| Summary: | Dissolved oxygen (DO) concentration in the ocean is an important component of the marine biogeochemical cycles. In this study a global oceanic carbon cycle model (HAMOCC 2.0) was used to address how oxygen minimum zones (OMZ) respond to changes due to CO₂ radiative forcing. Atmospheric pCO₂ was increased at a rate of 1% annually and the model is stabilized at 2 X, 4 X, 6 X, and 8 X preindustrial pCO₂ levels. With an increase in CO₂ radiative forcing, the OMZ in the Pacific Ocean was controlled largely by changes in particulate organic carbon (POC) export. In contrast, the vertical expansion of the OMZs within the Atlantic and Indian Oceans were the result of changes to oxygen solubility. Changes in oxygen solubility also lead to the formation of a new OMZ in the western sub-tropical Pacific Ocean. The response of the pH value to a total carbon emission of 4480 PgC or 8 times preindustrial pCO₂ was found to be comparable to the ocean acidification at the PETM (56 Ma). The HAMOCC 2.0 simulations indicate a significant relationship between the pH value and the DO concentration at intermediate depth. This can lead to stress for the marine ecosystem by further decreasing pH due to respiratory processes. Improved parameterization may enhance the predictability of regions with low DO concentrations and pH value. A 50% increase in atmospheric dust deposition did not significantly alter the regions of Fe limitation of export production and hence did not resulted in significant changes in DO in the twilight zone and at intermediate depth. However, a 50% reduction in dust deposition significantly expanded the regions of Fe-limited export production thereby reducing the vertical particle flux of POC and the extent of the OMZs. This counteracted the OMZ expansion due to the increased CO₂ radiative forcing. Winguth, Arne M. E.
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