Constraint on net primary productivity of the global ocean by Argo oxygen measurements

The biological transformation of dissolved inorganic carbon to organic carbon during photosynthesis in the ocean, marine primary production, is a fundamental driver of biogeochemical cycling, ocean health and Earth’s climate system. The organic matter created supports oceanic food webs, including fisheries, and is an essential control on atmospheric carbon dioxide levels. Marine primary productivity is sensitive to changes due to climate forcing, but observing the response at the global scale remains a major challenge. Sparsely distributed productivity measurements are made using samples collected and analysed on research vessels. However, there are never enough ships and scientists to enable direct observations at the global scale with seasonal to annual resolution. Today, global ocean productivity is estimated using remote-sensing ocean-colour observations or general circulation models with coupled biological models that are calibrated with the sparse shipboard measurements. Here we demonstrate the measurement of gross oxygen production by photosynthesis using the diel cycle of oxygen concentration detected with the array of Biogeochemical-Argo profiling floats. The global ocean net primary productivity computed from this data is 53 Pg C y−1, which will be an important constraint on satellite and general circulation model-based estimates of the ocean productivity. Argo measurements provide a constrained estimate of net primary productivity of the global ocean of 53 Pg C y–1, according to a global analysis of diel oxygen variations.