Monthly Archives: November 2011

Pine Island Glacier: A Quest to Understand Antarctic Ice Loss

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NASA recently posted a press release about an upcoming expedition to Pine Island Glacier Ice Shelf, a key piece of real estate in Antarctica that’s slipping into the ocean at an increasingly worrisome pace. This month, in fact, an aircraft participating in Operation IceBridge spotted a lengthy crack cutting across the massive sheet of floating ice. There wasn’t much room for many details in the release, so here’s a longer description of the upcoming expedition from Goddard’s cryosphere writer, María José Viñas, for polar science aficionados.


An international team of researchers will helicopter onto thePine Island Glacier ice shelf, one of Antarctica’s most active, remote andharsh spots, in mid-December — weather permitting. Their objective: to determinehow changes in the waters circulating under the fast-melting ice sheet arecausing the glacier to accelerate and drain into the sea.

If all goes to plan,the multidisciplinary group of 13 scientists, led by NASA’s emeritusglaciologist Robert Bindschadler and funded by the National Science Foundation(NSF) and NASA, will depart from McMurdo stationin mid-December and spend six weeks on the ice shelf. The team will use acombination of traditional tools and sophisticated new oceanographicinstruments to measure the ocean cavity shape underneath the ice shelf. Theyaim to determine how streams of warm water enter this cavity, move toward thevery bottom of the glacier and melt its underbelly, making it dump more than 19cubic miles of ice into the ocean each year.

“The project aims to determine the underlying causesbehind why Pine Island Glacier has begun to flow more rapidly and dischargemore ice into the ocean,” saidScott Borg, director of NSF’s Division of Antarctic Sciences, the group thatcoordinates all U.S. research in Antarctica on the southernmost continent and surrounding oceans.”This could have a significant impact on global sea-level rise over thecoming century.”


“Darn hard to get to”

Pine Island Glacier has long been on the radar screen of Antarcticresearchers.

“Once satellite measurementsof Antarctica started to accumulate and we began to see which places werechanging, this area lit up as a spot where there was a large change going on,”Bindschadler said.

Bindschadler was the first person to ever set foot on thisisolated, wind-stricken corner of the world in January 2008. Previously,scientists doubted it was even possible to reach the crevasse-ridden ice shelf.But Bindschadler used satellite imagery to identify an area where planes couldland safely.

“The reason we haven’t gone therebefore is that it’s so darn hard to get to,” Bindschadler said. “So provingthat landing was doable was a relief.”

The glaciologist’s joydidn’t last: the ground proved to be too hard for the planes transporting theinstruments to land repeatedly. Logistics experts determined they would have touse helicopters to transport scientists and instrumentation in and out the iceshelf, and the whole plan for field campaigns had to be redesigned around thehelicopters’ availability.

Almost four years after thisfirst landing, Bindschadler and his team will be returning to the ice shelf tostudy its innards.

Scientists have determined that it’s the interaction ofwinds, water and ice that’s driving ice loss. Gusts of increasingly stronger westerlywinds push the Antarctic Circumpolar Current’s cold surface waters away fromthe continent: then, warmer waters that normally hover at depths below thecontinental shelf rise. The lifting warm waters spill over the border of thecontinental shelf and move along the floor, all the way back to the groundingline—the spot where the glacier comes afloat— causing it to melt. The warmsalty waters and fresh glacier meltwater combine to make a lighter mixture thatrises along the underside of the ice shelf and moves back to the open ocean, meltingmore ice on its way out. But, how much more ice melts?  Bindschadler and his team need to findout to improve projections of how the glacier will melt and contribute to sealevel rise.

“All existing data (satellite images, variability of winds,submarine measurements) say this a highly variable system”, said Bindschadler.“But they’re all snapshots in time. Our team will be deploying instrumentationthat will get a longer record of the variability.”

Profiling oceanwaters
One of the first tasks for the teamwill be using a hot water drill to make a 500-meter deep hole through the iceshelf. Once the drill hits the ocean, the scientists will send a camera to peerinto the ocean cavity, observe the underbelly of the ice shelf and analyze theseabed lying 500 meters below the ice.

Then, they will lower a setof instruments that Tim Stanton, an oceanographer with the Naval PostgraduateSchool, has built. The primary instrument in the package is
an ocean profiler, which will move up and down avertical cable that connects it to a communication instrument package on thesurface of the ice shelf. As it moves, the profiler will measure temperature,salinity and currents from 3 meters below the ice to just above theseabed. It can also be instructed to park at specific depths and gauge waterturbulence and vertical transport of heat and salt along the water column. Thedevice will send all data to the surface tower that will then transmit it toStanton’s laboratory via a satellite phone.

The profiler is controlled remotely, and Stanton can vary its sampling rate.I
t will initially do fast sampling,to observe daily changes in water properties and circulation withinthe ocean cavity.

“After about a month of fast sampling, we’ll make it reduce the numberof profiles it takes each day, to capture seasonal changes in water propertiesand circulation,” Stanton said. “If it survives its first year, we’ll switch tosuper slow sampling, to measure how much heat is coming into the cavity everyyear.”

A second holewill support another instrument array similar to the profiler but fixed toa pole stuck to the underside of the ice shelf. The fixed-depth flux packagewill make measurements very close to the interface where ice and water exchangeheat.

Another gadget connected tothe fixed-depth package will be a string of 16 small temperaturesensors deployed within the lowermost ice to freeze in and become part of theice shelf. Their mission: to measure the vertical temperature profile,data that can tell scientists how fast heat is transmitted upwards through theice whenever hot flushes of water enter the ocean cavity.

“Since the temperature of the ice shelf determines its strength, we hypothesizethat strength may decrease as warmmelting events occur within the ocean cavity,” Stanton said.
 
Stanton plans on deploying up to two sets of instruments during this fieldseason, and a third one next year. “If we get one in, I’ll be happy. If I get two, I’ll be extraordinarily happy,”he said. One of the biggest challenges in building his pack of instruments,Stanton said, was designing it to fit the hole in the ice shelf, only 20centimeters wide and 500 meters long. A tight, long hole also means that theteam will only get one shot at deploying the instruments: once the package islowered into the ocean cavity, it cannot be pulled out.

 
“I have been deploying instruments intoice floes in the Arctic for the last 10 years, so I got quite used tojust putting them in and turning on my heels and walking away. But it’s stillquite hard to do,” Stanton said.

Explosions and sledgehammers
A geophysicist with Penn StateUniversity,
Sridhar Anandakrishnan, will create tiny earthquakes to studythe shape of the ocean cavity and the properties of the bedrock under the PIGice shelf. He will be doing measurements in about three-dozen spots in theglacier, using helicopters to hop from oneplace to another.
Anandakrishnan’s technique, formally called reflectionseismology, involves generating waves of energy by setting up small explosionsor by using instruments similar to sledgehammers to bang the ice. He’ll recordhow long it takes for the waves to travelthrough ice and water, bounce off the seabed and return, and he’ll analyze thestrength of the echo. Both factors will tell him about the thickness of the iceand water.

“[The technique] is identicalto the way bats and dolphins do echolocation: they send out a sound and listento the echo – both the time and direction of the echo tell them about thedistance to their prey,” he said.

Anandakrishnan also wants tostudy the properties of the bedrock beneath the ice.

“When glaciers are slidingover the bedrock, they do it very differently depending on whether it is roughor smooth,” he said.

Finally, the geophysicistwill inspect a mysterious ridge that runs across the ocean cavity under the icesheet. This ridge was unknown to researchers when they designed their projectin the early 2000s; it wasn’t until 2009 that an unmanned submarine operated bythe British Antarctic Survey detected it. Its existence has made the scientistsrethink where they will place their oceanographic instruments under the iceshelf, so that they don’t hit the ridge while the glacier advances toward thesea.

“ThePine Island Glacier ice shelf continues to be the place where the action istaking place in Antarctica,” Bindschadler said. “It only can beunderstood by making direct measurements, which is hard to do. We’re doing thishard science because it has to be done. The question of how and why it ismelting is even more urgent than it was when we first proposed the project overfive years ago.”

Text by Maria-José Viñas. Pine Island Glacier ice tongue image originally published on the Pine Ice Glacier Ice Shelf page. Image of Bob Bindschadler on the ice shelf originally published here. Ocean profiler image originally published on the Pine Island Oceanography Program website. Image of Sridhar Anandakrishnan originally posted by the National Science Foundation.

Why Ozone Monitoring Still Matters

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Top scientists, policy makers and industry leaders are gathering in Washington this week for a four-day symposium that will feature discussions about the past, present and future health of the ozone layer. Some key questions on the agenda: To what degree are climate change and ozone depletion interconnected? And how can leaders apply lessons learned while confronting the ozone problem that dominated headlines in the 1980s to the threats posed by global climate change? In 1987, delegates from 24 nations signed the Montreal Protocol, a landmark piece of legislation that set limits on emissions of ozone-depleting substances known as chlorofluorocarbons (CFCs). Since then, every country in the world has followed suit. The video above shows what could have happened if countries had failed to regulate CFCs. But while the Montreal Protocol began the process of closing one chapter of the ozone story, the ozone layer still requires careful monitoring because other substances in the atmosphere – including climate-altering greenhouse gases – can also affect it. In the Q & A below, NASA Goddard atmospheric scientist Paul Newman offers his perspective on why the ozone story isn’t over, and how climate change will likely impact the evolution of the ozone layer in the future. To see daily updates on the health of the ozone layer, please visit Ozone Hole Watch.

The ozone layer is on the road to recovery. Why is it still such a hot topic among scientists?
It’s important to continue monitoring ozone because it’s so vital to life on Earth. Surface measurements and satellite observations confirm that ozone isn’t declining in our atmosphere anymore, so the Montreal Protocol is working. But ozone is impacted by many factors, not just CFCs. The Earth’s natural variations – like volcanic emissions, climate change, and the sun – can all impact ozone. Also, technological innovations like high-altitude aircraft or industrial chemicals can also impact it. So the ozone story isn’t over. It’s evolving.

If all of these factors influence ozone, can we say with certainty how it will change in the future?
The ozone layer is recovering from the effects of CFCs, but because of climate change, it will recover to different levels than its natural pre-industrial state. Our models show that we’re not going back to the old ozone layer, we’re going back to some new version of it. Our models also show that climate has a very different impact on ozone depending on whether you’re in the troposphere or the stratosphere.

What’s the difference between the troposphere and the stratosphere?
The troposphere is the lowest layer of our atmosphere, on average, extending up to about 7 miles above the Earth’s surface. Our day-to-day weather happens in the troposphere. The stratosphere extends from about 7 to 30 miles above the surface. While ozone is extremely important for screening harmful solar ultraviolet (UV) radiation, it’s a dangerous air pollutant at the Earth’s surface. Fortunately, about 90 percent of the planet’s ozone is in the stratosphere, while only 10 percent of is in the troposphere.



What about greenhouse gases? Do they also have different effects in the troposphere and stratosphere?

Greenhouse gases have much different effects in the troposphere and stratosphere. Carbon dioxide both absorbs and emits infrared radiation. In the troposphere, increased levels of carbon dioxide and other greenhouse g
ases block outgoing radiation, increasing the surface temperature. In the stratosphere, the increasing carbon dioxide concentrations allow greater radiation to space, cooling the stratosphere. So greenhouse gases warm the surface and cool the stratosphere.

How will climate change affect ozone in the stratosphere?
In the lower stratosphere, climate change will decrease the local ozone levels in the tropics and increase ozone in the mid-to-high latitudes. The “total ozone” will increase over its natural levels in the mid-latitudes in both the Northern and Southern Hemispheres – what some scientists call a “super recovery.”

How do you think the lessons learned from the ozone hole story are relevant to the climate change story?
There are two important science lessons from the Montreal Protocol. The first lesson is that solid science is the foundation for policy. The quality of both ground and satellite ozone observations can now detect a 1 percent change over a 10-year period. Policy makers relied on these estimates from scientists to formulate options on the regulation of ozone depleting substances. As the science evolved, the Montreal Protocol was strengthened. The science of climate change has seen similar improvements over the last few decades. Scientists continue to improve the quality of both observations and models of climate change. The improved quality of the science allows for the formulation of effective policy.

What’s the second lesson?
The Montreal Protocol demonstrates that the nations of the world can act together to solve a global problem. National boundaries are irrelevant to the stratospheric ozone layer. Emissions from countries in the Northern Hemisphere mainly caused the Antarctic ozone hole in the Southern Hemisphere. The nations of the world recognized the problem and acted together. This involved efforts between policy makers, technologists, scientists, industry, and non-governmental organizations. Technologies for replacing ozone-depleting substances have now been developed, and levels of these substances are now decreasing in our atmosphere. But we need to continue monitoring ozone and tracking how it reacts to climate gases. The story isn’t over.



Text by Alison Ogden. Videos from the Scientific Visualization Studio. Ozone vertical distribution graphic from Ozone Hole Watch. Image of Paul Newman originally published here.