New study says impacts expected to show up in 20-30 years
Ocean researchers tracking currents in the North Atlantic say that, so far, the massive amounts of freshwater, pouring off the melting Greenland Ice Sheet haven’t yet had a major effect on the Gulf Stream.
That influx of fresh water has increased by 50 percent since 1990 from both enhanced summer melt and calving outlet glaciers that are adding about 5,000 cubic kilometers of water per year — equivalent to a quarter of the volume of the Baltic Sea.
But much of that water isn’t staying where it will affect the Gulf Stream, at least for now. According to the study by an international team of scientists led by the GEOMAR Helmholtz Centre for Ocean Research Kiel, swift currents along the coast of North America are flushing the water southward.
“Thus changes in the critical, northern seas are delayed”, said GEOMAR Prof. Claus Böning, lead author of the study.
The fate of the melt water is of great interest because the Gulf Stream, which transports warm water from the tropics northward, is governed by the density of the waters surrounding Greenland. If the cold water changes the balance in the Labrador Sea area, it could ultimately lead to a weakening of the Gulf Stream.
The effects of the melting Greenland glaciers initially remain smaller than expected the researchers found after using a new computer model to simulate the pathways and effects of the additional meltwater. The model takes into account the regional differences in meltwater discharge trends and very fine details of the ocean currents, which allowed the researchers to assess the influences of the narrow boundary currents and small-scale eddies on the water exchange between the coastal shelf and the deep ocean.
The model showed that more than half of the meltwater is transported southwards along the Canadian coast by the Labrador Current. Less than 20 percent remain in the area between Greenland and Labrador which is critical for the Gulf Stream system. The model suggests that the melting-induced impact on ocean salinity is, to date, only half as large as natural variations measured in the past decades.
However, the simulation also shows a progressive trend in the freshening of the Labrador Sea.
“If we project the rise in Greenland melting rates into the future, we expect first noticeable changes in the Labrador Sea in two or three decades”, said Professor Böning, “in this sense the Gulf Stream may just get some breathing space.”
“Meltwater fluxes from Greenland have been accelerating in recent years and if, as seems likely, this trend continues we could see changes in ocean circulation even sooner,” said co-author Jonathan Bamber, Professor at the University of Bristol.