Runaway Glacier melt in West Antarctica Ice

The leading edge of the floating ice tongue of the Pine Island Glacier, Antarctica. 

Credit: M. Wolovick

Reports that a portion of the West Antarctic Ice Sheet (WAIS) has begun to irretrievably collapse, threatening a 4-foot rise in sea levels over the next couple of centuries, surged through the news media last week.

But many are asking if even this dramatic news will alter the policy conversation over what to do about climate change.

West Antarctic Ice Sheet (WAIS)

Glaciers like the ones that were the focus of two new studies move at, well, a glacial pace. Researchers are used to contemplating changes that happen over many thousands of years.

This time, however, we're talking hundreds of years, perhaps—something that can be understood in comparison to recent history, a timescale of several human generations.

In that time, the papers' authors suggest, melting ice could raise sea levels enough to inundate or at least threaten the shorelines where tens of millions of people live.

"The high-resolution records that we're getting and the high-resolution models we're able to make now are sort of moving the questions a little bit closer into human, understandable time frames," said Kirsty Tinto, a researcher from Lamont-Doherty Earth Observatory who has spent a decade studying the Antarctic.

"We're still not saying things are going to happen this year or next year. But it's easier to grasp [a couple of hundred years] than the time scales we're used to looking at."

The authors of two papers published last week looked at a set of glaciers that slide down into the Amundsen Sea from a huge ice sheet in West Antarctica, which researchers for years have suspected may be nearing an "unstable" state that would lead to its collapse.

The West Antarctic Ice Sheet (WAIS) is mostly grounded on land that is below sea level (the much larger ice sheet covering East Antarctica sits mostly on land above sea level).

Advances in radar and other scanning technologies have allowed researchers to build a detailed picture of the topography underlying these glaciers, and to better understand the dynamics of how the ice behaves.

Where the forward, bottom edge of the ice meets the land is called the grounding line. Friction between the ice and the land holds back the glacier, slowing its progress to the ocean.

Beyond that line, however, the ice floats on the sea surface, where it is exposed to warmer ocean water that melts and thins these shelves of ice.

As the ice shelves thin and lose mass, they have less ability to hold back the glacier.

What researchers are finding now is that some of these enormous glaciers have become unhinged from the land – ice has melted back from earlier grounding lines and into deeper basins, losing its anchor on the bottom, exposing more ice to the warmer ocean water and accelerating the melting.

The glaciers studied by Eric Rignot’s research team. 

Red indicates areas where flow speeds have increased over the past 40 years. 

The darker the colour, the greater the increase. 

The increases in flow speeds extend hundreds of miles inland. 

Credit: Eric Rignot.

In their paper published in Geophysical Research Letters, Eric Rignot and colleagues from the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, Calif., described the "rapid retreat" of several major glaciers over the past two decades, including the Pine Island, Thwaites, Haynes, Smith and Kohler glaciers.

"We find no major bed obstacle upstream of the 2011 grounding lines that would prevent further retreat of the grounding lines farther south," they write.

"We conclude that this sector of West Antarctica is undergoing a marine ice sheet instability that will significantly contribute to sea level rise in decades to come."

More information: Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith and Kohler glaciers, West Antarctica from 1992 to 2011, E. Rignot, J. Mouginot, M. Morlighem, H. Seroussi, B. Scheuchl, Geophysical Research Letters (2014)

Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica, Ian Joughin, Benjamin E. Smith, Brooke Medley, Science (2014)

NASA and NOAA help reveal melt secrets of Great Lakes ice

A colour-coded image of major ice types on Lake Superior, made from a RADARSAT1 radar backscatter image using a new NASA and NOAA-developed technique. 

Credit: NOAA Great Lakes Environmental Research Laboratory and NASA/JPL-Caltech

Two scientists from NASA and NOAA have developed a new space-based technique for monitoring the ice cover of the Great Lakes that is so accurate it can identify a narrow channel of open water cut through the ice by an icebreaker—even at night.

"In the dark, it's difficult to read a map that's right in front of you," said Son Nghiem of NASA's Jet Propulsion Laboratory, Pasadena, Calif., one of the developers of the new technique.

Son Nghiem

"Yet we now have a way to use satellite radars almost 500 miles [800 kilometers] out in space to see through clouds and darkness and map ice across the Great Lakes."

Ice on the Great Lakes puts a big chill on the U.S. and Canadian economies, affecting shipping, fishing and also public safety when winter and spring flooding are caused by ice jams.

It has a significant impact on the regional environment and ecological systems as well. Yet previous techniques of analyzing satellite observations of the ice sometimes misidentified ice as water and vice versa.

The new method, co-developed by Nghiem and his colleague George Leshkevich of NOAA's Great Lakes Environmental Research Laboratory, Ann Arbor, Mich., not only corrects that problem, it also gives a more accurate analysis of ice characteristics, such as whether the ice is dense or full of bubbles, and whether it has melted and refrozen.

Leshkevich said the method has now been transitioned to NOAA for routine use in generating ice maps across the Great Lakes.

"These maps will provide important information for environmental management, ice forecasting and modeling, off-shore wind farm development, operational icebreaking activities in support of winter navigation, and science research."

The more accurate classification of ice will also be useful for scientific research into such questions as how the Great Lakes are responding to, and leading, climate change in the upper Midwest.

More information: www.iaglr.org/jglr/release/39/2013.05.003_leshkevich.php

Mineral analysis of Copernicus lunar crater deposit - Melted rock

Pre-existing mineral deposits on the Moon (sinuous melt, above) survived impacts powerful enough to melt rock. 

Visible only in certain wavelengths, the deposits are not detectable in the crater image (inset). Large impacts on the Moon can form wide craters and turn surface rock liquid.

Geophysicists once assumed that liquid rock would be homogenous when it cooled. Now researchers have found evidence that pre-existing mineralogy can survive impact melt.

Despite the unimaginable energy produced during large impacts on the Moon, those impacts may not wipe the mineralogical slate clean, according to new research led by Brown University geoscientists.

The researchers have discovered a rock body with a distinct mineralogy snaking for 18 miles across the floor of Copernicus crater, a 60-mile-wide hole on the Moon's near side.

The sinuous feature appears to bear the mineralogical signature of rocks that were present before the impact that made the crater.

The deposit is interesting because it is part of a sheet of impact melt, the cooled remains of rocks melted during an impact.

The assumption was that the impact energy would the elemental composition thoroughly during the liquid phase, mixing all the rock types together into an indistinguishable mass.

Identifying any pre-impact mineral variation would be impossible but this distinct feature found at Copernicus suggests that pre-existing mineralogy isn't always blended away by the impact process.

Deepak Dhingra

"The indications are that impact melt deposits aren't bland," said Deepak Dhingra, a Brown graduate student who led the research.

"The implication is that we don't understand the impact cratering process quite as well as we thought."

The findings are published in online early view in the journal Geophysical Research Letters.

Reference
"Mineral analysis of lunar crater deposit prompts a second look at the impact cratering process": doi/10.1002/grl.50255/abstract

Read more of this article at Phys.org

Ice Melt may explain Antarctica's sea ice expansion

Climate change is expanding Antarctica's sea ice, according to a scientific study in the journal Nature Geoscience.

The paradoxical phenomenon is thought to be caused by relatively cold plumes of fresh water derived from melting beneath the Antarctic ice shelves.

This melt water has a relatively low density, so it accumulates in the top layer of the ocean.

The cool surface waters then re-freeze more easily during Autumn and Winter.

This explains the observed peak in sea ice during these seasons, a team from the Royal Netherlands Meteorological Institute (KNMI) says in its peer-reviewed paper.

Climate scientists have been intrigued by observations that Antarctic sea ice shows a small but statistically significant expansion of about 1.9% per decade since 1985, while sea ice in the Arctic has been shrinking over past decades.

The researchers from the KNMI suggest the "negative feedback" effect outlined in their study is expected to continue into the future.

They tried to reproduce the observed changes in a computer-based climate model.

The sea ice expanded during Southern Hemisphere autumn and winter in response to the development of this fresh, cool surface layer, which floated on the denser, warmer salty sea water below.

Richard Bintanja

This fresh water is ultimately derived from enhanced melting at the base of the Antarctic ice shelves.

"Sea ice around Antarctica is increasing despite the warming global climate," said the study's lead author Richard Bintanja (Bintanja.NL), from the KNMI.

"This is caused by melting of the ice sheets from below," he told the Reuters news agency.

But there are other plausible explanations for Antarctic sea-ice expansion.

Paul Holland of the British Antarctic Survey (BAS) stuck to his findings last year that a shift in winds linked to climate change was blowing ice away from the coast, allowing exposed water in some areas to freeze and make yet more ice.

Paul Holland

"The possibility remains that the real increase is the sum of wind-driven and melt water-driven effects, of course. That would be my best guess, with the melt water effect being the smaller of the two," he told the London Science Media Centre.

The study in Nature Geoscience also asserts that the cool melt water layer may limit the amount of water sucked from the oceans that falls as snow on Antarctica. Cold air can hold less moisture than warm air.