Informant38

One of Siberia's largest rivers is dumping about 10% more fresh water into the Arctic today than it was some 60 years ago, thanks to the complex effects of increased snowfall, melting permafrost and changing weather.
The result is in line with predictions of how climate change is expected to alter the Arctic water cycle, and is a worrying sign in terms of maintaining important ocean currents. The more fresh water that enters the northern seas, the less dense this water becomes and the less likely it is to sink. This sinking currently helps to drive a powerful Atlantic current that keeps the climate temperate and steady.
Freshening of the Arctic Ocean may already have begun to affect this so-called thermohaline circulation, but oceanographers and climate modellers are still puzzling about the magnitude and likely effects of the changes.

Quirin Schiermeier/Nature 06.Apr.06
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thermohaline circulation at Wikipedia
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Real Climate on Nature on the state of the science with regards to possible changes in the ocean thermohaline circulation in the Atlantic and its impact on climate.