Award: OCE-1756613

The ocean plays a central role in the global carbon cycle, taking up carbon from the atmosphere via physical, chemical, and biological processes. The subpolar North Atlantic in particular is a hotspot for carbon uptake due to the deep winter mixing and strong spring and summer phytoplankton blooms (Fig 1). These processes are highly seasonal and require continuous measurements throughout the year to monitor; however, most prior studies have focused just on the spring and summer season, when the weather is more conducive for fieldwork on ships. The Ocean Observatories Initiative (OOI) Irminger Sea Global Array of moorings and gliders (Fig 2) provides a unique opportunity to investigate these processes due to an unprecedented density of biogeochemical, physical, and bio-optical sensors operating year-round for multiple years at high temporal resolution. In this project, we developed new methodologies to improve the accuracy of OOI Irminger Sea Array oxygen measurements by deploying autonomous underwater vehicles (gliders) configured to calibrate their oxygen optodes in air when surfacing between profiles (Fig 3). The success of our project-supported deployments of gliders with air-calibrating oxygen sensors led to the wider adoption of the method by the entire OOI program. After successfully participating in research cruises to the OOI Irminger Sea Array in 2018 and 2019, the fieldwork limitations caused by the COVID-19 pandemic led our team to continue collaborating with the OOI program to support collection of high-quality oxygen data during the OOI Irminger Sea cruise in 2020, as well as in subsequent years. Building on this expanded temporal scope, we are currently completing work on a calibrated oxygen dataset for the entire period from 2014-2022 for the site, including all measurements made during seagoing cruises as well as measurements made from sensors deployed throughout the year. Our team also expanded the scope of our research beyond the original focus on oxygen measurements on OOI gliders to a more comprehensive assessment of the quality of biogeochemical sensor measurements across the OOI Irminger Array as well as on observing assets in the region such as Biogeochemical Argo floats. One key result of this expanded scope was the initiation of an OOI Biogeochemical Sensor Data Working Group, which convened 39 experts from around the world for both virtual and in person workshops, and produced a user guide and recommendations to help other scientists prepare these sensor data for scientific analysis. Results from the project have been presented at numerous national and international conferences. Some have been published, with several manuscripts still in preparation. Our findings so far highlight strong variations from year to year in strength of winter mixing, driven primarily by variations in winter air temperatures and storminess, as well as variations in the strength of the spring and summer phytoplankton bloom and the amount of carbon that sinks out of the surface and is stored at depth. Our ongoing work analyzing these results will continue to investigate the linkages between the physical and biological processes in driving carbon cycling in the region. The project has provided research opportunities for a Postdoctoral Researcher, three Ph.D. students, a M.S. student, and five undergraduate research students. This project provided four of these undergraduate students with their first ever opportunity to participate in seagoing fieldwork, and supported one of these students in subsequently completing an undergraduate senior thesis and continuing on for PhD studies in oceanography. This project also supported the development of educational activities incorporating authentic OOI data for use in both introductory and advanced undergraduate classes. These activities have been used to date with ~150 students enrolled in 6 different classes, and have also been disseminated to the broader marine and geoscience education communities through a publication, blog post, and conference talk. Last Modified: 06/29/2023 Submitted by: David Nicholson