Relevant passage:
Applying our model to today’s atmosphere-ocean state with an enhanced anthropogenic P flux from land in a sustained 130% excess over average Phanerozoic continental P weathering rates will ultimately trigger the anoxia-P-dependent cascade again in a manner that locks the oceans into an extensively anoxic state for more than half a million years. The oceanic redox state passes a tipping point when the oceanic P/O2 ratio is ∼2.3 and continues into a eutrophic ocean state with 3.5 times higher P/O2 than today and sustained high productivity and organic C burial. The Earth system tips back into the oxic ocean state as atmospheric O2 levels rise and cause oceanic P/O2 ratio to decline below the tipping point (Figure 4). The dynamics of the event depend critically on the formulation of the anoxia function, which is assumed represented by a sigmoidal function with parameters calibrated in 3D (GENIE)64 and 1D (CANOPS)65 Earth System models. The new sedimentation-dependent formulation of the benthic P flux does make the oceans more sensitive towards runaway anoxia when anoxia develops in shallower depths, but our model still requires a long period (>104 years) of sustained P input to pass the tipping point for global marine anoxia today. With oceanic P input at a sustained 130% excess over average Phanerozoic continental P weathering rates for ∼120 ka, anthropogenic forcing will eventually trigger the anoxia-P-dependent cascade in a manner that locks the oceans into an extensively anoxic ocean state for more than 0.5 Ma until oceanic P/O2 begins to decline as a result of rising atmospheric O2 levels (Figure 4).