Award: OCE-1947970

The subpolar North Atlantic Ocean plays a key role in ocean circulation. Here, cold, dense surface waters sink into the deep ocean, driving the long-term circulation of waters in the Atlantic, known as the Atlantic Meridional Overturning Circulation (AMOC). By transporting cold, fresh waters southward and warm, salty water northward, the AMOC strongly influences global climate. Therefore, considerable attention has been paid to monitoring the AMOC and the processes that drive it, as well as improving our understanding of how AMOC strength has changed over time and may change in the future.

The AMOC also plays an important role in enabling the ocean to absorb gases - in particular, oxygen and carbon dioxide - from the atmosphere. Prior to sinking into the deep ocean where they are isolated from contact with the atmosphere, the cold waters that spread throughout the deep North Atlantic are subject to vigorous mixing, driving gas uptake. This provides the oxygen that is respired by marine organisms as these water masses move through the ocean, and also enables these waters to absorb and store anthropogenic carbon. Understanding the controls on gas uptake in the subpolar North Atlantic is therefore important as we seek to monitor and predict ongoing ocean deoxygenation and its effects on marine ecosystems, as well as ocean acidification and carbon sequestration.

Prior research has systematically observed the strength and variability of the AMOC through moorings deployed across the subpolar North Atlantic Ocean. Observations collected by the Overturning in the Subpolar North Atlantic Program (OSNAP) beginning in 2014 have demonstrated that the majority of the strength and year-to-year variability of the AMOC is driven by the region east of Greenland, with the region west of Greenland, known at the Labrador Sea, playing a more minor role. However, our team hypothesized that the Labrador Sea might yet play an important role in the uptake of gases from the atmosphere due to partial decoupling of gas uptake from circulation. The Labrador Sea experiences extremely deep wintertime mixing within the surface layer of the ocean in contact with the atmosphere, which we hypothesized could enable this region to play a leading role in absorbing atmospheric gases.

To test this hypothesis, the Gases in the Overturning and Horizontal circulation of the Subpolar North Atlantic Program (GOHSNAP) team deployed oxygen sensors on oceanographic moorings across the Labrador Sea, beginning in 2020. Funding for this collaborative project led by researchers at the University of Rhode Island (URI), the Woods Hole Oceanographic Institution (WHOI), and Boston College (BC), provided 35 new oxygen sensors. Together with additional colleagues from WHOI and from Dalhousie University in Canada, we coordinated observational efforts to enable oxygen sensor coverage across the entire Labrador Sea and western Irminger Sea (Figure).

Deployment of the oxygen sensors for this project required the efforts of a large international team of collaborators. The moorings on which we deployed our oxygen sensors are maintained by teams from Germany, Canada, and the US, with four separate oceanographic research cruises handling the deployment and calibration of the moorings. Our team coordinated with scientists leading all of these cruises, and participated in the US-led field efforts. Despite challenges to seagoing fieldwork due to COVID-19 pandemic precautions during our initial sensor deployments, the combined efforts of the GOHSNAP team, our scientific collaborators, and the research vessels' captains and crews enabled us to successfully prepare and deploy all oxygen sensors. While our initial proposal for this project only included two years of data collection, from summer 2020 to summer 2022, we extended data collection by re-deploying the oxygen sensors on the moorings after they were recovered and the data was downloaded during research cruises in both 2022 and 2024.

The GOHSNAP team developed and implemented careful calibration procedures to ensure that the oxygen data we collected was as accurate as possible. These procedures included dedicated calibration activities during the oceanographic research cruises where the optodes were deployed on these moorings, as well as the follow-on cruises two years later when they were recovered. Our team published a synthesis of these procedures, providing recommendations to support the global ocean observing community's efforts to collect accurate oxygen data in other regions.

Applying these procedures to our data, we used oxygen sensor measurements from 2020-2022 to calculate oxygen uptake and transport out of the Labrador Sea. Our results support our initial hypothesis that the Labrador Sea plays a key role in oxygenation of the North Atlantic, due to decoupling between gas uptake and overturning transport by AMOC. These results will be presented in a scientific manuscript, currently in preparation. Additional ongoing analysis will consider the role of the Labrador Sea in carbon dioxide uptake, building on the oxygen analysis and measurements of dissolved carbon from seawater collected during the research cruises.

Last Modified: 05/29/2025
Modified by: Hilary Palevsky