Ice Loss in Northeast Greenland is Accelerating by 1kiki

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Ice Loss in Northeast Greenland is Accelerating

POSTED BY: 1KIKI
UPDATED: Monday, March 24, 2014 00:51
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Monday, March 24, 2014 12:47 AM

Goodbye, kind world (George Monbiot) - In common with all those generations which have contemplated catastrophe, we appear to be incapable of understanding what confronts us.

http://www.laboratoryequipment.com/news/2014/03/ice-loss-northeast-gre
enland-accelerating?et_cid=3827150&et_rid=366206770&type=headline

An international team of scientists has discovered that the last remaining stable portion of the Greenland ice sheet is stable no more. The finding, which will likely boost estimates of expected global sea level rise in the future, appears in Nature Climate Change.

The new result focuses on ice loss due to a major retreat of an outlet glacier connected to a long “river” of ice — known as an ice stream — that drains ice from the interior of the ice sheet. The Zachariae ice stream retreated about 20 kilometers (12.4 miles) over the last decade, the researchers conclude. For comparison, one of the fastest moving glaciers, the Jakobshavn ice stream in southwest Greenland, has retreated 35 kilometers (21.7 miles) over the last 150 years.

Ice streams drain ice basins, the same way the Amazon River drains the very large Amazon water basin. Zachariae is the largest ice stream in a drainage basin that covers 16 percent of the Greenland ice sheet—an area twice as large as the one drained by Jakobshavn.

This paper represents the latest finding from GNET, the GPS network in Greenland that measures ice loss by weighing the ice sheet as it presses down on the bedrock.

“Northeast Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet,” explains GNET lead investigator Michael Bevis of The Ohio State Univ. “This study shows that ice loss in the northeast is now accelerating. So, now it seems that all of the margins of the Greenland ice sheet are unstable.”

Historically, Zachariae drained slowly, since it had to fight its way through a bay choked with floating ice debris. Now that the ice is retreating, the ice barrier in the bay is reduced, allowing the glacier to speed up — and draw down the ice mass from the entire basin.

“This suggests a possible positive feedback mechanism whereby retreat of the outlet glacier, in part due to warming of the air and in part due to glacier dynamics, leads to increased dynamic loss of ice upstream. This suggests that Greenland's contribution to global sea level rise may be even higher in the future,” says Bevis, who is also the Ohio Eminent Scholar in Geodynamics and professor of earth sciences at Ohio State.

Study leader Shfaqat Abbas Khan, a senior researcher at the National Space Institute at the Technical Univ. of Denmark, says that the finding is cause for concern. “The fact that the mass loss of the Greenland Ice Sheet has generally increased over the last decades is well known,” Khan says, “but the increasing contribution from the northeastern part of the ice sheet is new and very surprising.”

GNET, short for “Greenland GPS Network,” uses the earth’s natural elasticity to measure the mass of the ice sheet. As previous Ohio State studies revealed, ice weighs down bedrock, and when the ice melts away, the bedrock rises measurably in response. More than 50 GNET stations along Greenland’s coast weigh the ice sheet like a giant bathroom scale.

Khan and his colleagues combined GNET data with ice thickness measurements taken by four different satellites: the Airborne Topographic Mapper (ATM), the Ice, Cloud and Land Elevation Satellite (ICESat), and the Land, Vegetation and Ice Sensor (LVIS) from NASA; and the Environmental Satellite (ENVISAT) from the European Space Agency. They found that the northeast Greenland ice sheet lost about 10 billion tons of ice per year from April 2003 to April 2012.

According to previous measurements and aerial photographs, the northeast Greenland ice sheet margin appeared to be stable for 25 years — until 2003. Around that time, a string of especially warm summers triggered increased melting and calving events, which have continued to the present day. A large calving event at the Zachariae glacier made the news in May 2013, and Khan and his team witnessed and filmed a similar event in July.

Increased ice flow in this region is particularly troubling, Khan says, because the northeast ice stream stretches more than 600 kilometers (about 373 miles) into the center of the ice sheet, where it connects with the heart of Greenland’s ice reservoir.

“This implies that changes at the margin can affect the mass balance deep in the center of the ice sheet. Furthermore, due to the huge size of the northeast Greenland ice stream, it has the potential of significantly changing the total mass balance of the ice sheet in the near future,” he adds.

Bevis agrees, “The fact that this ice loss is associated with a major ice stream that channels ice from deep in the interior of the ice sheet does add some additional concern about what might happen.”

The Greenland ice sheet is thought to be one of the largest contributors to global sea level rise over the past 20 years, accounting for 0.5 millimeters of the current total of 3.2 millimeters of sea level rise per year.

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Monday, March 24, 2014 12:51 AM

1KIKI

Goodbye, kind world (George Monbiot) - In common with all those generations which have contemplated catastrophe, we appear to be incapable of understanding what confronts us.

Oceanography: Deep ocean freshening
Nature Climate Change
Published online

The traditional view of the open ocean is that surface waters should change faster and that the deep waters should be relatively stable. Now research shows that the depths of the Southern Ocean are also rapidly freshening and warming, and that these changes are spreading towards the Equator.

Measurements are constantly revealing new aspects of the climate system that have changed, and that these changes are interrelated. The mass of Antarctic ice-sheet has decreased by 140 Gt yr-1 and most of this mass loss has occurred in the coastal region of the Amundsen and Bellingshausen Seas in West Antarctica. A careful and thorough census of the best available measurements of salinity and temperature shows that the deep waters of the Southern Ocean around Antarctica have freshened since the 1980s. These changes can now be seen to affect waters as far north as 30 °S, and are fully circumpolar and traceable as part of the deep circulation. This freshening signal represents some of the first independent evidence of where the ice loss from West Antarctica has gone.

Ocean temperature and salinity measurements below 2,000 m of high enough quality can only be taken by research ships (see Fig. 1), hence long-term records are sparse. Yet there is growing evidence that the deep oceans are important to the Earth's overall energy balance and to understanding of changes in sea level. The oceans are a critical part of the global energy balance and store more than 90% of the energy increase observed in the climate system since 1961. Numerical models of the Earth show that the decadal variability in the deep ocean can temporarily slow or accelerate surface temperature changes through altered ocean heat uptake. These deep measurements also provide observational constraints for better estimates of climate sensitivity to increasing greenhouse gas concentrations and there is evidence that the cause of the recent slow rate of temperature rise since 1998 is related to an internal adjustment in the oceans heat content.

Although there has been a focus on ocean temperatures, ocean salinity is now also being recognized as an important indicator of change in the climate system. The patterns of surface salinity have intensified, with salty regions becoming more salty and fresh waters tending to freshen. These surface changes are plausibly related to an acceleration of the hydrological cycle, and the redistribution of precipitation towards the poles. However hydrological changes are a key uncertainty in projections of sea level and the future mass balance of Antarctica. Temporal records in the Southern Ocean of salinity and temperature are therefore an important constraint and provide the evidence needed to address these questions about the climate system.

Antarctic Bottom Water (AABW) is commonly defined as water that is colder than 0 °C. These waters are formed on the Antarctic continental shelf, primarily in the Weddell Sea, Ross Sea and off the Adélie Coast. Near Antarctica, AABW is a layer 1,000 to 1,500 m thick. It is the densest water in the global ocean and feeds the deep ocean basins, with its signal spreading beyond the Equator into the northern Pacific, Indian and Atlantic oceans. It is an important element of the lower limb of the overturning circulation in the Southern Ocean. Purkey and Johnson find that the strongest freshening signals in AABW occur in the Amundsen–Bellingshausen basin and the Australian Antarctic Basin. Evidence has already emerged that AABW salinity is freshening strongly in the Australian Antarctic basin. The largest source of bottom water — the Weddell Sea — has freshened the least. This pattern of change is entirely consistent with glacier melt causing the freshening — the largest sources of melt water are the Pine Island and Thwaites Glaciers located west of the Antarctic Peninsula, and the known circulation patterns would subsequently transport it to the regions of strongest freshening. It is estimated that the fresher AABW can account for about half of the total Antarctic ice-mass loss (45±26%). Although the Southern Ocean and AABW occupy a relatively small fraction of the global ocean, the warming of the water column surrounding Antarctica could account for about 18±8% of the ~180 TW heat gain in the climate system over the late twentieth century; resulting in a rise of the Southern Ocean's sea level of 1–2 mm per year. The accompanying salinity changes also contribute a weak signal to this rise in sea level (as fresher water occupies a greater volume).

S. R. RINTOUL
Photograph of the standard equipment that is used to observe the ocean from surface to bottom. This instrument delivers the high-quality salinity and temperature measurements needed to monitor changing Antarctic bottom waters. Salinity is measured to an accuracy of better than 0.002 PSS (Practical Salinity Scale) and temperature to 0.002 °C.

Some outstanding issues remain. The freshening AABW accounts for only half of the melt from Antarctic ice-sheet. Surface waters around Antarctica are also freshening and it would seem likely that a significant fraction of the Antarctic melt ends up in these waters. Fresher surface waters are lighter and further isolate sea-ice from the warmer ocean below, and may help explain observed increases in Antarctic sea-ice cover. Closure of the freshwater budget (including changes in rainfall) in the Antarctic region will help in projecting future accumulation and melt of the Antarctic ice-sheet, and therefore our capacity to project Antarctica's contribution to sea-level rise. Although the freshening of AABW is very likely to be coupled with accelerating flow into the sea, and thinning, of the West Antarctic ice sheet, it is less clear whether the melt and subsequent freshening is the result of increased winds in the region or surface warming. Finally, attribution of this AABW freshening to human influences beyond the internal variability of the climate system has yet to be proved. This work provides the initial evidence for exploring these key gaps in our knowledge of the climate system.

"To argue with a man who has renounced the use of reason is like administering medicine to the dead."

-- Thomas Paine, The American Crisis No. V (1776)

OONJERAH
We are too dumb to live and smart enough to wipe ourselves out.

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