The concentration of oxygen exerts major controls on life in the ocean, and its distribution in the ocean and atmosphere carries information about biological productivity, transports of mass and heat, ocean deoxygenation and global carbon sinks. Our understanding of processes underlying oxygen distributions, their key features and variability is often lacking. Here we investigate the magnitude, variability and uncertainty of the air–sea flux of oxygen, carbon dioxide and atmospheric potential oxygen over an annual cycle in the Labrador Sea. We demonstrate that two-thirds of the annual oxygen uptake occurs over only 40 days in winter and is associated with a bubble-mediated component of air–sea gas transfer linked to episodic high winds, strong cooling and deep convective mixing. By neglecting the bubble-mediated flux component, global models may underestimate oxygen and atmospheric potential oxygen uptake in regions of convective deep-water formation by up to an order of magnitude. Uncertainties in wind speed products lead to additional major (up to 80%) uncertainty in air–sea fluxes in these critical regions. Our findings may help explain observation–model discrepancies in distributions of atmospheric potential oxygen and imply that oxygen levels in the deep ocean are more sensitive to climate change than currently thought.
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The SeaCycler and Argo data used for air–sea flux calculations are available at https://doi.org/10.6084/m9.figshare.10765907. Argo data are also available through the USGODAE Argo GDAC (ftp://usgodae.org/pub/outgoing/argo/). NCEP Daily Global Analyses (NCEP) and NCEP North American Regional Reanalysis (NARR) data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Website at https://www.esrl.noaa.gov/psd/. CCMP Version 2.0 vector wind analyses are produced by Remote Sensing Systems. Data are available at www.remss.com. C-2015 ASCAT data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Vector Winds Science Team. Data are available at www.remss.com. ERAI data can be obtained from the ECMWF data portal (https://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/). MERRA-2 data can be obtained from Goddard Earth Sciences Data and Information Services Center (GES DISC) at https://goldsmr4.gesdisc.eosdis.nasa.gov/data/MERRA2/M2T1NXFLX.5.12.4/. CGRF data were obtained from Paul Myers and Xianmin Hu (University of Alberta) and can be provided on request to the authors.
The MATLAB code for calculation of fluxes is available, on request, from the corresponding author. The code is an adaptation of known equations described in Methods (Flux methodology).
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This work was funded in part by the Canada Excellence Research Chair in Ocean Science and Technology, NSERC through the CCAR VITALS network under 433898-2012 to P. Myers and the Ocean Frontier Institute (OFI). The SeaCycler platform was developed with funding from the US NSF OCE Technology grant OCE0501783. We thank J. Karstensen (GEOMAR), O. Zielinski (University of Oldenburg), the captain and crew of R/V Maria S Merian for support in deployment and recovery of the SeaCycler mooring. The authors acknowledge contribution from the Bedford Institute of Oceanography (Department of Fisheries and Oceans Canada), G. Siddall and their engineering team. J.K. was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program—Grant NNX16AO39H.
The authors declare no competing interests.
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Atamanchuk, D., Koelling, J., Send, U. et al. Rapid transfer of oxygen to the deep ocean mediated by bubbles. Nat. Geosci. 13, 232–237 (2020). https://doi.org/10.1038/s41561-020-0532-2