Abstract
Abstract. Since the seminal paper of Redfield (1934), constant stoichiometric elemental ratios linking biotic carbon and nutrient fluxes are often assumed in marine biogeochemistry, and especially in coupled biogeochemical circulation models, to couple the global oxygen, carbon and nutrient cycles. However, when looking in more detail, some deviations from the classical Redfield stoichiometry have been reported, in particular with respect to remineralization of organic matter changing with depth or with ambient oxygen levels. We here compare the assumptions about the stoichiometry of organic matter and its remineralization that are used explicitly and implicitly in common biogeochemical ocean models. We find that the implicit assumptions made about the hydrogen content of organic matter can lead to inconsistencies in the modeled remineralization and denitrification stoichiometries. It is suggested that future marine biogeochemical models explicitly state the chemical composition assumed for the organic matter, including its oxygen and hydrogen content.
Highlights
The relative success of coupled biogeochemical (BGC) circulation models in simulating the oceanic component of the global carbon cycle relies to a large extent on the assumption of constant stoichiometric ratios linking biotic carbon and nutrient fluxes (Redfield, 1934)
We find that the implicit assumptions made about the hydrogen content of organic matter can lead to inconsistencies in the modeled remineralization and denitrification stoichiometries
Using the above considerations about the relation between organic matter stoichiometry and the stoichiometries of the different aerobic and anaerobic processes, we aim to examine the parameterisation in four different global biogeochemical models: HAMOCC, PISCES, BEC and SCHMITTNER
Summary
The relative success of coupled biogeochemical (BGC) circulation models in simulating the oceanic component of the global carbon cycle relies to a large extent on the assumption of constant stoichiometric ratios linking biotic carbon and nutrient fluxes (Redfield, 1934). – the SCHMITTNER model, Schmittner et al, 2008) All these global biogeochemical models are extensions of NPZD (nutrient, phytoplankton, zooplankton, detritus) type ecosystem models including aerobic remineralisation, denitrification and nitrogen fixation. SCHMITTNER uses an expanded NPZD ecosystem model with a parameterization of fast nutrient recycling due to microbial activity that emerged from a North Atlantic data assimilation study (Schartau and Oschlies, 2003) Referring to these models we will in this note examine the specific assumptions about the C/P, N/P, -O2/P and -NO3/P ratios used in the respective models, and how these differ among the different models. The explicit and implicit assumptions made by the different biogeochemical models are discussed in Sect. 4, before Sect. 5 concludes the short note with a discussion of the possible impacts of using different stoichiometric assumptions in different biogeochemical models
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