Labrador Sea identified as primary oxygen source for deep North Atlantic ecosystems

Researchers from Cornell University have determined that the Labrador Sea is the critical source of oxygen sustaining deep-sea ecosystems across a vast portion of the North Atlantic Ocean. The study, published in Nature Geoscience on August 17, used data from 60 oxygen sensors deployed on moorings along the bottom of the Labrador and western Irminger seas from 2020 to 2022. This array provided the first successful multi-year oxygen measurements on such moorings, combined with a machine-learning method to fill data gaps and map oxygen values.

The team quantified the oxygen transport at more than 27 teramoles per year, a volume sufficient to meet the estimated respiration rates of microbes and animals throughout the deep North Atlantic. Lead author Una Miller, assistant professor of earth and atmospheric sciences, stated that the Labrador Sea exports enough oxygen to meet biological demand across this region, making it crucial for sustaining these ecosystems. Co-author Jaime Palter noted that oxygen is scarce in the deep ocean because density layers typically prevent mixing, but in the Labrador Sea, surface waters become colder and denser, sink, and carry atmospheric oxygen into the deep limb of the Atlantic Meridional Overturning Circulation (AMOC).

Previous research had indicated the Labrador Sea has little impact on the strength of AMOC, the major current system that transports heat and gases. However, this study distinguishes the sea's role in oxygen transport from its role in circulation strength. The findings show that the final step of convection in the Labrador Sea is necessary for the current to deliver oxygen to deep-sea life, even if AMOC's overall vigor changes. The correlation between the measured oxygen supply and estimated deep-sea respiration rates strongly suggests that deep-sea life relies on this specific regional process, one of the few areas where such deep mixing occurs.

The research comes amid scientific debate about AMOC's vulnerability, as the circulation has weakened over the past 75 years. Scientists have warned that a collapse could disrupt weather patterns and devastate ecosystems. Miller emphasized that understanding future deoxygenation trends requires looking beyond AMOC strength to the specific processes in the Labrador Sea. The team faced significant technical challenges, leaving sensors in the harsh deep-sea environment for two years without certainty of survival, followed by a multi-year effort to process the messy data.

Open questions remain regarding the relationship between AMOC strength and oxygenation processes, and how weakening of one or both would affect deep-sea ecosystems. Miller is continuing research on oxygenation in the Southern Ocean around Antarctica, another critical region where surface waters connect to the deep ocean. The study underscores that the Labrador Sea functions as a distinct oxygen pipeline, balancing consumption across much of the deep North Atlantic and supporting life that suffers when oxygen dips below critical thresholds.