This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers from Cornell University have pinpointed the source of oxygen that sustains deep-sea life in the North Atlantic Ocean: the churning waters in the Labrador Sea. The study, published in Nature Geoscience on Aug. 17, gives heightened significance to the Labrador Sea, sandwiched between Greenland and Newfoundland.
There, waters from the Atlantic Meridional Overturning Circulation (AMOC), the ocean's major current system, turn in a gyre, and oxygen-rich surface waters mix with deeper waters. Previous research had found that the Labrador Sea has little impact on the strength of AMOC, but the study finds it plays a critical role in oxygen transport. The research also sheds light on processes that may be helping the North Atlantic maintain its oxygen levels as oxygen declines in oceans globally because of warming temperatures.
"We found that the Labrador Sea exports enough oxygen to meet the biological need across a vast part of the deep North Atlantic Ocean, so it's very likely crucial to sustain these deep-sea ecosystems," said first author Una Miller, assistant professor of earth and atmospheric sciences. "Our finding shows that if we're going to understand the future, especially in the face of these deoxygenation trends, you can't just look at the strength of AMOC, you also have to understand processes in the Labrador Sea." The study comes amid debate about the vulnerability of AMOC, as the current has weakened over the past 75 years. AMOC carries warm water from the tropics to the North Atlantic and carbon dioxide and oxygen throughout the deep sea; the movement of warmer waters results in a more temperate Europe, and the gases sustain life and store carbon.
Scientists have warned that a collapse of the system could cause major disruption in weather and devastate ecosystems. Miller, working with a large team, used data from 60 oxygen sensors attached for the first time to moorings that run along the bottom of the Labrador and western Irminger seas. "No one's successfully sustained multiple years of oxygen measurements on moorings like these before, so that was one breakthrough, along with a machine learning method to fill in gaps so we could map these oxygen values," Palter said.
"Now we know the rate of oxygenation, we know the processes, and we can link it with other work to show that the current needs to take this last step in the Labrador Sea in order for ecosystems to function." Oxygen is hard to come by in the deep ocean, Palter said. Layers of ocean water, at different temperatures and densities, largely don't mix—she described the Atlantic as having a lid on it, which means oxygen entering from the air largely stays in the surface layer. But when currents circulate into the subpolar North Atlantic and the Labrador Sea, they become colder and denser—and they sink, carrying oxygen and carbon.
"That becomes the lower limb of AMOC, which spreads through the deep interior of the Atlantic Ocean," Miller said. "In terms of gases, that's really important, because there's no photosynthesis below a certain depth—the only atmospheric oxygen in the deep ocean is really from this overturning circulation, this injection of waters that were at the surface and flowed through the Labrador Sea." The researchers were able to quantify the amount of oxygen the Labrador Sea waters carry: more than 27 teramoles per year, enough oxygen to sustain breathing for every person on earth for at least two months. The team found that the amount of oxygen matches estimates of the respiration rates of microbes and animals across the North Atlantic deep sea.
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