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Island time

Scientists pursue paleoclimate, deglaciation records from atop Roosevelt ice dome

 

Roosevelt Island isn’t a place you go for vacation unless you’re really into cold and snowy places sans the après-ski amenities. Or any amenities whatsoever.

Not much more than a large, icy bump on the northern edge of the nearly Texas-sized Ross Ice Shelf, Roosevelt Island is the site of an international research campaign to learn more about the climate and deglaciation history of the region for the last 30,000 years or more.

The study is called the Roosevelt Island Climate Evolution (RICE) project, which involves drilling a 750-meter-deep ice core from near the ice divide where the ice begins to flow in different directions, not unlike the split of the watersheds at the Continental Divide of the Americas. New Zealand is leading the effort, with significant support and collaboration from the United States. Denmark, the United Kingdom, Germany, Australia, Italy and China are also involved.

“What gives RICE, in my opinion, such remarkable potential is its location,” said Paul Mayewski, director of the Climate Change Institute at the University of Maine and a principal investigator on the RICE project, which is partly funded and supported by the National Science Foundation (NSF).

“It is right on the edge of an awful lot of the current climate impacting Antarctica,” he explained. “Sea ice extent has changed dramatically over the last few years. [It’s] a place where the invasion of marine air masses and the impact of the warming ocean has become very important.

“It’s in a very sensitive spot,” he added.

About 18,000 years ago, during the Last Glacial Maximum when ice extent in both hemispheres reached much farther than today, the Ross Ice Shelf was actually part of a much greater ice sheet. Then the world started to warm, and the ice sheet that once protruded into the Ross Sea retreated back rapidly over just a few thousands of years.

The grounding line where ice meets bedrock for the West Antarctic Ice Sheet in the Ross Sea region finally stabilized about 2,000 years ago, leaving behind Antarctica’s largest ice shelf — a vital plug into which numerous glaciers and ice streams flow. Its disappearance would unleash a great deal of ice into the ocean, raising sea level and likely flooding coastal areas around the world.

And there’s evidence that the Ross Ice Shelf has disintegrated numerous times in the past, with hints that it has happened even within the last million years, according to Howard “Twit” Conway, a research professor at the University of Washington. He serves as the co-chief scientist on the RICE project, alongside Nancy Bertler, a researcher from the Joint Antarctic Research Centre at Victoria University and GNS Science, who leads the New Zealand team, and Dorthe Dahl-Jensen from the Niels Bohr Institute-University of Copenhagen.

“We want to understand what happened in the past so we can gain insight into what might happen in the future,” Conway explained.

For this reason, glaciologists like Conway want to fine-tune the picture of ice sheet retreat that came into focus in 1999 based on his work and others, and was published in the journal Science.

Conway was part of a team that first visited Roosevelt Island, a dome of ice about 100 kilometers long and 60 kilometers wide, in the late 1990s. Their measurements of ice thickness, stratigraphy, accumulation rate and other parameters allowed them to estimate the age of the ice and the thinning history of the island. That information, when combined with other data from the Ross Sea region, created a rough timeline for the deglaciation of the West Antarctic Ice Sheet.

The RICE ice core will add detail to that timeline — how the ice sheet responded to past changes in climate and sea level.

“We will cover a time period of dramatic change over Antarctica,” Mayewski said. “The ice core is a beautiful dipstick back in time at the northern most edge of the Antarctic continent proper.”

Researchers estimate the ice core may be between 30,000 and 150,000 years old. They believe that the core will contain a high-resolution paleoclimate record that at least covers the transition from the glacial period of great ice sheets to the onset of the warming period known as an interglacial.

Co-investigator Ed Brook, a principal investigator on the project from Oregon State University, will measure atmospheric methane trapped in the ice core. That data will provide actual measurements of the age of the ice core.

Meanwhile, Mayewski’s lab will analyze as many as 40 different chemical elements in the ice core, which his team can use to track various atmospheric patterns that influence not only climate but ocean circulation, such as the west winds, or westerlies, which are affecting deep ocean patterns. Polar scientists believe that the strengthening of the westerlies is driving warmer ocean water onto the shallow continental shelf and thinning ice shelves that hold back glaciers that drain the interior of ice sheets.

Their work will also define what an air mass known as the Amundsen Sea Low was doing over the course of those many millennia. The group is even developing methods for tracking the powerful katabatic winds that blow down from the interior of the continent.

“We use chemistry as a fingerprint for the source, pathway and strength of air masses,” Mayewski explained.

They’ll employ newly developed laser-based technology that will allow University of Maine scientists to sample the ice core at extremely fine detail, even in the lower parts of the core were the annual layers are more compressed.

“Our laser technology for sampling trace elements will be very valuable for picking up annual layers down to greater depths than has ever been done before,” Mayewski said. “We’re now taking ice coring [analysis] down to the storm level. … We believe we will be able to tell the difference at great depths between years with many storms and not so many storms.”

That’s important for a couple of reasons, according to Mayewski. First, researchers are interested in linking what conditions are like in years with high number of storm events. In a way, he said, the paleoclimate history can become a weather record as well. 

“After all, climate is the amalgamation of weather events, and it is important to know if the strength and frequency of storms has changed in the past in order to make better predictions for the future,” he explained.

Second, climatologists like Mayewski are interested in learning more about abrupt climate change events and whether there are any warning signs prior to Mother Nature suddenly flipping the switch. He said it’s reasonable to believe that more storms may be associated with an unstable climate teetering on a new regime.

“That would be an early-warning system for abrupt climate change,” he said.

The RICE project got under way during the 2010-11 season, though the ice-coring effort didn’t begin until last year because of problems in transporting the newly designed and New Zealand-built drill from Greenland to Antarctica, according to Conway.

However, he and a small U.S. team did make the 650-kilometer-long flight from McMurdo Station to the island that first year to begin measurements of the ice-flow rate at the surface, along with radar imaging of the ice layers, which feeds into the calculus involved in determining the thickness of Ross Sea Ice Sheet thousands of years ago.

Conway and collaborator Richard Hindmarsh from British Antarctic Survey (BAS) will return to re-measure with GPS a grid of 140 poles that he and his team installed over 60 kilometers in 2010-11.

“The primary motivation for those poles is to figure out thickness changes going on right now and where they’re going on,” he explained. Hindmarsh will also bring the BAS phase-sensitive radar to measure thinning rates directly. 

The New Zealand team expects to complete drilling of the ice core. Last season, New Zealand colleagues set up the drill and infrastructure, and recovered 130 meters of ice. When drilling to the bed is complete in January 2013, co-investigator Bob Hawley at Dartmouth College and graduate student Alexandra Giese will conduct what’s called borehole logging — measuring depth profiles of temperature and optical stratigraphy.

“It’s a cool little camp. About 12 people are needed for drilling, core handling and camp duties,” said Conway, whose team will be based at the New Zealand field camp and make day trips for their GPS readings and radar measurements. The U.S. Antarctic Program is providing flight support to the camp and for flying the ice cores back to McMurdo Station.

The RICE program is one of three projects this coming season for the well-traveled glaciologist. He and co-investigator Paul Winberry from Central Washington University will study conditions beneath Beardmore Glacier, which flows through the Transantarctic Mountains to the Ross Ice Shelf.

Conway said conditions beneath the ice play a big role in how the glacier flows. Together with post-doc Michelle Koutnik and graduate student Mike Hay, they will use GPS, radar and seismic methods to measure ice flow and to image the bed conditions. Those data will be used in a computer model of how East Antarctic glaciers may respond to future changes in climate and sea level.

“One goal of this work is to determine what might happen if [in theory] you remove the Ross Ice Shelf,” Conway said.

A third project will take Conway to West Antarctica with John Stone and graduate student Perry Spector from the University of Washington, on a reconnaissance mission to find a location for a yet-to-be-proposed attempt to recover rocks from below the ice sheet.

Stone uses a technique called surface exposure dating, which determines how long rocks have been bombarded by secondary particles that result from cosmic rays hitting the Earth’s atmosphere. The dating method is based on the build-up of rare cosmic-ray-produced isotopes — the higher their concentration, the longer a rock must have been exposed.

In the case of the subglacial rock, Stone and team would use the technique to determine if and when the rocks had previously been exposed at the surface. That would help answer the questions of whether the West Antarctic Ice Sheet collapsed completely in the past, and if it happened repeatedly as scientists suspect.

Recent evidence for such belief has come from sediment cores drilled under the ice shelf and sea ice in the Ross Sea region. A 2009 paper in Nature by David Pollard and Robert M. DeConto that recreated ice sheet variations over the past five million years suggested that changes between extreme glaciation, Antarctica of the present-day and a much diminished ice sheet, happened on timescales measured in only a few thousand years, as ice shelves that buttress the glaciers disappeared.

“Many outlet glaciers are speeding up today because of changes at the grounding line,” Conway said.

NSF-funded research in this story: Howard Conway and Ed Waddington, University of Washington, Award No. 0944307; Ed Brook, Oregon State University, Award No. 0944021; Bob Hawley, Dartmouth College, Award No. 0943466; Paul Mayewski, Karl Kreutz and Andrei Kurbatov, University of Maine, Award No. 1042883; Paul Winberry, Central Washington University, Award No. 1141889; Howard Conway, University of Washington, Award No. 1141866; and John Stone, Howard Conway and Dale Winebrenner, University of Washington, Award No. 1142162.

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Curator: Peter Rejcek, Antarctic Support Contract | NSF Official: Winifred Reuning, Division of Polar Programs