The freshwater content of the upper Arctic Ocean has increased by about 20% since the 1990s, according to a new large-scale assessment.
This corresponds to a staggering rise of around 8,400 cubic kilometres of extra water, much of which will flow into the North Atlantic, therefore threatening the temperature balance that currently enables the UK to enjoy a relatively mild climate.
Around 10% of the global mainland run-off flows into the Arctic, via the enormous Siberian and North American rivers, in addition to relatively low-salt water from the Pacific.
This freshwater lies as a light layer on top of the deeper salty and warm ocean layers, and extensively cuts off heat flow to the ice and atmosphere.
Changes in this layer are therefore major control parameters for the sensitive heat balance of the ever-changing Arctic.
We can expect that the additional amount of freshwater in the near-surface layer of the Arctic Ocean will flow out into the North Atlantic in the coming years.
The amount of freshwater flowing out of the Arctic influences the formation of deep water in the Greenland Sea and Labrador Sea, and has impacts on global ocean circulation.
Dr Benjamin Rabe from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association and his colleagues have examined and evaluated a total of more than 5,000 measured salt concentration profiles.
“The considerable changes in the upper water layers primarily comprise a decline in salt concentration,” said Dr Rabe.
Dr Michael Karcher from the Alfred Wegener Institute has simulated the observed processes using a sophisticated ocean/sea ice model.
The model experiments make it possible to study longer periods, that is to effectively map times for which no measurement data is currently available.
The model also supplies important insights into the causes of the rising and falling freshwater content, and points out the great significance of the local wind field.
Measurements and the model also show that the changes in the Arctic freshwater content encompass far larger areas than assumed to date. Some years ago, Scottish fisheries research vessel Scotia identified worrying changes to North Atlantic currents and temperature profiles.
The Arctic data is certain to add to growing worries over the future climate of Northern Europe, including the UK.