Freshwater pouring into northern oceans is slowly turning high-latitude waters less salty.
Shrinking ice sheets and melting glaciers are partly responsible for the freshening effect and if salinity levels continue to drop, this could pose a threat to shipping particularly cargo vessels.
Fluctuating salinity could potentially result from a normal periodical weather pattern known as the North Atlantic Oscillation index. If this index is high, seas in the north are less salty than average.
Until 1995, the changes were in line with what would be expected under the climatic conditions; but when the index changed recently, becoming low or neutral, the proportion of fresh water did not go down accordingly in some places.
So the greater bulk of fresh water running into the sea is probably – at least in part – due to rising global temperatures.
Salt water is much denser and therefore more buoyant than fresh water and cargo vessels are designed to operate in salt water.
When fully laden they tend to lie quite low in the water, salt water that is. A fully laden cargo vessel entering an area of fresh water could find itself in real danger of sinking.
