Rapid transfer of oxygen to the deep ocean mediated by bubbles

Abstract

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. Bubble-mediated flux of oxygen into the Labrador Sea surface ocean contributes to air–sea gas exchange, suggest observations from moored profiling and Argo float data. Climate models that omit the process may underestimate oxygen in the deep ocean.