Publication Date:
2018-03-16
Description:
According to a recent study, C:N ratios of sinking particulate organic matter (POM) in the ocean appear to be higher than Redfield (7.1 instead of 6.6) and depth dependent (increase +0.2/km). Here we investigate the effects of vertically variable C:N element ratios on marine carbon fluxes and the air-sea exchange of CO2 using a global ocean carbon cycle model (AAMOCC). For a steady-state ocean, the results show that models using the constant classical Redfield ratio underestimate both, total inventory and vertical gradients of dissolved inorganic carbon (DIC). While the amount of additional DIC (+150 Gt C) is negligible compared to the high marine carbon inventory, the C:N depth dependence can reduce the ambient atmospheric pCO2 by 20 ppm, permanently. Moreover, the simulation of a future scenario, estimating a possible effect of CO2-dependent C:N ratios of POM on the marine carbon cycle, has shown that even a moderate rise in the C:N element ratio of sinking POM, which is on the order of magnitude of natural variability, yields a considerably higher oceanic uptake of anthropogenic CO2 on timescales of decades to centuries. The assumption is based on a predicted increase in the production of highly carbon enriched transparent exopolymer particles (TEP) caused by rising atmospheric CO2 concentrations and enhanced nutrient limitation. However, counteracting a predicted decrease of the physical (solubility) CO2 pump as a consequence of global change, the effect in our scenario will alleviate further rising atmospheric CO2 concentrations rather than compensate a reduced physical uptake.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1029/2003GB002184
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