Oschlies A, Schulz KG, Riebesell U, Schmittner A
co2, emmissions, hypoxia, dead zones, mesocosm, metadata, model, Espegrend, Bergen, 11 m3, Norway
The primary impacts of anthropogenic CO2 emissions on marine biogeochemicalcycles predicted so far include ocean acidification, global warming induced shifts inbiogeographical provinces, and a possible negative feedback on atmospheric CO2 levelsby CO2-fertilized biological production. Here we report a new potentially significantimpact on the oxygen-minimum zones of the tropical oceans. Using a model of globalclimate, ocean circulation, and biogeochemical cycling, we extrapolate mesocosmderivedexperimental findings of a pCO2-sensitive increase in biotic carbon-to-nitrogendrawdown to the global ocean. For a simulation run from the onset of the industrialrevolution until A.D. 2100 under a ‘‘business-as-usual’’ scenario for anthropogenic CO2emissions, our model predicts a negative feedback on atmospheric CO2 levels, whichamounts to 34 Gt C by the end of this century. While this represents a small alteration ofthe anthropogenic perturbation of the carbon cycle, the model results reveal a dramatic50% increase in the suboxic water volume by the end of this century in response tothe respiration of excess organic carbon formed at higher CO2 levels. This is a significantexpansion of the marine ‘‘dead zones’’ with severe implications not only for all higherlife forms but also for oxygen-sensitive nutrient recycling and, hence, for oceanicnutrient inventories.