Sensitivity of the ocean oxygen inventory and the size of oxygen minimum zones to the particulate organic matter remineralization length scale

The e-folding length scale of sinking particulate carbon remineralization is known to modulate oceanic pCO₂ on steady state timescales, but the subsequent impact on the distribution of ocean pO₂ has not been similarly quantified. We use a global, data-constrained, steady state oxygen and phosphorus cycling model to show a large negative sensitivity between both the total ocean oxygen inventory and the size of oxygen minimum zones as the remineralization length scale is varied. Analogously to pCO₂, decreasing the length scale shifts the sources and sinks of O₂ and CO₂ to the younger and more rapidly ventilated upper water column; for example, we find that decreasing the length scale of remineralization from 275m to 165m increases the total oxygen content by over 30%. Unique to pO₂, however, we find that decreasing the length scale additionally concentrates oxygen demand in the waters already exhibiting the highest rates of oxygen utilization and lowest standing oxygen concentrations, which therefore acts to intensify and expand oxygen minimum zones, despite an increasing global inventory; for example, decreasing the length scale from 275m to 165m expands suboxic ([O₂] < 5 μM) habitat by over 500%. These results provide a unique steady state perspective on the global ocean oxygen cycle and quantify a strong biological control on the ocean oxygen distribution via bacterially mediated remineralization of sinking particles. More work needs to be done to understand the climatic sensitivity of the remineralization length scale in order to project how such changes may alter the oxygen cycle into the future and how they may interact with other changes in the ocean system.