Simulated 21st century's increase in oceanic suboxia by CO2-enhanced biotic carbon export

• Published in: Global Biogeochemical Cycles
• Main Authors: Oschlies, Andreas, Schulz, K. G., Riebesell, Ulf, Schmittner, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 2008
• Subjects: Ocean acidification
• Online Access: https://oceanrep.geomar.de/id/eprint/7398/; https://oceanrep.geomar.de/id/eprint/7398/1/364_Oschlies_2008_Simulated21stCenturysIncreaseIn_Artzeit_pubid10583.pdf; https://doi.org/10.1029/2007GB003147

The primary impacts of anthropogenic CO2 emissions on marine biogeochemical cycles predicted so far include ocean acidification, global warming induced shifts in biogeographical provinces, and a possible negative feedback on atmospheric CO2 levels by CO2‐fertilized biological production. Here we report a new potentially significant impact on the oxygen‐minimum zones of the tropical oceans. Using a model of global climate, ocean circulation, and biogeochemical cycling, we extrapolate mesocosm‐derived experimental findings of a pCO2‐sensitive increase in biotic carbon‐to‐nitrogen drawdown to the global ocean. For a simulation run from the onset of the industrial revolution until A.D. 2100 under a “business‐as‐usual” scenario for anthropogenic CO2 emissions, our model predicts a negative feedback on atmospheric CO2 levels, which amounts to 34 Gt C by the end of this century. While this represents a small alteration of the anthropogenic perturbation of the carbon cycle, the model results reveal a dramatic 50% increase in the suboxic water volume by the end of this century in response to the respiration of excess organic carbon formed at higher CO2 levels. This is a significant expansion of the marine “dead zones” with severe implications not only for all higher life forms but also for oxygen‐sensitive nutrient recycling and, hence, for oceanic nutrient inventories.