesses of ice per year. “When you melt ice, you’re liberating the air bubbles [trapped in that ice],” says Mark Skidmore, a geomicrobiologist at Montana State University who is part of the Whillans drilling, or WISSARD, project. “That’s 20 percent oxygen,” he says. “It’s being supplied to the bed of the glacier.”

In one possible scenario, lake bacteria could live on commonly occurring pyrite minerals that contain iron and sulfur. The bacteria would obtain energy by using oxygen to essentially “burn” that iron and sulfur (analogous to the way that animals use oxygen to slowly burn sugars and fats). Small amounts of sulfuric acid would seep out as a byproduct; that acid would attack other minerals in the sands and sediments of the lake—leaching out sodium, potassium, calcium, and other materials that would accumulate in the water.

This process, called weathering, breaks down billions of tons of minerals across the Earth’s surface each year. Researchers working on the National Science Foundation-funded WISSARD project hope to learn whether something like this also happens under the massive ice sheets covering Antarctica and Greenland. They’ve already seen one tantalizing sign.

The half mile of glacial ice sitting atop Lake Whillans is quite pure—derived from snow that fell onto Antarctica thousands of years ago. It contains only one-hundredth the level of dissolved minerals that are seen in a clear mountain creek, or in tap water from a typical city. But a sensor lowered down the borehole this week showed that dissolved minerals were far more abundant in the lake itself. “The fact that we see high concentrations is suggestive that there’s some interesting water-rock-microbe interaction that’s going on,” says Andrew Mitchell, a microbial geochemist from Aberystwyth University in the UK who is working this month at Lake Whillans.

Microbes, in other words, might well be munching on minerals under the ice sheet. The Whillans team will take months or years to unravel this picture. They will perform experiments to see whether microbes taken from the lake metabolize iron, sulfur, or other components of minerals. And they will analyze the DNA of those microbes to see whether they’re related to rock-chewing bacteria that are already known to science.

Antarctica isn’t the only place in the solar system where water sits concealed in the dark beneath thick ice. Europa and Enceladus (moons of Jupiter and Saturn, respectively) are also thought to harbor oceans of liquid water. What is learned at Lake Whillans could shed light on how best to look for life in these other places.

http://blogs.discovermagazine.com/crux/2013/01/29/first-evidence-of-life-in-antarctic-subglacial-lake/

Thanks to Kebmodee for bringing this to the attention of the It’s Interesting community.

Handout of an Adelie penguin carrying a video camera on its back stands in Langhovde
An Adelie penguin carrying a video camera on its back stands in Langhovde, Antarctica January 7, 2012, in this handout photo released by Japan’s National Institute of Polar Research’s Assistant Professor Yuuki Watanabe on January 23, 2013. REUTERS/Yuuki Watanabe/National Institute of Polar Research/Handout

Fish of the Antarctic, be very afraid. There’s an unlikely stealth predator on the loose – Adelie penguins.

Forget their ungainly waddling on land or comical bobbing at the ocean’s surface. As soon as these penguins dive into the icy Antarctic ocean, they become calculating, efficient killing machines, say Japanese researchers.

“You could say the penguins have an amazing stealth mode,” said Yuuki Watanabe, a researcher at Japan’s National Institute of Polar Research. “They’re great at sneaking up on their prey and taking them unaware.”

Watanabe this week released footage recorded in December 2010 showing a bird’s eye view of a hunt for fish and small crustaceans called krill, captured using a small video camera strapped to the backs of more than a dozen penguins.

“The krill wiggle their bodies about, they clearly make an attempt to swim off at full speed and escape,” Watanabe said of his findings, published in the U.S.-based Proceedings of the National Academy of Sciences this week.

“But that doesn’t make the slightest difference to the penguins. They just gobble up the krill that are trying to get away and swallow them whole.”

Using the “penguin cams,” which were set to automatically switch on when a penguin entered the water and shoot for 90 minutes, Watanabe and his team were able to capture the secrets of penguins on the hunt.

Additional information came from two accelerometers strapped to each bird that measured its head and body movements to calculate how fast it devoured its prey.

“We didn’t really know if the penguins caught krill one-by-one. I’d thought that maybe they just got into their stomachs when they were after some other prey,” Watanabe said. “But when we saw the footage it turned out the penguins were doing just that, eating these tiny little creatures one after the other.”

Not only that, the penguins didn’t swim randomly but hung poised on the edge of the ice until a thick swarm neared, then swooped into the water. Footage showed a penguin zooming under the ice and then deeper, its head snapping rapidly up as it fed.

The krill killing-rate was both fast and efficient. The penguins gobbled an average of two krill per second when the krill were clustered in swarms, a much faster rate than under general hunting conditions when the penguins consumed about 244 krill in roughly 90 minutes.

“I was so happy when I got the footage of a penguin going straight into a swarm of krill and gorging itself,” Watanabe said.

Penguin research completed, Watanabe now aims to repeat the same exercise with sharks.

http://www.newsdaily.com/stories/bre90n04i-us-japan-penguins-stealth/

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One of the big environmental stories of 2012 was the record melting of sea ice in the Arctic, which reached its smallest extent this summer since satellite data began being kept in the late 1970s. But it’s not the Arctic alone that’s reacting to manmade climate change by transforming into a large puddle. On the other end of the Earth, the continent of Antarctica contains enough ice to swamp just about every coastal city on the planet were it all to melt. The Arctic is transforming before our eyes, but it’s changes in Antarctica that could make Waterworld into a documentary.

That day is still in the distant future—in fact, sea ice in Antarctica has actually increased in recent years, as more powerful northward winds refreeze ice on the continent. But as a new study published in Nature Geoscience shows, temperatures are on the increase in the massive West Antarctica Ice Sheet (WAIS)—and so is melting.

Using data from Byrd Station, a scientific outpost in West Antarctica, researchers from Ohio State University and other institutions have report that average annual temperatures in the region have risen by 2.4 C (4.3 F) since 1958. That’s nearly twice as much warming as had been previously estimated, and the data shows for the first time an increase in warming trends during the summer. The timing of the temperature increase is particularly alarming because while temperatures in Antarctica remain well below freezing for nearly the entire year, the Antarctic summer is when any melting is likely to occur—just as it does in the Arctic.

As lead author David Bromwich put it in a statement:

Our record suggests that continued summer warming in West Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does.

Even without generating significant mass loss directly, surface melting on the WAIS could contribute to sea level indirectly, by weakening the West Antarctic ice shelves that restrain the region’s natural ice flow into the ocean.

Today melting from the WAIS adds only a few millimeters to the ongoing global sea level rise. But there is potential for much, much more—if all the ice in the 10 million sq. mile WAIS were to melt, it would be enough to add 3.05 m (10 ft.) to sea levels. To put that in perspective, all the warming the world has experienced since the Industrial Revolution has cause sea levels to rise by a few inches. That’s scary, world-changing stuff.

http://science.time.com/2012/12/24/antarctica-its-getting-hot-at-the-bottom-of-the-planet/?hpt=hp_t3

Thanks to Ray Gaudette for bringing this to the attention of the It’s Interesting community.

 

Ancient microbes have been discovered in bitter-cold brine beneath 60 feet of Antarctic ice, in permanent darkness and subzero temperatures of Antarctica’s Lake Vida, located in the northernmost of the McMurdo Dry Valleys of East Antarctica.

In the current issue of the Proceedings of the National Academy of Sciences, Nathaniel Ostrom, Michigan State University zoologist, has co-authored “Microbial Life at -13ºC in the Brine of an Ice-Sealed Antarctic Lake.” Ostrom was part of a team that discovered an ancient thriving colony, which is estimated to have been isolated for more than 2,800 years living in a brine of more than 20 percent salinity that has high concentrations of ammonia, nitrogen, sulfur and supersaturated nitrous oxide—the highest ever measured in a natural aquatic environment.”It’s an extreme environment – the thickest lake ice on the planet, and the coldest, most stable cryo-environment on Earth,” Ostrom said. “The discovery of this ecosystem gives us insight into other isolated, frozen environments on Earth, but it also gives us a potential model for life on other icy planets that harbor saline deposits and subsurface oceans, such as Jupiter’s moon Europa.”Members of the 2010 Lake Vida expedition team, Dr. Peter Doran (professor, University of Illinois, Chicago), Dr. Chris Fritsen (research professor, Desert Research Institute, Reno, Nev.) and Jay Kyne (an ice driller) use a sidewinder drill inside a secure, sterile tent on the lake’s surface to collect an ice core and brine existing in a voluminous network of channels 16 meters and more below the lake surface. 

On the Earth’s surface, water fuels life. Plants use photosynthesis to derive energy. In contrast, at thermal vents at the ocean bottom, out of reach of the sun’s rays, chemical energy released by hydrothermal processes supports life. Life in Lake Vida lacks sunlight and oxygen. Its high concentrations of hydrogen gas, nitrate, nitrite and nitrous oxide likely provide the chemical energy used to support this novel and isolated microbial ecosystem. The high concentrations of hydrogen and nitrous oxide gases are likely derived from chemical reactions with the surrounding iron-rich rocks.

Consequently, it is likely that the chemical reactions between the anoxic brine and rock provide a source of energy to fuel microbial metabolism. These processes provide new insights into how life may have developed on Earth and function on other planetary bodies, Ostrom said. The research team comprised scientists from the Desert Research Institute (Reno, Nev.), the University of Illinois-Chicago, NASA, the University of Colorado, the Jet Propulsion Laboratory, Montana State University, the University of Georgia, the University of Tasmania and Indiana University.

For more information: “Microbial life at −13 °C in the brine of an ice-sealed Antarctic lake,” by Alison E. Murray et al. PNAS, 2012. http://www.pnas.org/content/early/2012/11/21/1208607109.abstract Journal reference: Proceedings of the National Academy of Sciences.

http://www.dailygalaxy.com/my_weblog/2012/11/ancient-microbial-life-found-thriving-in-permanent-darkness-60-feet-beneath-antarctica-ice.html

 

The Northern Hemisphere’s largest expanses of ice have thawed faster and more extensively this year than scientists have previously recorded. And the summer isn’t over.

Studies suggest that more of the massive Greenland ice cap has melted than at any time since satellite monitoring began 33 years ago, while the Arctic sea’s ice is shrinking to its smallest size in modern times.

“This year’s melting season is a Goliath,” said geophysicist Marco Tedesco, director of the Cryospheric Processes Laboratory at City University of New York. “The ice is being lost at a very strong pace.”

Scientists monitor the annual thaw closely because changes in the ice of the far North can raise sea levels and affect weather throughout the hemisphere by altering wind currents, heat distribution and precipitation.

Shrinkage of the Arctic sea ice since 2006, for instance, helped lead to seasons of severe snow across Europe, China and North America, researchers at Columbia University, the Georgia Institute of Technology and the Chinese Academy of Sciences reported earlier this year.

As the seasonal ice abates more each year, new polar shipping lanes also open up, as do opportunities for mineral exploration. By some estimates, as much as 25% of the world’s oil and natural-gas reserves are under the Arctic seafloor. Russia, Denmark, Norway and Canada are vying to control these assets.

The giant ice cap at the top of the world partly melts every summer and refreezes every winter. In recent years, the thaw has become progressively more extensive, NASA and European satellite observations suggest. At the same, the refreeze has been smaller—adding up to long-term shrinkage in the ice cover.

This year’s unusual summer thaw was spurred partly by natural variations in weather, but also reflected rising levels of heat-trapping carbon dioxide and methane in the air, amplified by carbon soot from widespread wildfires and the burning of fuels, said scientists at Stanford University and the National Snow and Ice Data Center.

Carried north across the Arctic by winds, soot not only darkens snow and ice, making it absorb more heat from sunlight, but also interferes with the formation of clouds that might otherwise providing cooling shade.

“They all cause enhanced warming in the Arctic,” said Stanford University atmospheric scientist Mark Jacobson, who advocates for renewable energy. “Soot can double the warming.”

In many ways, the Arctic ice pack and Greenland ice cap are mirror opposites. The ice pack is a vast layer of frozen salt water, a few yards thick at most, floating atop an open sea, like ice cubes in a highball. Changes in the size of the Arctic ice can alter weather patterns globally, though the melting doesn’t raise sea levels since the ice displaces the same amount of ocean water when frozen as when liquid.

The Greenland ice sheet is a land-based formation of frozen fresh water up to two miles thick. The water runoff from Greenland ice dilutes the salinity of ocean water, changing its density and altering currents. The runoff that doesn’t refreeze adds to rising ocean levels.

Despite their differences, their fates are linked. “There is little doubt that in terms of warming, things are coming together in the Arctic,” said glaciologist Paul Mayewski, director of the Climate Change Institute at the University of Maine. “Without a doubt, warming in the Arctic is very, very strong,”

In fact, more melting occurred across the Greenland ice cap—the world’s second-largest ice sheet after Antarctica—in June and July than in any year since at least 1979, when satellite monitoring of the island’s ice began, Dr. Tedesco and his colleagues reported earlier this month. The Greenland thaw began in May, a month earlier than usual.

On average, about half of the surface of Greenland’s ice sheet naturally melts during the summer, and then mostly refreezes with the approach of winter. This year, nearly the entire ice cover, from its thin, low-lying coastal edges to its two-mile-thick center, experienced some melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

“This summer, we have seen melting at the very highest elevations of the Greenland ice sheet, which we have not seen before in the satellite record,” said climatologist Thomas Mote of the University of Georgia, who studies snow cover. Researchers expect much of it to refreeze.

By Wednesday, the Arctic sea ice had shrunk to 1.54 million square miles, about 70,000 square miles smaller than the previous modern low set in September 2007, according to the satellite readings compiled by NASA and the National Snow and Ice Data Center in Boulder, Colo. By that measure, the six lowest Arctic sea ice levels on record all occurred in the past six years.

Even when the Arctic ice refreezes, the new ice is often thinner, making it more vulnerable to storms and seasonal temperature variations, said climate scientist Julienne Stroeve at the Snow and Ice Data Center.

About a week remains in the melt season. Researchers won’t know the full extent of this year’s melting until the end of September.

http://online.wsj.com/article/SB10000872396390444772804577621470127844642.html?mod=googlenews_wsj#articleTabs%3Darticle