Global ocean product of profiles of nutrients and carbonate system variables within the framework of Copernicus Multi Observations Thematic Assembly Center (MOBTAC)

To better understand the global ocean biogeochemical processes, it is crucial to strengthen the spatial coverage of high-quality biogeochemical variables. In this context, we provide high-quality nutrients (nitrate, phosphate and silicate) and carbonate system variables (total alkalinity, dissolved inorganic carbon, pH and partial pressure of carbon dioxide) profiles for BGC-Argo floats equipped with oxygen sensors and data qualified in delayed mode. These variables are derived using neural network models called CANYON-B and CONTENT for nutrients and carbonate system variables, respectively. For the Mediterranean Sea, we deliver these variables from a regional dedicated model called CANYON-MED. These variables are distributed from September 2002 to August 2022 as part of CMEMS MOBTAC service. The last update of the product will be available in CMEMS portal from March 2023.

At the global scale, nitrate, phosphate and silicate are retrieved with an accuracy (from the root mean squared difference) of 0.68, 0.051, 2.3 µmol kg^-1_, respectivelyand the carbonate system variables, i.e., total alkalinity, dissolved inorganic carbon, pH and partial pressure of carbon dioxide are retrieved with an accuracy of 6.2 µmol kg^-1, 6.9 µmol kg^-1, 0.013 (unitless), and 15 µatm, respectively. The global models (CANYON-B and CONTENT) have also been validated with independent data collected from recent various oceanic cruises not used for the development of the methods (from GLODAPv2.2021 database) and the Hawaii Ocean Time series (HOT). These independent validations demonstrate the validity of these models for global ocean applications. The nitrate and pH products were again validated against measured nitrate and pH from BGC-Argo floats equipped with oxygen sensors. Overall validation results were quite satisfactory at global and regional spatial scales.

Currently, the profiles are available for BGC-Argo floats with concurrent profiles of temperature, salinity and oxygen qualified in delayed mode. This product will be also available from near real-time observations from 2024.