Response of export production and dissolved oxygen concentrations in oxygen minimum zones to pCO₂ and temperature stabilization scenarios in the biogeochemical model HAMOCC 2.0

Abstract. Dissolved oxygen (DO) concentration in the ocean is an important component of marine biogeochemical cycles and will be greatly altered as climate change persists. In this study a global oceanic carbon cycle model (HAMOCC 2.0) is used to address how mechanisms of oxygen minimum zone (OMZ) expansion respond to changes in CO₂ radiative forcing. Atmospheric pCO₂ is increased at a rate of 1 % annually and the model is stabilized at 2 ×, 4 ×, 6  ×, and 8 × preindustrial pCO₂ levels. With an increase in CO₂ radiative forcing, the OMZ in the Pacific Ocean is controlled largely by changes in particulate organic carbon (POC) export, resulting in increased remineralization and thus expanding the OMZs within the tropical Pacific Ocean. A potential decline in primary producers in the future as a result of environmental stress due to ocean warming and acidification could lead to a substantial reduction in POC export production, vertical POC flux, and thus increased DO concentration particularly in the Pacific Ocean at a depth of 600–800 m. In contrast, the vertical expansion of the OMZs within the Atlantic is linked to increases POC flux as well as changes in oxygen solubility with increasing seawater temperature. Changes in total organic carbon and increase sea surface temperature (SST) also lead to the formation of a new OMZ in the western subtropical Pacific Ocean. The development of the new OMZ results in dissolved oxygen concentration of  ≤  50 µmol kg⁻¹ throughout the equatorial Pacific Ocean at 4 times preindustrial pCO₂. Total ocean volume with dissolved oxygen concentrations of  ≤  50 µmol kg⁻¹ increases by 2.4, 5.0, and 10.5 % for the 2 ×, 4 ×, and 8 × CO₂ simulations, respectively.