Monday, February 14, 2011

Warm ocean current temperatures traced to Fram Strait in Arctic

Using as tiny climate sensors the miniscule bodies of hard-shelled protozoa deposited on the sea floor over millennia, an international research team has made a startling discovery off the coast of Greenland.
A northbound current flowing far beneath the surface of the Atlantic Ocean through Fram Strait has been sloshing the warmest water of the past 2,000 years into the Arctic Ocean -- indirectly contributing to the thinning and shrinkage of sea ice near Alaska and across the Arctic.
This unprecedented flow, almost 3.6 degrees Fahrenheit warmer than when Augustus ruled Rome, has now become a key factor in the decades-long shift toward ice-free summers in the Arctic, as its heat spreads out and slowly mixes with colder waters at the surface, according to a new study published recently in the journal Science.
"We find that early-21st-century temperatures of Atlantic water entering the Arctic Ocean are unprecedented over the past 2,000 years and are presumably linked to the Arctic amplification of global warming," wrote lead investigator Robert Spielhagen, a palaeoceanographer at the Leibniz Institute of Marine Sciences in Kiel, Germany, along with eight coauthors from Colorado, Germany and Norway.
The most stunning increase in the current occurred over the last 120 years, the scientists said, coinciding with other indicators of human-triggered climate change. This particular stream of water is now about 2.5 degrees-F warmer than it was during the so-called Medieval Warm Period between 900 and 1300, when Vikings planted crops in Greenland and vineyards supposedly spread across southern England.
"Such a warming of the Atlantic water in the Fram Strait is significantly different from all climate variations in the last 2,000 years," Spielhagen said in a story posted by the University of Colorado about the study.
"We know that the Arctic is the most sensitive region on the Earth when it comes to warming, but there has been some question about how unusual the current Arctic warming is compared to the natural variability of the last thousand years," added study co-author Thomas Marchitto, a fellow at CU-Boulder's Institute of Arctic and Alpine Research, in the same story. "We found that modern Fram Strait water temperatures are well outside the natural bounds."
But how could these paleo-scientists figure out the temperature of an ocean current that was flowing beneath the surface in the year 1066 -- or any other time in the pre-modern past? Since weather and oceanographic measurements for Fram Strait date back only about 150 years, the scientists had to reach deep for their data. Literally.
In 2007, the team traveled in the German research vessel Maria S. Merian to a location between the Spitsbergen archipelago and Greenland in the direct path of the current and retrieved an 18-inch sample of sediment from the ocean floor that had been deposited over the past 2,000 years.
Each one-fifth inch slice of muck opened a window that looked a couple of decades deeper into the past.
Contained within these layers of compressed history were the microscopic bodies of a kind of plankton called foraminifer -- a creature that lives, dies and falls to the sea bottom by the uncounted billions in a constant organic rain year after year.
Different species of foraminifer proliferate at different temperatures; some like it very cold, others like it somewhat warmer. By comparing the proportions of each type, the scientists could get a pretty good estimate of the ocean temperature when they were alive. Another indicator was the ratio of magnesium to calcium in their shells.
The results suggest that summer water temperatures in the current averaged around 38 degrees-F from AD 1 until the 1850s, when they suddenly shot higher, ultimately warming to more than 41-degrees F.
"The timing suggests that manmade climate change is the cause of the warming, the authors say," according to a Nature News story about the study.
Oceanographer Joshua Willis of the Jet Propulsion Laboratory in Pasadena, Calif., told Nature News that the results were "another hockey stick" -- similar to the controversial hockey stick-shaped graph that shows a spike up in air temperatures in this century.
The current through Fram Srait is one element in the region's "ocean conveyor belt" that delivers heat from the Gulf Stream and parts south, up the Atlantic and into the Arctic. It's one factor that keeps areas near Svalbard ice-free all winter.
More heat ultimately means more melt.
"Cold seawater is critical for the formation of sea ice, which helps to cool the planet by reflecting sunlight back to space," Marchitto said. "Sea ice also allows Arctic air temperatures to be very cold by forming an insulating blanket over the ocean. Warmer waters could lead to major sea ice loss and drastic changes for the Arctic."
The study has garnered international attention withdozens of news sites carrying stories about the results. Many of the stories linked the findings to record air temperatures seen this winter in eastern Canada and Greenland, and noted that sea ice covered the third-smallest area on record as of December partly as a result.
"We must assume that the accelerated decrease of the Arctic sea ice cover and the warming of the ocean and atmosphere of the Arctic measured in recent decades are in part related to an increased heat transfer from the Atlantic," according to Spielhagen.
"It doesn't necessarily prove that the change that we see is man-made, but it does strongly point toward this being an unusual event," Marchitto told the New York Times Green blog. "On a scale of 2,000 years, it stands out dramatically as something that does not look natural."

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Export of pacific carbon through the arctic archipelago to the North Atlantic

E.H. ShadwickaCorresponding Author Contact InformationE-mail The Corresponding Author, H. Thomasa, Y. Grattonb, D. Leonga, S.A. Moorea, T. Papakyriakouc and A.E.F. Proweabcd
a Department of Oceanography, Dalhousie University, Halifax NS, Canada
b Institut National de Recherche Scientifique, Centre Eau, Terre et Environnement, Québec, QC, Canada
c Center for Earth Observation Science, University of Manitoba, Winnipeg MB, Canada
d Leibniz-Institut für Meereswissenschaften, IFM-GEOMAR, D-24105 Kiel, Germany
Received 11 March 2010;  
revised 20 January 2011;  
accepted 31 January 2011.  
Available online 5 February 2011. 


During an east-to-west transect through the Canadian Arctic Archipelago, dissolved inorganic carbon (DIC) and total alkalinity (TA) were measured. The composition of the waters throughout the Archipelago were computed using TA and δ18O data, and the carbon characteristics of these waters is examined. The influence of the Mackenzie River is primarily limited to the upper water column in the western Archipelago while the fraction of sea-ice melt water in the surface waters increases eastward with maximum values at the outflows of Jones and Lancaster Sounds. The depth of penetration of Pacific-origin upper halocline waters increases eastward through the Archipelago. In the western Archipelago, non-conservative variations in deep water DIC are used to compute a subsurface carbon surplus, which appears to be fueled by organic matter produced in the surface layer and by benthic respiration. The eastward transport of carbon from the Pacific, via the Arctic Archipelago, to the North Atlantic is estimated. The impact of increased export of sea-ice melt water to the North Atlantic is also discussed.

Research Highlights

► inorganic carbon data from eastwest transect in Arctic Archipelago. ► water mass composition determined with TA, S and d18O. ► fraction of seaice melt water increases eastward though Archipelago. ► nonconservative variations in DIC indicate subsurface carbon surplus. ► eastward transport of carbon from Pacific to Atlantic estimated.
Keywords: Arctic Archipelago, Inorganic Carbon System, International Polar Year (IPY)

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