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Palmer LTER scientists learn more about why region is heating up so dramatically
Posted March 28, 2008
Soon we may have to call it the Subantarctic Peninsula.
Scientists who monitor the ecosystem at the northern tip of the Antarctic Peninsula say a warmer, moist climate has migrated into their research area, virtually eliminating perennial sea ice there and driving the local Adélie penguin population to the brink of extinction.
“Our prediction now is that within the next five to 10 years there will not be any Adélies left at Palmer of any consequence,” said Bill Fraser, one of the principal investigators studying the ecosystem near Palmer Station, a U.S. research station located on Anvers Island off the coast of the peninsula.
The formal name of the ecosystem study is the Palmer Long Term Ecological Research (PAL LTER) program, a multi-disciplinary approach to understand the processes that affect climate and environmental change over a broad time scale. Established in 1990, the PAL LTER is part of a larger system of 26 LTER sites, mostly in and around the United States.
Researchers say the peninsula, particularly a 100,000-square-kilometer swath in the ocean that makes up the PAL LTER study site, is undergoing some of the most rapid climate change on the planet.
“It’s amazing what’s happening,” said Doug Martinson, another PAL LTER principal investigator. “It’s showing the most rapid rise in air temperature during winter time.”
The increase is about 6.5 degrees Celsius in the winter since the 1950s, rising more than five times faster than the global average. The life cycle of winter sea ice, on average, has dropped by three months per year, meaning it forms later and melts earlier. Year-round sea ice has virtually disappeared.
“We pretty much don’t have any perennial sea ice in our grid anymore, which has dramatic implications for the ecology and Bill Fraser’s penguins,” Martinson said. “That is just a staggering change in the sea ice distribution.”
It’s not only the atmosphere that’s heating up. Martinson, a senior research scientist with the Lamont-Doherty Earth Observatory at Columbia University, explained that air temperature alone doesn’t have enough heat capacity to cause the wholesale melting of glaciers in West Antarctica. “The real source of heat has to be the ocean,” he said.
Between their own observations and data from other researchers, the PAL LTER scientists believe an upwelling of warmer, deep ocean water is coming on to the continental shelf along the peninsula. The shelf is the extended perimeter of the continent below sea level, ending at a point of increasing slope called the shelf break.
In most of the world, deep ocean water is colder than surface water. But in Antarctica, where the surface water temperature of the Southern Ocean is slightly below freezing (salinity prevents it from turning to ice), this current of deeper seawater is about 3.5 to 4 degrees Celsius above zero.
Volume for volume, water has a tremendous heat capacity compared to air — more than 4,000 times greater, according to Martinson. “The bottom line is that it’s a humongous amount of heat,” he said.
Intensified westerly winds are causing the upwelling, but it’s the Antarctic Circumpolar Current (ACC) that pushes the warmer water onto the shallow shelf. The ACC is the dominant ocean current of the Southern Ocean. In a sense, it isolates Antarctica, helping preserve its ice sheets by serving as a kind of buffer against warmer surface water. The closest place where it knocks against the continent? You guessed it — the Antarctic Peninsula.
“The ACC … just sort of slams into the continental shelf right there off the peninsula, so it’s a place where there’s an enormous heat transfer,” said Hugh Ducklow, the lead investigator for the PAL LTER. “It’s pumping all of this ocean heat into our region.”
Or as physical oceanographer Martinson explained it: “It’s like having this freight train of hot coals skirt right along the Antarctic Peninsula, the whole length, right along the continental shelf.”
That train track, the ACC, runs west to east, charging by numerous glaciers that pour out of West Antarctica. A recent NASA-led study said that the rate of Antarctic ice loss increased by 75 percent in the last 10 years as glacier flow increased.
That study’s lead investigator, Eric Rignot of NASA’s Jet Propulsion Laboratory, speculated that the losses, concentrated in West Antarctica’s Pine Island Bay sector and the northern tip of the Antarctic Peninsula, are the result of warmer ocean waters, which “bathe the buttressing floating sections of glaciers, causing them to thin or collapse.” Martinson's LTER ocean data support that speculation.
Rignot also noted that last year’s report by the Intergovernmental Panel on Climate Change (IPCC) did not properly account for Antarctica’s role in sea level rise estimates. Rignot’s team estimated Antarctic ice loss is now nearly as great as that observed in Greenland. The 2007 IPCC report estimated that the global average sea level could rise between 18 and 59 centimeters in the next century.
“Sea level is going to rise much faster than [IPCC estimates],” Martinson cautioned.