Scientists Forge through Severe Sea Ice to Better Determine Why Antarctica’s Glaciers are Collapsing [Slide Show]

On the morning of January 7, 2010, a bright orange ship, squat and round-bellied, passed the northern tip of the Antarctic Peninsula. The Nathaniel B. Palmer, a 94-meter research icebreaker serving the U.S. National Science Foundation, had chugged southward for three days since leaving port in Punta Arenas, Chile, at the southern tip of South America. It had weathered a roller coaster of 8- to 12-meter sea swells, and winds over 100 kilometers per hour, as it crossed the Drake Passage between South America and Antarctica. The ship, with two dozen scientists on board, had come to investigate the effects of climate change on the thawing peninsula.

The Antarctic Peninsula has warmed by more than 2 degrees Celsius in recent decades—four times faster than other parts of the planet. This heating has triggered a dramatic series of glacial ice collapses: since 1980, over 5,000 square kilometers of floating glacial ice, 200 to 300 meters thick, has crumbled into the ocean. Those floating ice shelves had helped to stabilize glaciers behind them on land, slowing the glaciers’ flow into the sea. But with the ice shelves gone, the glaciers have accelerated into the ocean, speeding up by 2- to 9-fold.

» View the Antarctic Research Slide Show

The scientists on board the Palmer planned to investigate the mechanisms of those collapses. They also hoped to put the sudden, recent changes into a broader context, by reconstructing the history of ice shelves and glaciers in this part of Antarctica since the close of the last ice age, roughly 12,000 years ago.

As the Palmer sailed along the peninsula, multi-beam sonars on its underside fired chirps into the water—audible on every deck, in every cabin, every few seconds, day and night. Those pings painted a swath of orange-yellow-green across a computer monitor in a crowded laboratory on Deck 1—a topographic map of the ocean floor, with colors representing different depths. The swaths of color revealed undersea canyons that human eyes have never witnessed—deep grooves, 1,000 meters down, that glaciers had carved as they advanced outward from the Antarctic coast over the seafloor during the Ice Age.

Another set of sonars, operating at different frequencies that would penetrate the seafloor, returned images of the layers of sediment that have accumulated over the millennia in certain areas. Those layers held a record of glacial activity: coarse gravels deposited as a glacier 1,000 meters thick slithered over the ocean floor; finer muds laid down after the glacier retreated but the area was still shaded by a floating ice shelf 300 meters thick; and finally, layers of mud rich in ancient diatoms, microscopic organisms deposited after the ice shelf retreated and allowed sunlight to pierce cold, open water between the seasonal freezing of ice to about a meter thick.

In places where the sonar showed especially thick layers of sediment, the ship stopped. A crane swung over its rear deck, 1,000 meters of cable was spooled into the water and a core of that sediment was extracted from the ocean floor.

When a core was laid out on the laboratory on Deck 1, Eugene Domack, a marine geologist with Hamilton College, examined it, centimeter by centimeter with an eyepiece, to document its sequence of layers. Stefanie Brachfeld, a geologist from Montclair State University, analyzed the magnetic orientations of microscopic mineral grains in the sample. This sequence of changing orientations, which track movements in Earth's magnetic poles over thousands of years, would help to document the age of the sediment layers in places where organic carbon was too sparse to allow carbon 14 dating. A team of paleobiologists also sampled the microscopic shells of ancient organisms in the core for clues about the changing climate.

On January 10 the Palmer followed one of the glacially carved seafloor canyons into Prince Gustav Channel—a narrow corridor between the jagged, glaciated peaks of the Antarctic Peninsula to the west and the bare, sandstone buttes of James Ross Island to the east. The ship pushed south through a meter of ice at a steady five knots, rocking and grinding as it went—creating the impression that it was bumping along a hard, dirt road rather than floating on 700 meters of water.

Scientists on board hoped to push southward to the site of Larsen B—the largest ice shelf collapse to date, which occurred in 2002. But severe sea ice would eventually halt the ship's progress on three different occasions. The researchers still managed to accomplish many of their research objectives, but only through a mixture of ingenuity and pure tenacity.



    Fragmented sea ice, or pack ice, seen from the deck of the icebreaker, Nathaniel B. Palmer. Heavy sea ice in the Weddell Sea, on the east side of the Antarctic Peninsula, makes navigation extremely difficult even for large icebreakers. Tidal currents can rapidly compress the ice floes together, trapping a ship—as happened to the Palmer for 24 hours on January 30-31, 2010, during the excursion when the photos in this slide show were taken.


    Geologist Greg Balco from the Berkeley Geochronology Center collects rock samples from a mountain overlooking Sjögren Fjord on the Antarctic Peninsula. By measuring a rare isotope in the rock, Balco can determine how long the rock has been exposed to sunlight—and therefore how recent it was that thick Ice Age glaciers last covered this peak.


    This granite boulder does not match the surrounding bedrock. A glacier transported it to this location thousands of years ago, and later dropped it here as the ice receded. These rocks, called glacial erratics, can be used to map the flow of ancient glaciers.


    The bedrock on a mountain overlooking Sjögren Glacier is covered in scrape marks left by the glacier when it was much thicker and skidded over the mountain long ago. The orientation of the scars reveals the direction that the glacier flowed.


    A sensor is lowered through 700 meters of sea water filling a fjord on the Antarctic Peninsula. The sensor will measure temperature, salinity and the speed and direction of currents as it descends—allowing scientists to map the plumes of fresh meltwater bleeding off of coastal tidewater glaciers.


    Workers on the rear deck of the Nathaniel B. Palmer haul in a four-meter-long core of sediment that was extracted from the seafloor 1,300 meters below. Sediment cores can provide a record of when the area was covered by a floating ice shelf or even by a gigantic, grounded glacier that rested on the seafloor.


    The shells of tiny organisms, called foraminifera, that lived thousands of years ago are found in sediment cores taken from the sea floor. Scott Ishman, a paleoecologist from Southern Illinois University, studies them as ancient environmental markers. The shells shown here belong to the same species. But the robust form (on the left) occurs in areas with open water or moderate sea ice, whereas the “gracile” forms (center and right) occur in areas covered by heavy sea ice or thick ice shelves. These particular shells are about 0.2 millimeters across.


    This silica shell of an ancient diatom found in a sediment core taken from the seafloor off the Antarctic Peninsula in only. Amy Leventer, a paleobiologist at Colgate University, uses diatoms as proxies of past environments in Antarctica. The existence of the species shown here, Thalassiosira antarctica, indicates a time of relatively warm surface waters—meaning a few degrees above freezing.


    A mishmosh of microscopic diatom shells, thousands of years old, was found in certain seafloor sediments off the coast of Antarctica. The big, angular, rod-like diatom at the center, Eucampia antarctica, grows in different shapes depending on the amount of sea ice. Flat rods, like the one shown here, occur in waters covered with heavy sea ice, limiting access to sunlight. When sea ice wanes and sunlight is more plentiful, this species grows horns on either end of its shell. By analyzing the shapes of Eucampia diatoms found in the layers of a sediment core, Leventer can reconstruct how local conditions shifted over time.


    A team of researchers disembarks from the icebreaker to take samples. The researchers will quantify pockets of melt water in the sea ice, and identify microscopic diatoms locked inside the ice.

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