Nares Strait

To understand why knowledge of the freshwater flux through Nares Strait is so important, we need to take a step back and put the Nares Strait in the bigger perspective of a global ocean circulation, which is considered to play a vital role in our climate system. This circulation, known to oceanographers as the “thermohaline circulation”, carries warm water (in the order of one petawatt!) in the surface layer from the southern hemisphere to the North Atlantic Ocean, where heat from the water is taken up by the prevailing westerly winds and brought to Europe. This is why the winters in western Europe are relatively mild compared to, for example, regions in eastern Canada that share the same latitude. The ocean water continues to flow northwards until it reaches the semi-enclosed basins in the northern North Atlantic Ocean. There, during the coldest winter months very strong and cold winds increase the density of the water in the surface layer until it mixes with the dense water at greater depth. The now very cold water returns to the southern hemisphere in the deep ocean.

One of the vital links in this circulation is the ability of the winter atmospheric conditions to increase the density of the surface waters in the northern North Atlantic Ocean. The density of sea water depends on its temperature (colder water is denser) and its salinity (more saline water is denser). Therefore, if the surface water is relatively fresh it is less likely that deep mixing will occur and that would slow the circulation down (which will likely have a large effect on the west-European climate). One of the main sources of fresh water to the North Atlantic Ocean is freshwater from the Arctic, both as a liquid and in the form of sea ice. This freshwater can enter on the east side of Greenland through Fram Strait, or on the west side of Greenland through the Canadian Arctic Archipelago, where at least a significant part of the freshwater makes its way to the Atlantic Ocean through Nares Strait.

Apart from its role in the climate system, the Nares Strait also contains a polynya with a higher biological productivity than almost anywhere else in the northern hemisphere. Furthermore, the exported ice migrates to the western part of Baffin Bay and southwards towards Newfoundland. If it continues to be thick, multi-year ice, it could impede opening up of the Northwest Passage for shipping. Also, as a key exit route for Arctic Sea ice knowledge about ice flow through Nares Strait is very important for the Arctic ice budget.

Our knowledge of the flow through this Strait is, however, very limited. Thanks to intense measuring campaigns since 2003, we are starting to get some idea of the total freshwater flow, the flow structure and the ice conditions in this part of the ocean. Things we still do not know are what determines the throughflow, on which time scales we can expect natural variability in both ice conditions and freshwater throughflow, and, not unimportant, how large the freshwater content of the upper 30 meters is as we cannot measure this part of the water column with moorings (they would be destroyed by the ice). The measuring campaign this summer will hopefully add three more years of measurements and several summer snapshots. To fully understand the physical processes that drive the flow, however, taking measurements will not be sufficient. To this end computer models are used for this area, validated against the observations taken on site, which enable different combinations of potentially important factors to be studied. The first results of these studies are expected over the next couple of years!