How many more surprises can we handle? It seems that every time we look we find more bad news. This one certainly surprises me. Scientists Drill through 2,400 Feet of Antarctic Ice for Climate Clues.
cientists 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.
Read on below for more.
The news is disturbing at best:
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.) This isolated cavity of seawater, down at the grounding zone, sits deep beneath the back corner of the ice shelf—600 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. 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 have already accelerated by up to 60 percent due to this process.
The nature of what they found is very revealing:
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.
The researchers are being very cautious about sounding alarms as they should be. In isolation these findings would be significant. In the context of eveything else we are learning they may be devistating.
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.
Recent reports have concluded that the apparent slowdown of global warming is just that: apparent. The ocean is a huge buffer and it is impossible to measure temperature changes everywhere. One thing is certain, the buffering effect has a limit. Once it is reached, global temperatures are going to rise more rapidly.
Tue Jan 20, 2015 at 11:14 AM PT: thanks for adding this to the rec list