Canadian and German scientists say they have measured the flow of oxygen in and out of the deep ocean in the Labrador Sea for the first time, providing new insight into what has been called “a lung of the ocean” that is vital for keeping marine life alive.
The Labrador Sea is one of the few places where oxygen from the atmosphere is transferred to the deepest parts of the ocean and distributed throughout the Atlantic and eventually into the Pacific and Indian Oceans.
“Without this transport of oxygen by the equivalent of our bloodstream there would be no animal life, there would be microbial life, but no animal life in the deep ocean,” says Doug Wallace, an oceanography professor at Dalhousie University in Halifax.
“It’s absolutely essential for the deep ocean ecosystems.”
How the ocean lung works
Wintertime cooling in the Labrador Sea makes oxygen-rich surface waters denser and heavy enough to sink to a depth of two kilometres where the oxygen is dispersed by deep boundary currents.
Using sensors moored between Labrador and Greenland, researchers measured the flow of oxygen into the deep ocean interior over a two-year period.
The sensors were deployed at a depth of 600 metres from cables anchored to the ocean floor.
They were located along an array at 53 degrees north latitude where scientists expected deep mixing in the centre of the Labrador Sea to spread into the Atlantic.
Half the oxygen exhaled into deep ocean currents
About half of the “inhaled” oxygen was injected into deep water currents over a five month period.
“The timing was a surprise actually for us because I think we imagined it would be just spread out over the whole year. But what we see was a very distinct pulse of oxygen for a few months only and then things went back to background,” says Wallace, who co-authored a paper on the research published in the journal Biogeosciences.
The research was a collaboration between the Ocean Frontier Institute, based at Dalhousie University in Halifax and the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany.
“This study is an example of how monitoring enabled by the latest ocean technology can help us fill in knowledge gaps in this important region,” says Dariia Atamanchuk, who leads the oxygen program at Dalhousie
“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. The newly inhaled oxygen was clearly noticeable as a pulse of high oxygen concentration that passed our sensors between March and August,” lead author James Koelling said in a statement.
More sensor results expected
In the meantime, more sensors have been deployed in the Labrador Sea closer to western Greenland.
The research is a part of an international effort involving scientists from Canada, the United States and Europe.
When the sensors start coming out of the water as soon as this year, researchers will have a more complete picture of the way oxygen flows within the region.
A window on climate change
Scientists also say this monitoring of oxygen flow can help understand the effects of climate change.
Modelling suggests lighter, freshwater from melting glaciers does not sink as readily and that could reduce deep water mixing.
“So in effect, there’s a risk and I’m saying it’s a risk that the breathing of the ocean in that region could become shallower… and the transport of oxygen into the deep ocean and therefore into this bloodstream will become less. So that’s why we think it’s really important to measure it,” says Wallace.
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