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domingo, 12 de febrero de 2017

ESA : CryoSat reveals lake outbursts beneath Antarctic ice.- CryoSat revela estallidos debajo del lago del hielo antártico

http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/CryoSat_reveals_lake_outbursts_beneath_Antarctic_ice

Four lakes under Thwaites

8 February 2017

A novel way of using ESA’s CryoSat mission has revealed how lakes beneath Thwaites Glacier drained into the Amundsen Sea – potentially the largest such outflow ever reported in this region of West Antarctica.

This new information is helping scientists understand more about what’s going on deep below the surface of the ice and what affects how fast the glaciers flow towards the ocean.

Thwaites and its neighbouring Pine Island Glacier are the fastest-receding glaciers on the Western Antarctic Ice Sheet.

Although this huge sheet is some 2 km thick in places, much of its floor is well below sea level. This makes it is particularly vulnerable to change, especially where the warmer ocean waters meet the underside of the floating terminus of the glacier.

Understanding the movements of these glaciers is critical for predicting how the ice sheet may behave in the future and how it may affect sea level.

A paper published today in The Cryosphere explains how CryoSat measurements have been processed in a new way and reveal that, in 2013, four interlinked lakes under Thwaites drained into the ocean.

Glacier speed West Antarctica

Lakes have been found under glaciers in many parts of Antarctica and are, indeed, commonly associated with fast-flowing glaciers. However, this is the first time they have been found and observed draining into the Amundsen Sea. In addition, this emptying is thought to happen only every 20–80 years.

Water below the ice sheet plays an important role in how quickly glaciers flow towards the sea, thought to be because a layer of meltwater reduces friction between the ice and the bedrock.

In addition, when channels form under the ice they lubricate the glacier bed.

Benjamin Smith from the University of Washington and lead author of the paper said, “This is first time we’ve been able to monitor both elevation changes and ice speed in this kind of detail over such a large area.

“Without a satellite like CryoSat, we would have probably have missed the lake draining and we would have had to guess how the lake drainage might have affected the ice speed.

“Together, they tell us about how water moving at the glacier bed affects ice speed, and what processes we need to understand so that we are better equipped to predict the future of Thwaites.”

One of four lakes under the glacier

Noel Gourmelen from the University of Edinburgh explained, “Repeat observations from CryoSat over Thwaites revealed that the surface of the ice subsided by several metres as water drained away from the four lakes under the ice. The lakes totalled an area of about 700 sq km.

“On average, Thwaites carries about 135 cubic kmof ice to the sea every year, but drainage from these lakes released an extra 3.5 cubic km of freshwater.

“In addition, the speed of the glacier increased by about 10% and would have contributed to a discharge of around 150 cubic kma year between 2013 and 2014.”

Drainage is estimated to have peaked at about 240 cubic m a second, possibly the largest outflow of meltwater ever reported from subglacial lakes in this region. This peak rate is about four times faster than the River Thames in England discharges to the North Sea each year.

Before this discovery, scientists had thought that this part of the ice sheet did not store water in lakes beneath the surface for very long because abrupt drainage had not been seen before in the area.

ESA's ice misión

Mark Drinkwater, head of ESA’s Earth observation mission science, said, “Previous studies have investigated if CryoSat could be used for monitoring small vertical displacements associated with these events.

“The main issue has been the limited coverage of standard altimeter measurements. But thanks to new processing techniques, the capability of using CryoSat to both discover and monitor Antarctic subglacial lakes has vastly increased.

Tommaso Parrinello, ESA’s CryoSat mission manager, added, “CryoSat again is proving what a versatile satellite it is. Now we also have the Copernicus Sentinel-1, with both providing powerful tools for developing further understanding of the relationship between lake drainage and ice dynamics in Antarctica.”

CryoSat maps largest-ever flood beneath Antarctica
02 July 2013

Satellites track variations in Antarctica’s glacial retreat
12 December 2016

Antarctic ice safety band at risk
08 February 2016

ESA

Guillermo Gonzalo Sánchez Achutegui

Inscríbete en el Foro del blog y participa : A Vuelo De Un Quinde - El Foro!

domingo, 5 de febrero de 2017

ESA : Larsen crack .- Grieta en Larsen C

http://www.esa.int/spaceinimages/Images/2017/01/Larsen_crack

http://www.esa.int/esl/ESA_in_your_country/Spain/La_grieta_de_Larsen_C

Larsen crack

La grieta de Larsen C

1 febrero 2017

Hace ya varios años que apareció una grieta en la barrera de hielo Larsen C de la península Antártica, pero en los últimos tiempos ha ido creciendo más rápido que nunca.

Gracias a sus radares con ‘visión nocturna’, los satélites Sentinel-1 de Copernicus están vigilando la situación.

Esta animación muestra que la fisura se ha extendido unos 60 km desde enero del año pasado. Y desde principios de enero de este año, se han separado otros 20 km, por lo que, en estos momentos, la plataforma de 350 m de grosor apenas se encuentra unida por un hilo a la península. La grieta ahora tiene unos 175 km de longitud.

Cuando el iceberg se separe definitivamente de la barrera de hielo, será uno de los mayores nunca registrados, aunque es difícil pronosticar cuándo sucederá. Las barreras colindantes, Larsen A y Larsen B experimentaron un proceso similar, con partos espectaculares en 1995 y 2002, respectivamente.

Estas barreras de hielo son importantes, ya que actúan a modo de refuerzo, reteniendo el hielo que fluye hacia el mar.

Los dos satélites Sentinel-1 son fundamentales para descubrir y vigilar acontecimientos como estos, ya que son capaces de proporcionar imágenes de radar de forma continua, a pesar de que la Antártida permanece inmersa en la oscuridad durante varios meses al año.

English Versión:

(5.02 MB)

Details

Title Larsen crack
Released 30/01/2017 9:19 am
Copyright contains modified Copernicus Sentinel data (2016–17), processed by ESA
Description

A crack in the Larsen-C ice shelf in on the Antarctic Peninsula first appeared several years ago, but recently it has been lengthening faster than before. Carrying radar that can ‘see’ through the dark, the Copernicus Sentinel-1 satellites are monitoring the situation. The animation shows that the fissure has opened around 60 km since January last year. And, since the beginning of this January it has split a further 20 km so that the 350 m-thick shelf is held only by a thread. The crack now extends around 175 km.

When the ice shelf calves this iceberg it will be one of the largest ever recorded – but exactly how long this will take is difficult to predict. The neighbouring Larsen-A and Larsen-B ice shelves suffered a similar fate with dramatic calving events in 1995 and 2002, respectively.

These ice shelves are important because they act as buttresses, holding back the ice that flows towards the sea.

The Sentinel-1 two-satellite constellation is indispensable for discovering and monitoring events like these because it continues to deliver radar images when Antarctica is shrouded in darkness for several months of the year.
Id 372459

lunes, 12 de diciembre de 2016

ESA : Satellites track variations in Antarctica’s glacial retreat .-Los satélites rastrean variaciones en el retiro glacial antártico...........

http://www.esa.int/Our_Activities/Observing_the_Earth/CryoSat/Satellites_track_variations_in_Antarctica_s_glacial_retreat

Variatons in glacial retreat

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Satellites track variations in Antarctica’s glacial retreat

12 December 2016

Five satellites spanning two decades have revealed variations in the timing and pace of glacial retreat in West Antarctica. Some glaciers’ thinning spreads up to three times faster than on neighbouring tributarie, and was offset by decades.

The glaciers flowing into the Amundsen Sea have been drastically losing ice, likely due to rising sea temperatures recorded around Antarctica in recent decades.

The Pine Island Glacier is known to contribute more to rising sea levels than any other ice stream on the planet, and the neighbouring Thwaites and smaller Pope, Smith and Kohler Glaciers are also losing ice.

But the rate at which these glaciers are melting varies between them, despite their relative vicinity. Possible reasons for this include differences in glacier catchment size, bedrock, topography and hydrology.

Access the video

What remains clear, however, is that over the past 25 years, all three have seen thinning from the grounding line – where the ice stream lifts up off the land and begins to float out over the ocean – across the glacier surface.

“Scientists generally agree that it is warm ocean water that melts the floating part of the glacier, which then allows the glacier to flow more easily because it’s no longer held back by the floating ice shelf. As the glacier flows faster, it starts to become thinner,” said Dr Hannes Konrad, lead author of the study published in Geophysical Research Letters.

“If there’s not enough snow and ice accumulating higher up to compensate, the glaciers lose more and more of their mass as they flow towards the sea, and that’s exactly what we are seeing here, but the detail varies considerably between the three systems, and even within each glacier.”

Using data dating back to 1992 from the ERS-1 mission, together with information from ERS-2, Envisat, CryoSat and NASA’s IceSat, scientists from the UK’s Centre for Polar Observation and Modelling reconstructed surface heights along a series of glacial flowlines to see how thinning at the grounding lines had been passed further inland.

In 1992, all three were already experiencing height loss at or near the grounding line, with Pine Island Glacier losing height by around 1 m every year – although the interior surface was stable.

Thinning then spread steadily, first up the glacier’s main trunk, and then further inland. While the pace at which it spread across the surface varied, rates of thinning reached up to 13 km/year.

Measuring freeboard

Changes at Thwaites Glacier were more erratic. The surface at the grounding line was already falling by up to 3 m/year in 1992, but thinning ceased around 2000. In 2004, thinning continued and spread at similar rates to those seen at Pine Island Glacier, but the offset of about 10 years means that it did not spread as far inland.

The Pope, Smith and Kohler Glaciers experienced the largest falls in surface height of up to 7 m/year, most likely beginning before the data record. The thinning spread much more slowly than at Pine Island Glacier or Thwaites Glacier.

“As well as being able to routinely monitor the polar ice sheets as a whole, these results show the ability of satellites to pinpoint how individual glaciers are responding to environmental change,” said CPOM Director Professor Andy Shepherd.

“The next steps are to refine our calculations of ice loss and sea level rise from the Antarctic ice sheet as a whole, and, in turn, improve our models of what might happen in the future.”

The study is being presented today at the American Geophysical Union’s Fall Meeting held in San Francisco, USA.

ESA

Guillermo Gonzalo Sánchez Achutegui

Further reading and annotated images: NASA's Earth Observatory

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viernes, 24 de junio de 2016

NASA : Pervasive Ice Retreat in West Antarctica .- Generalizado retroceso del hielo en la Antártida Occidental

http://www.nasa.gov/image-feature/pervasive-ice-retreat-in-west-antárctica

Along the Bellingshausen Sea coast of West Antarctica, ice has been retreating inland being lost to the sea. Scientists knew this, but they lacked a full picture of the scale. Now a team of researchers has compiled a Landsat-based data set and found that such losses have been going on for at least the past four decades and along the vast majority of this coast.

“We knew that ice had been retreating from this region recently,” said Frazer Christie, a doctoral candidate at the University of Edinburgh and a co-author of the study. “Now, thanks to a wealth of freely available satellite data, we know this has been occurring pervasively along the coastline for almost half a century.”

The Bellingshausen Sea—named for the Russian Admiral who found the continent in 1820—lies to the west of the Antarctic Peninsula. Examining Landsat data collected between 1975 and 2015, the researchers mapped the approximate locations of “grounding lines” in the ice along the Bellingshausen coast. These lines mark the intersection where glacial ice flowing from the continent is connected, or grounded, to the seafloor. Any ice past the grounding line usually floats on the sea as an ice shelf. When ice is lost to the sea, the grounding line retreats. Meanwhile, the ice loss contributes to global sea level rise.

Christie and colleagues used Landsat data to locate “inflection points” on the surface of the ice that indicate the approximate location of grounding lines below. An inflection point—which can be tricky to detect by an untrained eye—is defined as the last location where the slope of the ice dramatically changes before flattening out into an ice shelf or meeting the sea.

The team combined its Landsat projections of inflection points with radar data from the European Space Agency’s ERS 1 and 2 and CryoSat-2 satellites. They found that the majority of the coastline along the Bellinghausen Sea experienced some grounding line retreat over the past four decades. The findings were published in Geophysical Research Letters.

The widespread retreat has likely been caused by warmer ocean water licking at the undersides of the floating ice near the grounding line—or as the authors write: “an ingress of relatively warm circumpolar deep water.”

The image above shows an area near Eltanin Bay, where the majority of the grounding line is found at the seaward front of the ice. It was acquired by the Operational Land Imager on Landsat 8 on March 2, 2015. The ice loss is most pronounced along the Ferrigno Ice Stream, which was named for Jane Ferrigno, a U.S. Geological Survey scientist who used satellite data (including Landsat) to map Antarctica.

“Our study provides important context for understanding the causes of ice retreat throughout Antarctica as a whole,” said Christie. “We now know West Antarctica has been changing for many decades, so the next challenge is to ascertain the key ice, ocean, and atmospheric factors responsible for such ice losses.”

Image Credit: NASA Earth Observatory images by Jesse Allen, using Landsat data from the U.S. Geological Survey
Caption: Laura Rocchio, Landsat Communication and Public Engagement Team

Last Updated: June 22, 2016

Editor: Sarah Loff

Tags: Earth, Ice, Image of the Day, Landsat,

NASA

Guillermo Gonzalo Sánchez Achutegui

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domingo, 17 de mayo de 2015

NASA : Antarctica’s Larsen B Ice Shelf: The Final Act .- Estudio de la NASA de una muestra del hielo Larsen B de la Antártida ha llegando a su Acto Final

NASA research has found that the last section of Antarctica's Larsen B Ice Shelf is likely to disintegrate before the end of the decade.

Un nuevo estudio de la NASA encuentra el último tramo restante de la Antártida de hielo Larsen B, que se derrumbó parcialmente en 2002, se está debilitando y es probable que se desintegran por completo antes del final de la década rápidamente.

More information:

http://www.nasa.gov/press-release/nasa-study-shows-antarctica-s-larsen-b-ice-shelf-nearing-its-final-act

NASA Study Shows Antarctica’s Larsen B Ice Shelf Nearing Its Final Act

A new NASA study finds the last remaining section of Antarctica's Larsen B Ice Shelf, which partially collapsed in 2002, is quickly weakening and likely to disintegrate completely before the end of the decade.

A team led by Ala Khazendar of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, found the remnant of the Larsen B Ice Shelf is flowing faster, becoming increasingly fragmented and developing large cracks. Two of its tributary glaciers also are flowing faster and thinning rapidly.

"These are warning signs that the remnant is disintegrating," Khazendar said. "Although it’s fascinating scientifically to have a front-row seat to watch the ice shelf becoming unstable and breaking up, it’s bad news for our planet. This ice shelf has existed for at least 10,000 years, and soon it will be gone."

Antarctica's Larsen B Ice Shelf is likely to shatter into hundreds of icebergs before the end of the decade, according to a new NASA study.

Credits: NSIDC/Ted Scambos

Ice shelves are the gatekeepers for glaciers flowing from Antarctica toward the ocean. Without them, glacial ice enters the ocean faster and accelerates the pace of global sea level rise. This study, the first to look comprehensively at the health of the Larsen B remnant and the glaciers that flow into it, has been published online in the journal Earth and Planetary Science Letters.

Khazendar's team used data on ice surface elevations and bedrock depths from instrumented aircraft participating in NASA's Operation IceBridge, a multiyear airborne survey campaign that provides unprecedented documentation annually of Antarctica's glaciers, ice shelves and ice sheets. Data on flow speeds came from spaceborne synthetic aperture radars operating since 1997.

Khazendar noted his estimate of the remnant's remaining life span was based on the likely scenario that a huge, widening rift that has formed near the ice shelf's grounding line will eventually crack all the way across. The free-floating remnant will shatter into hundreds of icebergs that will drift away, and the glaciers will rev up for their unhindered move to the sea.

Located on the coast of the Antarctic Peninsula, the Larsen B remnant is about 625 square miles (1,600 square kilometers) in area and about 1,640 feet (500 meters) thick at its thickest point. Its three major tributary glaciers are fed by their own tributaries farther inland.

"What is really surprising about Larsen B is how quickly the changes are taking place," Khazendar said. "Change has been relentless."

The remnant's main tributary glaciers are named Leppard, Flask and Starbuck -- the latter two after characters in the novel Moby Dick. The glaciers' thicknesses and flow speeds changed only slightly in the first couple of years following the 2002 collapse, leading researchers to assume they remained stable. The new study revealed, however, that Leppard and Flask glaciers have thinned by 65-72 feet (20-22 meters) and accelerated considerably in the intervening years. The fastest-moving part of Flask Glacier had accelerated 36 percent by 2012 to a flow speed of 2,300 feet (700 meters) a year -- comparable to a car accelerating from 55 to 75 mph.

Flask's acceleration, while the remnant has been weakening, may be just a preview of what will happen when the remnant breaks up completely. After the 2002 Larsen B collapse, the glaciers behind the collapsed part of the shelf accelerated as much as eightfold – comparable to a car accelerating from 55 to 440 mph.

The third and smallest glacier, Starbuck, has changed little. Starbuck's channel is narrow compared with those of the other glaciers, and strongly anchored to the bedrock, which, according to authors of the study, explains its comparative stability.

"This study of the Antarctic Peninsula glaciers provides insights about how ice shelves farther south, which hold much more land ice, will react to a warming climate," said JPL glaciologist Eric Rignot, a coauthor of the paper.

The research team included scientists from JPL, the University of California, Irvine, and the University Centre in Svalbard, Norway. The paper is online at:

http://go.nasa.gov/1bbpfsC

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information about NASA’s Earth science activities, visit:

http://www.nasa.gov/earth

NASA

Guillermo Gonzalo Sánchez Achutegui

> Operation IceBridge Antarctic 2014 Campaign

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domingo, 9 de noviembre de 2014

NASA: Glaciers and Mountains in West Antarctica .- Las montañas y los glaciares de la Antártida Occidental

Hola amigos: A VUELO DE UN QUINDE EL BLOG., la Agencia Espacial NASA, nos informa que : "Los glaciares y las montañas en el sol de la tarde se ven en una investigación vuelo Operación IceBridge, al regresar de la Antártida Occidental el 29 de octubre de 2014..................
La NASA está llevando a su sexto año consecutivo en octubre de vuelos de investigación Operación IceBridge sobre la Antártida para estudiar los cambios en la capa de hielo del continente, los glaciares y el hielo marino. La campaña de este año vuelve a visitar la sección de aire de la Antártida . Que la capa de hielo recientemente se encontró que era de declive irreversible................

IceBridge utiliza un conjunto de instrumentos incluye altímetro láser que, instrumentos de radar, cámaras, y un gravímetro, que es un instrumento que detecta pequeños cambios en la gravedad. Estos pequeños cambios revelan la cantidad de glaciares han perdido masa Estes. Los investigadores planean medida calculada previamente inexploradas regiones de la Antártida, como las partes superiores de Smith glaciar en la Antártida Occidental, que es el adelgazamiento más rápido que cualquier otro de los glaciares de la región. La misión también tiene previsto recopilar datos en partes de la Península Antártica, como la Larsen C, George VI y Wilkins plataformas de hielo y los glaciares drenan en em Que. El calentamiento de la Península Antártica ha sido el más rápido que el resto del continente.................

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Glaciers and Mountains in West Antarctica

Glaciers and mountains in the evening sun are seen on an Operation IceBridge research flight, returning from West Antarctica on Oct. 29, 2014.

NASA is carrying out its sixth consecutive year of Operation IceBridge research flights over Antarctica to study changes in the continent’s ice sheet, glaciers and sea ice. This year’s airborne campaign revisits a section of the Antarctic ice sheet that recently was found to be in irreversible decline.

IceBridge uses a suite of instruments that includes a laser altimeter, radar instruments, cameras, and a gravimeter, which is an instrument that detects small changes in gravity. These small changes reveal how much mass these glaciers have lost. Researchers plan to measure previously unsurveyed regions of Antarctica, such as the upper portions of Smith Glacier in West Antarctica, which is thinning faster than any other glaciers in the region. The mission also plans to collect data in portions of the Antarctic Peninsula, such as the Larsen C, George VI and Wilkins ice shelves and the glaciers that drain into them. The Antarctic Peninsula has been warming faster than the rest of the continent.

In addition to extending the data record of NASA’s Ice, Cloud and Land Elevation Satellite (ICESat), which stopped collecting data in 2009, IceBridge will also help set the stage for ICESat-2 by measuring ice the satellite will fly over.

Image Credit: NASA/Michael Studinger

NASA

Guillermo Gonzalo Sánchez Achutegui

> NASA's Earth Observatory: Operation IceBridge Turns Five

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domingo, 19 de octubre de 2014

NASA : Operation IceBridge Turns Five

Hola amigos: A VUELO DE UN QUINDE EL BLOG., la agencia espacial NASA, nos informa sobre sus investigaciones con su proyecto en la Antártica : NASA’s Operation IceBridge, ....En mayo de 2014, dos nuevos estudios concluyeron que una sección de la capa de hielo de la Antártida occidental con base en tierra había llegado a un punto de un colapso inevitable. Mientras tanto, nuevas observaciones desde septiembre 2014 mostraron hielo marino alrededor de la Antártida había alcanzado su máxima extensión desde finales del decenio de 1970........

Para comprender mejor estas diferencias dinámicos y dramáticos en la tierra y el mar de hielo de la región, los investigadores están viajando hacia el sur hasta la Antártida este mes por sexta campaña de la Operación IceBridge de la NASA. La campaña aérea, que también vuela cada año sobre Groenlandia, hace que las encuestas anuales del hielo con aviones de investigación instrumentado....

Instrumentos van de los láseres que se asignan la elevación de la superficie del hielo, los radares que "ver" debajo de él, y hacia abajo en busca de cámaras para proporcionar una perspectiva de color natural. El (DMS) de la cámara Sistema de cartografía digital adquirió la foto de arriba durante el primer vuelo científico de la misión el 16 de octubre de 2009 En el momento de la imagen, el avión DC-8 estaba volando a una altitud de 515 metros (1.700 pies) sobre pesadamente primer año compactada hielo marino a lo largo del borde del Mar de Amundsen........................

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Operation IceBridge Turns Five

In May 2014, two new studies concluded that a section of the land-based West Antarctic ice sheet had reached a point of inevitable collapse. Meanwhile, fresh observations from September 2014 showed sea ice around Antarctica had reached its greatest extent since the late 1970s.

To better understand such dynamic and dramatic differences in the region's land and sea ice, researchers are travelling south to Antarctica this month for the sixth campaign of NASA’s Operation IceBridge. The airborne campaign, which also flies each year over Greenland, makes annual surveys of the ice with instrumented research aircraft.

Instruments range from lasers that map the elevation of the ice surface, radars that "see" below it, and downward looking cameras to provide a natural-color perspective. The Digital Mapping System (DMS) camera acquired the above photo during the mission’s first science flight on October 16, 2009. At the time of the image, the DC-8 aircraft was flying at an altitude of 515 meters (1,700 feet) over heavily compacted first-year sea ice along the edge of the Amundsen Sea.

Since that first flight, much has been gleaned from IceBridge data. For example, images from an IceBridge flight in October 2011 revealed a massive crack running about 29 kilometers (18 miles) across the floating tongue of Antarctica's Pine Island Glacier. The crack ultimately led to a 725-square-kilometer (280-square-mile) iceberg.

In 2012, IceBridge data was a key part of a new map of Antarctica called Bedmap2. By combining surface elevation, ice thickness, and bedrock topography, Bedmap2 gives a clearer picture of Antarctica from the ice surface down to the land surface. Discoveries have been made in Greenland, too, including the identification of a 740-kilometer-long (460-mile-long) mega canyon below the ice sheet.

Repeated measurements of land and sea ice from aircraft extend the record of observations once made by NASA’s Ice, Cloud, and Land Elevation Satellite, or ICESat, which stopped functioning in 2009. In addition to extending the ICESat record, IceBridge also sets the stage for ICESat-2, which is scheduled for launch in 2017.

Image Credit: IceBridge DMS L0 Raw Imagery courtesy of the Digital Mapping System (DMS) team/NASA DAAC at the National Snow and Ice Data Center
Caption: Kathryn Hansen

NASA

Guillermo Gonzalo Sánchez Achutegui

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sábado, 6 de septiembre de 2014

NASA : NASA-UCI Study Indicates Loss of West Antarctic Glaciers Appears Unstoppable

Glaciers in West Antarctica’s Amundsen Sea Embayment have “passed the point of no return” according to new research based on three different lines of evidence.

Image Credit:

NASA/Eric Rignot

A new study by researchers at NASA and the University of California, Irvine, finds a rapidly melting section of the West Antarctic Ice Sheet appears to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea.

The study presents multiple lines of evidence, incorporating 40 years of observations that indicate the glaciers in the Amundsen Sea sector of West Antarctica "have passed the point of no return," according to glaciologist and lead author Eric Rignot, of UC Irvine and NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. The new study has been accepted for publication in the journal Geophysical Research Letters.

These glaciers already contribute significantly to sea level rise, releasing almost as much ice into the ocean annually as the entire Greenland Ice Sheet. They contain enough ice to raise global sea level by 4 feet (1.2 meters) and are melting faster than most scientists had expected. Rignot said these findings will require an upward revision to current predictions of sea level rise.

"This sector will be a major contributor to sea level rise in the decades and centuries to come," Rignot said. "A conservative estimate is it could take several centuries for all of the ice to flow into the sea."

Three major lines of evidence point to the glaciers' eventual demise: the changes in their flow speeds, how much of each glacier floats on seawater, and the slope of the terrain they are flowing over and its depth below sea level. In a paper in April, Rignot’s research group discussed the steadily increasing flow speeds of these glaciers over the past 40 years. This new study examines the other two lines of evidence.

The glaciers flow out from land to the ocean, with their leading edges afloat on the seawater. The point on a glacier where it first loses contact with land is called the grounding line. Nearly all glacier melt occurs on the underside of the glacier beyond the grounding line, on the section floating on seawater.

Just as a grounded boat can float again on shallow water if it is made lighter, a glacier can float over an area where it used to be grounded if it becomes lighter, which it does by melting or by the thinning effects of the glacier stretching out. The Antarctic glaciers studied by Rignot's group have thinned so much they are now floating above places where they used to sit solidly on land, which means their grounding lines are retreating inland.

"The grounding line is buried under a thousand or more meters of ice, so it is incredibly challenging for a human observer on the ice sheet surface to figure out exactly where the transition is," Rignot said. “This analysis is best done using satellite techniques."

The team used radar observations captured between 1992 and 2011 by the European Earth Remote Sensing (ERS-1 and -2) satellites to map the grounding lines' retreat inland. The satellites use a technique called radar interferometry, which enables scientists to measure very precisely -- within less than a quarter of an inch -- how much Earth's surface is moving. Glaciers move horizontally as they flow downstream, but their floating portions also rise and fall vertically with changes in the tides. Rignot and his team mapped how far inland these vertical motions extend to locate the grounding lines.

The accelerating flow speeds and retreating grounding lines reinforce each other. As glaciers flow faster, they stretch out and thin, which reduces their weight and lifts them farther off the bedrock. As the grounding line retreats and more of the glacier becomes waterborne, there's less resistance underneath, so the flow accelerates.

Slowing or stopping these changes requires pinning points -- bumps or hills rising from the glacier bed that snag the ice from underneath. To locate these points, researchers produced a more accurate map of bed elevation that combines ice velocity data from ERS-1 and -2 and ice thickness data from NASA's Operation IceBridge mission and other airborne campaigns. The results confirm no pinning points are present upstream of the present grounding lines in five of the six glaciers. Only Haynes Glacier has major bedrock obstructions upstream, but it drains a small sector and is retreating as rapidly as the other glaciers.

The bedrock topography is another key to the fate of the ice in this basin. All the glacier beds slope deeper below sea level as they extend farther inland. As the glaciers retreat, they cannot escape the reach of the ocean, and the warm water will keep melting them even more rapidly.

The accelerating flow rates, lack of pinning points and sloping bedrock all point to one conclusion, Rignot said.

"The collapse of this sector of West Antarctica appears to be unstoppable," he said. "The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers. At this point, the end of this sector appears to be inevitable."

Because of the importance of this part of West Antarctica, NASA's Operation IceBridge will continue to monitor its evolution closely during this year's Antarctica deployment, which begins in October. IceBridge uses a specialized fleet of research aircraft and the most sophisticated suite of science instruments ever assembled to characterize changes in thickness of glaciers, ice sheets and sea ice.

For additional images and video related to this new finding, visit:

http://go.nasa.gov/1m6YZSf

For additional information on the West Antarctic Ice Sheet and its potential contribution to sea level rise, visit:

http://go.nasa.gov/1oIfSlO

For more information on Operation IceBridge, visit:

http://www.nasa.gov/icebridge

The California Institute of Technology in Pasadena manages JPL for NASA.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

For more information about NASA's Earth science activities in 2014, visit:

http://www.nasa.gov/earthrightnow

NASA

Guillermo Gonzalo Sánchez Achutegui