Annual Oxygen Budget for the Subpolar North Atlantic using Air-calibrated Glider and Mooring Data from the Ocean Observatories Initiative Irminger Sea Array

The subpolar North Atlantic features strong springtime biological production that exports organic carbon from the stratified seasonal mixed layer as well as wintertime deep mixing that ventilates respired carbon back to the atmosphere. Determining the net amount of organic carbon that escapes winter ventilation and is ultimately sequestered from the atmosphere requires biogeochemical tracer measurements throughout the full annual cycle. Dissolved oxygen sensors on moorings and gliders continuously deployed at the Ocean Observatories Initiative (OOI) Irminger Sea array (60°N, 40°W) since September 2014 provide a novel opportunity to observe these processes, but limitations of sensor calibration and stability have heretofore precluded quantitative estimates of air-sea gas exchange and net community production, which require highly accurate mixed layer oxygen measurements.

To address this challenge, two gliders equipped with oxygen optodes positioned to enable surface air measurements were deployed at the OOI Irminger Sea array in June 2018, providing improved sensor calibration over the subsequent year. These gliders patrolled the array, profiling to 1000 m and intercalibrating with eight moored oxygen optodes, one on a subsurface profiler (200-2600 m) and the others at fixed depths (1-130 m). The combined glider and mooring data provide the first year-round full-depth oxygen data determined with sufficient accuracy to enable quantitative interpretation of the relative contributions of air-sea gas exchange, net community production, and subsurface respiration in this region. We will present the 2018-2019 oxygen budget in the context of the full OOI time-series, which shows that 2018-2019 winter ventilation was the shallowest since 2014 (250-300 m, compared to 800-1400 m in previous years), reducing the extent of physical ventilation of respired carbon and demonstrating the need for continued time-series measurements to quantify interannual variability in this region.