Preprints
https://doi.org/10.5194/egusphere-2024-1750
https://doi.org/10.5194/egusphere-2024-1750
20 Jun 2024
 | 20 Jun 2024
Status: this preprint is open for discussion.

Ocean carbon sink assessment via temperature and salinity data assimilation into a global ocean biogeochemistry model

Frauke Bunsen, Judith Hauck, Lars Nerger, and Sinhué Torres-Valdés

Abstract. Global ocean biogeochemistry models are frequently used to derive a comprehensive estimate of the global ocean carbon uptake. These models are designed to represent the most important processes of the ocean carbon cycle, but the idealized process representation and uncertainties in the initialization of model variables lead to errors in their predictions. Here, observations of ocean physics (temperature and salinity) are assimilated into the ocean biogeochemistry model FESOM-REcoM over the period 2010–2020 to study the effect on the air-sea CO2 flux and other biogeochemical variables. While the free running model already represents temperature and salinity rather well, the assimilation further improves it and hence influences the modeled ecosystem and CO2 fluxes. The assimilation has mainly regional effects on the air-sea CO2 flux, with the largest imprint of assimilation in the Southern Ocean during winter. South of 50° S, winter CO2 outgassing is reduced and thus the mean CO2 uptake increases by 0.18 Pg C yr-1 through the assimilation. Other particularly strong regional effects on the air-sea CO2 flux are located in the area of the North Atlantic Current. Yet, the effect on the global ocean carbon uptake is a comparatively small increase by 0.05 Pg C yr-1 induced by the assimilation, yielding a global mean uptake of 2.78 Pg C yr-1 for the period 2010–2020.

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Frauke Bunsen, Judith Hauck, Lars Nerger, and Sinhué Torres-Valdés

Status: open (until 23 Aug 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Frauke Bunsen, Judith Hauck, Lars Nerger, and Sinhué Torres-Valdés

Data sets

Processed model output underlying the manuscript figures Frauke Bunsen https://doi.org/10.5281/zenodo.11495081

Model code and software

Code to perform the free simulation and the data assimilation; plus, Jupyter Notebook to produce manuscript figures) Frauke Bunsen, PDAF group, FESOM-REcoM team https://doi.org/10.5281/zenodo.11495274

Frauke Bunsen, Judith Hauck, Lars Nerger, and Sinhué Torres-Valdés

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Short summary
Computer models are used to derive estimates of the ocean CO2 uptake. Because such idealized models don't always correspond precisely to the real-world, we combine real-world observations of ocean temperature and salinity with a model, and study the effect on the modeled air-sea CO2 flux (2010–2020). The corrections of temperature and salinity have their largest effect on regional CO2 fluxes in the Southern Ocean during winter, but a comparatively small effect on the global ocean CO2 uptake.