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.
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The profiling float data used in this study were obtained in December 2020 by downloading all Argo Sprof files directly from the Argo Global Data Assembly Center (ftp://usgodae.org/pub/outgoing/argo or ftp://ftp.ifremer.fr/ifremer/argo). The corresponding monthly snapshot (December 2020) of the Argo database, which contains these Sprof files in addition to all floats that do not have biogeochemical sensors, is https://doi.org/10.17882/42182#79118. The Sprof files for floats with adjusted oxygen concentrations were then merged into netCDF files for the Northern and Southern Hemispheres and used for the analyses reported here. These files are available at https://doi.org/10.5281/zenodo.4989023. Monthly satellite data were downloaded from http://www.science.oregonstate.edu/ocean.productivity/.
Analyses were performed in Matlab. Code used in this analysis is available at https://doi.org/10.5281/zenodo.4989023.
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This work was supported by the Global Ocean Biogeochemical Array project (NSF OCE-1946578; publication no. 1), the Southern Ocean Carbon and Climate Observations and Modeling project (NSF PLR-1425989 and OPP-1936222) and the David and Lucile Packard Foundation. Profiling floats in the equatorial Pacific were supported by NOAA under grant NA16OAR4310161 to the University of Washington. We thank J. Long for assistance with the satellite data, and T. Maurer and J. Plant for processing data and assistance with coding. S. Riser and D. Swift prepared many of the profiling floats whose data were used in this analysis. We thank the Hawaii Ocean Time-series and Bermuda Atlantic Time-series Station programmes for making their data easily accessible. The float data were collected and made freely available by the International Argo Program and the national programmes that contribute to it (https://argo.ucsd.edu, https://www.ocean-ops.org). The Argo Program is part of the Global Ocean Observing System.
The authors declare no competing interests.
Peer review information Nature Geoscience thanks Benedetto Barone and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Xujia Jiang.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Figure 1. Profiling float oxygen data at surface versus time. a, Dissolved oxygen and b, Oxygen Anomaly = Oxygen – Oxygen Saturation in the upper 10 m for all adjusted oxygen data with quality flag = 1 (good data) in the Argo Global Data Assembly Center, except for 9 floats listed in Extended Data Table 1.
Global (60°N to 60°S) oxygen and GOP values for the years 2016 through 2020. a, Mean oxygen anomaly in the upper 20 m from each profile with acceptable cycle timing versus local hour of the day. b, Mean oxygen anomaly in each hourly interval and the least squares fit of equation 2 to the data shown in a) with GOP = 2.1 ± 0.4 (1 Std Error) mmol O2 m−3 d−1.
Extended Data Fig. 3 Annual mean NPP rates from 2010 through 2020 in each 10° latitude band from 50°N to 50°S.
Annual mean NPP rates from 2010 through 2020 in each 10° latitude band from 50°N to 50°S. a, Float and satellite NPP rates versus latitude. b, Satellite NPP rates in each 10° latitude band for each model versus float NPP rates. Satellite NPP models include VGPM21, CBPM24, and CAFE40. All values from Table 1.
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Johnson, K.S., Bif, M.B. Constraint on net primary productivity of the global ocean by Argo oxygen measurements. Nat. Geosci. 14, 769–774 (2021). https://doi.org/10.1038/s41561-021-00807-z