The scientists made the observations this fall during an oceanographic cruise aboard a Russian icebreaker as part of the Nansen and Amundsen Basins Observational Systems (NABOS) program. During the last decade the program, along with other research, has shown a steady increase in the movement of warm water into the Arctic Ocean. The readings from this year show unprecedented warmth in some areas, the researchers said.
"The large area of the Arctic Ocean promises to become much warmer," said Igor Polyakov, NABOS principal investigator and a research professor at IARC.
Melting sea ice
The readings come from observational moorings, which are instrument-bearing buoys that are anchored to the ocean floor and float below the surface of the ocean.
The instruments first detected a surge of abnormal warm water, at mid-ocean depths of about 150 to 800 metres below the surface in February 2004 on the continental slope of the Laptev Sea, north of Siberia.
Sea ice is disappearing in the Arctic Ocean at unprecedented rates.
(Photo courtesy Arctic Coring Expedition)
That finding indicates that the warm water is moving further and further into the Arctic, Polyakov said, a trend that could increase the overall temperature of the Arctic Ocean.
The researchers note that the causes of the influx of warm water will require further study, but say the observations suggest that the Arctic Ocean is moving toward a warmer state, a change that could have global implications.
Ocean temperature in the Arctic is important because it may affect the amount of sea ice in the region. Scientists believe that Arctic sea ice cover plays a major role in the global climate, as ice reflects more of the sun's heat than open water.
Recent research has shown dramatic increases in Arctic sea ice melt, but has also shown that the average temperature of the upper oceans has cooled significantly since 2003. But the findings are not as contradictory as they might seem.
The study of ocean temperatures, released last week, "suggests global warming isn't always steady but happens with occasional 'speed bumps'," said coauthor Josh Willis, a scientist at NASA's Jet Propulsion Laboratory.
"This cooling is probably natural climate variability," Willis said. "The oceans today are still warmer than they were during the 1980s, and most scientists expect the oceans will eventually continue to warm in response to human-induced climate change."
The study found that the average temperature in the upper 2,500 feet of Earth's oceans - an area that represents about 20 percent of the global ocean's average depth - fell 0.055 degrees Fahrenheit from 2003 to 2005.
The recent decrease is a dip equal to about one-fifth of the heat gained by the ocean between 1955 and 2003, but the decline is a fraction of the total ocean warming seen over the previous 48 years, according to the study.
The findings have significant implications for global sea-level rise, Willis added.
Average sea level goes up partly due to warming and thermal expansion of the oceans and partly due to runoff from melting glaciers and ice sheets, he explained, and the recent cooling episode suggests that sea level should have actually decreased in the past two years.
"Despite this, sea level has continued to rise," Willis said. "This may mean that sea level rise has recently shifted from being mostly caused by warming to being dominated by melting. This idea is consistent with recent estimates of ice-mass loss in Antarctica and accelerating ice-mass loss on Greenland."
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