Scientists have drilled into one of the most isolated depths in all of the world’s oceans: a hidden shore of Antarctica that sits under 740 meters of ice, hundreds of kilometers in from the sea edge of a major Antarctic ice shelf. Humans have never glimpsed this place; reaching it required seven years of planning and 450 tonnes of fuel and gear. But understanding what is happening down there, so far from human view, will be crucial for predicting the future fate of Antarctica’s ice sheets amid rising temperatures. The researchers, whom I reached in their remote location by satellite phone, report that they have already discovered a curious signature of environmental change, with potential implications for the stability of the enormous ice sheet.
The team has drilled into a submerged area called the “grounding zone,” where the massive Whillans Ice Stream (located on the continent) oozes off the coastline of West Antarctica, feeding into a vast slab of glacial ice that floats on the ocean. This slab, called the Ross Ice Shelf, covers an area equal to that of France. “We’ve entered a narrow estuary of the Ross Sea that comes into this area, underneath the floating ice,” says Ross Powell, a glaciologist from Northern Illinois University (N.I.U.) who, along with two other researchers, is co-leading a team of 40 scientists, ice drillers and technicians who were flown out to the West Antarctic Ice Sheet on ski-mounted planes. (I accompanied a number of them on an Antarctica expedition in 2013. Both that expedition and this one was funded by the National Science Foundation.) This isolated cavity of seawater, down at the grounding zone, sits deep beneath the back corner of the ice shelf—850 kilometers back from where the edge of the ice meets the open sea.
The grounding zone—where the ice lifts off the muddy bottom of what would be the Antarctic shoreline if there were no ice, and begins to float on the ocean—serves as a brake, controlling the speed of the glaciers feeding into it. And speed is crucial when it comes to global warming. Some glaciers on the perimeter of West Antarctica are receiving increased heat from deep, warm ocean currents, which melt ice from the grounding line, releasing the brake and causing the glaciers to flow and shed icebergs into the ocean more quickly. Some glaciers along the Amundsen Sea coast of West Antarctica (hundreds of kilometers east of Whillans) have already accelerated by up to 60 percent due to this process.
The Whillans Ice Stream and a handful of major glaciers on either side of it are considered relatively resistant to these ocean-driven effects. Unlike most glaciers in Antarctica, Whillans is currently slowing down a little each year—part of a complex cycle of mechanical feedback that causes some glaciers to periodically stop and start again. And in 2007, a team of researchers using ice-penetrating radar reported finding a wedge of sediment 30 meters thick at the grounding zone of the Whillans Ice Stream. This sandy heap actually causes the oozing ice to slow, pile up and thicken slightly behind it—providing a buffer that may stabilize the ice sheet in the face of those warm currents. That’s the theory, at least, but no one had ever looked directly at a grounding zone until this week. The team’s first glimpse already calls into question our long-held assumptions about the long-term stability of these glaciers.
Muck means life
The Whillans drill camp sits amidst a plain of wind-scoured snow, 84 degrees south of the equator. The Transantarctic Mountains are sometimes visible 95 kilometers to the south; the South Pole sits on a high plateau behind those mountains, 625 kilometers away.
The Antarctic summer temperature hovered in the 20s Fahrenheit (–6.5 to –1.5 degrees Celsius) last week—warmer than parts of the American Midwest right now—and earlier this week it hit a sweltering 34 degrees F (1 degree C). The single-person sleeping tents are slowly sinking as the ambient body heat of their occupants, along with the absorption of warmth from 24-hour daylight melts the snow underneath. Tristy Vick-Majors, a microbiology graduate student from Montana State University describes a “controlled face plant” maneuver required to enter her own sunken quarters. Sleeping isn’t all that easy, by the way. The tents, ironically, can become uncomfortably warm. The scientists are working round-the-clock shifts, sometimes lasting 20 hours. And just to make things really fun, two diesel generators, each the size of an automobile, roar nonstop as they crank out 450 kilowatts of electricity to power the drill.
A team of ice drillers (a rare profession, but crucial in Antarctica) spent three days boring a hole through the ice last week. They did this using a jet of hot water gushing from the end of a Kevlar hose a kilometer long and as big around as an ankle. As the hole deepened, the hose was unreeled progressively into it.
The drillers encountered an unexpected glitch part way down but one that is scientifically interesting. The drill’s filters, which clean water being pumped out of the borehole, became clogged with black dust—“volcanic ashes from some past large volcanic eruption,” speculated Slawek Tulaczyk, a glaciologist from the University of California, Santa Cruz, who has studied this region for two decades and co-leads the drilling project. Finding a layer of ash in the ice wouldn’t be surprising: the West Antarctic Ice Sheet straddles a broad continental rift that is known to harbor volcanoes, some of them exposed on the surface and others sealed under ice. Ash spewed out of those volcanoes has periodically settled on the ice sheet; that ash, covered by falling snow over thousands of years, compresses into a thin layer suspended in the accumulating ice.
The drillers finally reached the bottom of the ice sheet on January 7 at 3:55 P.M. Pacific time. The water level in the borehole shot up six meters, indicating that pressurized seawater from beneath the ice had spurted into the bottom of the hole. When the drill’s metal nozzle was raised from the hole, workers found globs of rough, sticky mud clinging to it—evidence that the bottom really had been reached. Reed Scherer, a micropaleontologist from N.I.U., dabbed some of that mud onto a glass slide and slipped it under the lens of a small, folding field microscope. He spotted the glassy shards of ancient diatom shells—the remains of microscopic phytoplankton that lived here at warmer times in the past, when a shallow sea covered much of West Antarctica. One type of diatom shell that he saw, shaped like a short, segmented worm, is extinct today but lived between 10 million and six million years ago.
Pebbles hold the secret
Soon thereafter, researchers lowered a video camera into the hole. Through nearly a kilometer of slow descent the camera showed the undulating, mirrorlike walls of the ice borehole scrolling past. Then, 715 meters down, the image suddenly went black, clouded by thick wisps of silt and clay that had been liberated from the ice as the drill melted its way through. The bottom few feet of ice is probably cluttered with such debris, picked up by the glacier as it slid over the hidden face of Antarctica for thousands of years.
The camera soon emerged from this “black zone” (as people at camp are calling it) into an open expanse of crystal clear seawater beneath the ice. This thin sliver of ocean reaching under the ice turned out to be 10 meters deep, and the camera came to rest on the bottom beneath it, revealing it to be muddy and strewn with pebbles—a flat, barren tract, devoid of any obvious signs of large marine life such as brittle stars, sponges or worms.
The pebbles scattered on the bottom offered an immediate clue about the physical environment beneath the ice sheet here. “You don’t get that sort of material on a regular seafloor,” Powell says. “Normally at the ocean floor, at 700 meters depth, what you’re accumulating is very fine material”— dust or silt small enough that it could be carried by currents or winds far from land without settling out. This is what the team found two years ago when they drilled into Subglacial Lake Whillans, 95 kilometers upstream of the grounding zone; the ice there is melting off the underside of the glacier very slowly, at a rate of several dime-thicknesses per year, as heat seeps up from Earth’s deep interior. But here at the grounding zone the underside of the ice may be melting more quickly. “These stones were sitting on the seafloor after having dropped out from the ice as it was melting,” Powell says. That information could eventually help them estimate an important number: the rate at which the ocean water is melting ice at the grounding zone.
Several cores of mud have been raised from the bottom since the team got that first glance. Some of the pebbles are granite or quartz. The geology of the continent beneath Antarctica’s ice is virtually unknown but these rocks turn out to be similar to what is seen in parts of the Transantarctic Mountains. The broad rift zone of West Antarctica is thought to resemble the basin and range region of the American West where stretching of continental crust has produced an alternating topography of uptilting mountain ranges separated by low basins filled with sediments. Those chunks of granite and quartz, Tulaczyk says, may originate from a few kilometers upstream, where the Whillans Ice Stream slides over one of those western U.S.–style mountain ridges.
That hidden ridge forms a sticky spot, which influences the behavior of the Whillans Ice Stream in profound ways: Although other glaciers flow continuously, the Whillans stands still most of the time but then lurches forward twice a day, advancing roughly 45 centimeters each time. These lurches produce icequakes, which are equivalent to major magnitude 7 earthquakes and can be detected by seismometers hundreds of kilometers away. People on the ice don’t notice them simply because they unfold so slowly—at a “glacial” pace—over a 30-minute period. The twice-daily lurches and icequakes are thought to arise from ocean tides lifting the ice so that it can slide over the sticky spot, relieving mechanical strain that has built up on the glacier since the last high tide.
The cores of mud lifted up from the subglacial seabed have already produced a striking discovery: the scattered pebbles that were seen on the bottom occur only in a thin surface layer of mud. Below that the mud contains only sand. “From the looks of it, there’s been quite a change in the environment,” Powell says.
That change could have happened five years ago or maybe 500 years ago. In the months ahead Powell and his graduate student Timothy Hodson will measure the orientation of tiny magnetic mineral grains up and down the mud cores, allowing them to determine how long ago the mud and rocks were laid down and therefore when the environmental change happened. It will likely reveal something important about the stability of the grounding zone in this part of West Antarctica, an area long thought to be stable. In this dark place, so far from human eyes, significant environmental change may already be underway, which could impact how quickly the ice sheet slips into the sea and, subsequently, how quickly global sea levels may rise.
The finding and its repercussions are very preliminary. The researchers need to bring their cores back to the U.S. and study them so they can date when the changes happened, consider other lines of evidence and come to their own conclusion about what kind of environmental change may have occurred.
The water in the borehole is continually refreezing, and the hole itself is gradually squeezing shut due to the extreme pressure of the surrounding ice. But the team plans to keep it open until January 20 or so, during which time they will also take biological samples from the grounding zone. I will follow up soon with a post describing the search for life—microbial, animal or otherwise. Nothing especially large or ferocious was seen when the camera returned its first, fuzzy pictures of the bottom. But more might be revealed as the biologists raise and closely examine samples of the mud and water.