Labrador Sea using bubbles, marine trap door to help the ocean breathe

The Labrador Sea in the North Atlantic is known as one of the lungs of the ocean, absorbing vast quantities of oxygen that sink up to two kilometres and then flow slowly around the world.

It turns out the Labrador Sea is taking a much bigger breath than anyone realized.

New research from Canadian and American scientists estimates the ocean between Labrador and Greenland is absorbing up to 10 times more oxygen than previous climate models predicted.

The oxygen is being transferred through a seasonal "trap door" that opens in winter and injects air bubbles created in winter storms.

Research shows that 60 per cent of dissolved oxygen sinks during the 40-day winter window.

Researchers from Dalhousie University in Halifax and the Scripps Institution of Oceanography in California used an advanced sensor system that spent a year anchored to the bottom of the Labrador Sea taking chemical measurements in the water column.

"We found the transfer of gases and particular oxygen is much greater than we thought," said Dariia Atamanchuk, a research associate in Dalhousie's oceanography department and the lead author of a study containing the findings published this week in the journal Nature Geoscience.

"The reason for that is a transfer mediated by bubbles. What happens is the breaking waves create bubbles and these bubbles get trapped. And as water sinks, these bubbles are being basically drawn down to 2,000 metres."

The higher-than-expected intake of oxygen suggests fish and other organisms in the deep sea require more oxygen than previously thought, leaving the ecosystem more vulnerable to climate change.

Why oxygen transfer in Labrador Sea is vulnerable

The melting of Greenland and Arctic ice sheets will put more lighter freshwater into the Labrador Sea, impeding the oxygen transfer.

"The surface water is less dense. It's harder for it to sink to greater depths. It will sink, but it will sink shallower, so the breathing becomes shallower," Atamanchuk said.

It takes hundreds of years for deepwater formed in the Labrador Sea to to reach the North Pacific.

"There is no immediate threat even if the breathing will become shallow tomorrow," Atamanchuk said. "It is important that we get all these processes right and to predict what will happen in the future with the deep-sea ecosystems."

The key to the research was the May 2016 deployment of the SeaCycler from the Maria S Merian, a German research vessel.

The device, which cost $1 million, spent a year stationed in the Labrador Sea at a depth of 150 metres, where it deployed an instrument float that measured oxygen and carbon dioxide as it rose to the surface.

Every 20 hours, a separate communication float popped to the surface to transmit data to a satellite.

All three devices are connected by cable.

Multinational collaboration

The research is part of a Canadian-led project to study atmospheric gas exchange and deep convection within the Labrador Sea.

SeaCycler was originally developed by the Department of Fisheries and Oceans at the Bedford Institute of Oceanography, in conjunction with the Scripps Institution.

In addition to the vessel, the German marine research centre Geomar was also involved.

What happens next

Since it was removed from the ocean, SeaCycler has been overhauled with new electronics at Dalhousie and tested in the Bedford Basin.

It's going back to the Labrador Sea in September armed with a raft of new sensors that will measure zooplankton, nitrates, phosphates and take video images of underwater particles.

Atamanchuk said a second SeaCycler will be built at Dalhousie with support from the Ocean Frontier Institute and Canada, with a goal of establishing a permanent ocean observatory in the Labrador Sea.

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