The water is mostly coming from melting permafrost and rising rainfall, which is increasing flows in Siberian rivers that drain into the Arctic, such as the Ob and Yenisei. More comes from melting sea ice, says Laura de Steur of the Royal Netherlands Institute of Sea Research in 't Horntje, who is tracking the build-up.
Salinity anomalies like this are a regular feature of the Arctic. The last major event occurred in the 1960s. They happen when strong winds circling the Arctic restrict southward water movement. Eventually, the winds falter and the water flushes into the Atlantic through the Fram strait, between Greenland and Europe.
Recent Arctic melting runs the risk of increasing the freshwater build-up, potentially making the consequences of the eventual breakout more extreme, says de Steur. This is the first time that scientists have measured a salinity anomaly in the Arctic in detail, and in time to analyse how the freshwater pool breaks out into the North Atlantic.
De Steur believes the consequences could be more dramatic than in the past, because of how global warming is changing the dynamics of the region. "Sea ice is melting quicker. It is thinner and more mobile, and could exit the Arctic faster. Also more of it will enter the Atlantic as liquid water rather than ice." (read more)