The Labrador Sea, located in the North Atlantic Ocean between Greenland and Canada, is one of the few regions on our planet where oxygen from the atmosphere can reach the deep ocean directly, through “wintertime deep convection.” This is a process that homogenizes the water column to a depth of up to two kilometers and brings deep water undersaturated in oxygen in direct contact with the atmosphere.
A new study Dalhousie University in Halifax, Canada and the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany has measured the flow of oxygen into the ocean interior that is carried by deep currents in the Labrador Sea, and analyzed how this intense oxygen uptake affects the properties of the outflowing deep western boundary current, which distributes oxygen to the rest of the Atlantic Ocean and beyond.
According to the scientists, oxygen that is “inhaled” in the Labrador Sea can support deep ocean life in Antarctica and even as far as the Pacific or Indian oceans.
By using dissolved oxygen sensors mounted for two years on anchored cables that reached from near the surface to the seafloor, the researchers investigated the connection between oxygen uptake from the atmosphere and its onward transport into the interior of the oceans.
The analysis revealed that nearly half of the oxygen taken up from the atmosphere in the central Labrador Sea in winter was injected into the deep boundary current during the following five months, and distributed at vast distances.
“We wanted to know how much of the oxygen that is breathed in each winter actually makes it into the deep, fast-flowing currents that transport it across the globe,” said study lead author Jannes Koelling, an oceanographer at Dalhousie University.
“The circulation of the Labrador Sea is complex, and we’ve only focused, so far, on the most direct export route. Some oxygen-rich water may be transported eastwards, instead of to the southwest, and it may enter the boundary current off Greenland before returning southwards, over a longer time-period.”
Better understanding the pathways through which oxygen flows from the “lung of the deep ocean,” as the Labrador Sea is known, to other seas and oceans is of utmost importance in our climate change era.
Since climate model projections suggest that an increased supply of freshwater from melting glaciers and other climate-related changes in the Arctic could reduce the depth of wintertime mixing in the Labrador Sea in the next decades, and thus affect the life-supporting supply of oxygen to the deep sea, close monitoring of these changes is essential in order to mitigate the effects of anthropogenic global warming on a variety of ecosystems.
The study is published in the journal Biogeosciences.