"Large regions of the North Atlantic Ocean have been growing fresher since the late 1960s as melting glaciers and increased precipitation, both associated with greenhouse warming, have enhanced continental runoff into the Arctic and sub-Arctic seas. Over the same time period, salinity records show that large pulses of extra sea ice and fresh water from the Arctic have flowed into the North Atlantic. But, until now, the actual amounts and rates of fresh water accumulation have not been explicitly known.
In a paper to be published June 17 in Science, Ruth Curry of the Woods Hole Oceanographic Institution (WHOI) and Cecilie Mauritzen of the Norwegian Meteorological Institute quantified for the first time how much additional fresh water caused the observed salinity changes in the northern North Atlantic Ocean, how fast it entered the Atlantic circulation, and where that fresh water was stored.
They report that patterns of fresh water accumulation over the past four decades suggest that a freshening threshold important to the ocean circulation and its poleward transport of heat could be reached in a century, although future impacts of global warming and glacial melting make prediction imprecise at this time. Curry, a research specialist in the WHOI Physical Oceanography Department, and Mauritzen, an oceanographer at the Norwegian Meteorological Institute, analysed data collected in the North Atlantic Ocean between Labrador, Greenland and northern Europe over the last 55 years to reconstruct the history of ocean properties such as temperature, salinity and density.
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In an average year, about 5000 cubic kilometers (km) of fresh water flows from the Arctic into the North Atlantic through passages located east and west of Greenland. The researchers estimate that in addition to this amount, an extra 19,000 cubic km flowed into and diluted the northern seas over the 30-yea time period between 1965 and 1995. Fully half of the excess fresh water (~10,000 cubic km) entered the system in the late 1960s boosting the flow rate from 5000 to ~7000 cubic km per year-a 40% increase in fresh water inflow. For comparison, the outflow from the Mississippi River each year is about 500 cubic km, while Earth’s largest river, the Amazon, discharges 5000-6000 cubic km annually."
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http://www.terradaily.com/news/oceans-05h.html