Reading cracks in the dramatically shrinking glacial ice at Neko Harbour
Lee NarrawayThe other day the Antarctic University Expedition 2011 had a quick landing at Neko Harbour, a glaciated spot on the Antarctic Peninsula. Rather than hanging out with the penguins at the shore, this time I hiked up a snow-covered hillside with the glaciology students who had come to collect samples from it. The snows of the glaciers all around us were riven with cracks running along and across their course — a sign, University of Ottawa glaciologist Luke Copland told us, that they are under pressure, highly active despite their apparent stillness. Our group stayed within a box of footprints laid out by the professors (a safe area from any such crevasses) as the students laboriously shovelled through 1.5 metres of snow to reach the solid ice at its base. From there, they could extract the cores: thick, translucent cylinders, bubbled with air that was trapped inside the ice as it formed. These surface-level cores only go a few years back; the record to be found in deeper cores reaches as far back as 800,000 years ago. Glaciologists are consummate analyzers of gradual change — but, as the occasional crackle or boom echoing out of the surrounding area reminded us, those changes can culminate in very sudden and serious results.
Just those kinds of results are happening (and are expected to continue) as Antarctica responds to the Earth’s changing climate. Olle Carlsson, a Swedish naturalist and guide now in his twenty-first season of extensive visits to Antarctica, has been to these sites every year since 1991. He has watched them change with his own eyes. He says these glaciers at Neko Harbour were not so crevassed, and came closer to the beach, when he first saw them; ten years ago, part of Brown Bluff that we’ve walked freely through was frozen and impassible; ice all around is thinning or disappearing. Our expedition kept hearing that the insufferably adorable adélie penguins should be at the sites we were visiting; but they have moved increasingly southward, and only showed up in handfuls among the gentoos, who thrive better in low sea ice conditions.
Studies have been somewhat ambiguous on whether Antarctica, taken as a whole, has warmed significantly since record-keeping began. But at the local level things look much scarier. While high-elevation, thickly iced-over east Antarctica has kept relatively stable, the warmer western parts of the continent — the Peninsula, where we have been, and the Amundsen Sea — are showing serious warming effects. Temperatures in the Peninsula have been going up about 1˚C per decade, one of the fastest rates of warming on the planet.
The most dramatic signs so far have been the collapses of ages-old ice shelves along the Peninsula’s length: the Larsen A Shelf in 1995, Larsen B in 2002, and Wilkins in 2009. Luke, the glaciologist, points out in his characteristically soft-spoken — yet urgent — way that these collapses are, unnervingly, travelling southward along the Peninsula, one going after the other as temperatures increase. Changes in the single-degrees Celsius sound minor out of context, but from the right starting point they can make every difference: above -9˚C, ice shelves become unstable; past -5˚C, they are gone. For ice shelves near this critical range, one particularly warm year is all it takes to finish the job — which is what happened to 3,000 square kilometres of the Larsen B shelf in 2002. Some researchers are looking at mountain glaciers in the Tropics; in places like Peru and Tanzania, already existing at the threshold of temperatures too warm to sustain ice, glaciers are now vanishing at a critical rate as the thermometer creeps upward.
Antarctic ice shelves are already afloat, so they don’t directly increase sea levels when they collapse. But their breaking off from the continent opens the way for the glaciers behind them to surge forward, dumping into the water at higher speeds. The Amundsen Sea, Luke tells me, now has few glaciers left, their descent having accelerated from one metre per year to between eight and ten. Given the current rates of global warming and the continuing increase of our greenhouse gas emissions, the loss of ice we can expect from western Antarctica alone will create something like 1.4 metres of sea level rise by the end of this century, a disaster for coastal areas.
This expedition has gone by quickly: as I write this, we are again lurching our way across the stormy Drake Passage, back toward Argentina. But the educational program is ongoing, for those who can still stagger their way into the slanting lecture room. This morning we heard from our oceanographer, McGill’s Eric Galbraith, on climate change. He emphasized the reciprocal relationship between the global climate and that of Antarctica: not only is the continent enduringly affected by what goes on in the rest of the world, but it in turn plays a strong determining role in everything from global sea levels to the ocean’s ability to hold onto carbon. The hope of Students On Ice, the expedition’s organizers, is that even as we leave the continent behind us we’ll continue to remind ourselves and others of how closely tied together are its fate and our own.
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