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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.
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.