Polar bear images via Dave Hogg and ucumari on Flickr

Scientists believe that polar bears are having to swim greater distances to search for Arctic sea ice. Polar bears rely on sea ice to hunt for seals. However, their icy habitat is disappearing due to anthropogenic climate change. Scientists from the U.S. Geological Survey tracked a polar bear and determined that it swam continuously for over nine days. More via the BBC:

Scientists studying bears around the Beaufort sea, north of Alaska, claim this endurance feat could be a result of climate change.

Polar bears are known to swim between land and sea ice floes to hunt seals.

But the researchers say that increased sea ice melts push polar bears to swim greater distances, risking their own health and future generations.

.       .       .

“This bear swam continuously for 232 hours and 687 km and through waters that were 2-6 degrees C,” says research zoologist George M. Durner.

“We are in awe that an animal that spends most of its time on the surface of sea ice could swim constantly for so long in water so cold. It is truly an amazing feat.”

Although bears have been observed in open water in the past, this is the first time one’s entire journey has been followed.

By fitting a GPS collar to a female bear, researchers were able to accurately plot its movements for two months as it sought out hunting grounds.

The scientists were able to determine when the bear was in the water by the collar data and a temperature logger implanted beneath the bear’s skin.

The study shows that this epic journey came at a very high cost to the bear.

“This individual lost 22% of her body fat in two months and her yearling cub,” says Mr Durner.
“It was simply more energetically costly for the yearling than the adult to make this long distance swim,” he explains.

Arctic sea ice is expected to continue to decline. The Washington Post reports that “the U.S. military anticipates the Arctic will become ‘ice-free’ for several summer weeks by 2030, possibly as early as 2013.” Furthermore, according to the National Snow and Ice Data Center, “Arctic sea ice extent for December 2010 was the lowest in the satellite record for that month. These low ice conditions are linked to a strong negative phase of the Arctic Oscillation.” In addition to climate change, the Arctic Oscillation also has an effect on Arctic sea ice extent. According to NASA, the Arctic Oscillation “likely triggered a phase of accelerated melt that continued into the next decade thanks to unusually warm Arctic air temperatures.” More on the Arctic Oscillation via NASA:

The overall configuration of warmer-than-normal temperatures in the north and cooler-than-normal temperatures in the south probably results from a climate pattern known as the Arctic Oscillation (AO).

The AO is a pattern of differences in air pressure between the Arctic and mid-latitudes. When the AO is in “positive” phase, air pressure over the Arctic is low, pressure over the mid-latitudes is high, and prevailing winds confine extremely cold air to the Arctic. But when the AO is in “negative” phase, the pressure gradient weakens. The air pressure over the Arctic is not quite so low, and air pressure at mid-latitudes is not as high. In this negative phase, the AO enables Arctic air to slide south and warm air to slip north.

The AO went into negative phase in the Northern Hemisphere winter of 2009–2010. The AO was in negative mode again in the winter of 2010–2011, affecting temperatures across the Northern Hemisphere as early as December 2010.

More from NASA on the Arctic Oscillation and on the impacts of Arctic sea ice loss:

Natural variability and rising temperatures linked to global warming both appear to have played a role in this decline. The Arctic Oscillation’s strongly positive mode through the mid-1990s flushed thicker, older ice out of the Arctic, replacing multiyear ice with first-year ice that is more prone to melting. After the mid-1990s, the AO assumed a more neutral phase, but sea ice failed to recover. Instead, a pattern of steep Arctic sea ice decline began in 2002. The AO likely triggered a phase of accelerated melt that continued into the next decade thanks to unusually warm Arctic air temperatures.

.       .       .

Projected effects of declining sea ice include loss of habitat for seals and polar bears, as well as movement of polar bears onto land where bear-human encounters may increase. Indigenous peoples in the Arctic who rely on Arctic animals for food have already described changes in the health and numbers of polar bears.

As sea ice retreats from coastlines, wind-driven waves—combined with permafrost thaw—can lead to rapid coastal erosion. Alaskan and Siberian coastlines have already experienced coastal erosion.

Other potential impacts of Arctic sea ice loss include changed weather patterns: less precipitation in the American West, a weaker storm track that has shifted south over the Atlantic, or (according to one simulation) an intensified storm track.

Some researchers have hypothesized that melting sea ice could interfere with ocean circulation. In the Arctic, ocean circulation is driven by the sinking of dense, salty water. A cap of freshwater resulting from rapid, extensive sea ice melt could interfere with ocean circulation at high latitudes. Although a study published in 2005 suggested that the Atlantic meridional (north-south) overturning circulation had slowed by about 30 percent between 1957 and 2004, that conclusion was not based on comprehensive measurements. Subsequent modeling analyses indicated that the freshwater from melting sea ice was not likely to affect ocean circulation for decades.

Recently, a study determined “that water flowing from the Atlantic Ocean into the Arctic is warmer than it’s been in 2,000 years.” Via the Montreal Gazette:

Annual average air temperatures have climbed almost three degrees Celsius at the Eureka weather station in the Canada’s High Arctic since 1972, a trend seen across much of the North, which is breaking records again this winter. In December sea ice extent was the lowest on record since 1979, and temperatures were above average in much of the Arctic.

To understand what is happening scientists say they need a better read on the long-term natural variation in the currents flowing north.

Few records go back more than 150 years, so Spielhagen’s team pulled up sediments up from the sea floor, which contain the remains of organisms that have been living and dying in the water over the eons. By studying the tiny-shelled organisms called foraminifera, which grow best under specific conditions, they could chart temperatures going back 2,000 years.

Their sampling site was 1,500 metres below the water surface and under the path of Atlantic water flowing to the Arctic Ocean.

They report the water has warmed about 2 C since late 1800s. The top couple of centimetres of sediment, representing the last 10 to 20 years, corresponds with a summer temperature of 6 C, which matches what is now seen in the northbound current.

The scientists say the data indicates that the modern warming is not just the latest natural variation or swing.

.       .       .

He and his colleagues conclude the warm water flowing north is “most likely another key element in the transition toward” an Arctic that will eventually see sea ice melt away every summer.

Image via USGS