Transient modeling for the ocean redox condition during the mid-Cretaceous oceanic anoxic event 2

Oceanic Anoxic Event 2 (OAE2) is one of the largest disruptions for the global carbon cycle in the mid-Cretaceous, which was linked to global warming and nutrient release from continental weathering. However, their respective contributions to the seafloor anoxia remain unclear. Here we perform transient numerical simulations using an intermediate-complexity Earth system model to study their influences on the mid-Cretaceous OAE2. The modeling results show that global warming due to carbon dioxide degassing could influence the seafloor oxygen contents distinctly through the ocean circulation change, but has a minor influence on the seafloor anoxia during the OAE2. The phosphate due to continental weathering associated with global warming added to the ocean further decreases the seafloor oxygen content, especially leading to the North Atlantic seafloor anoxic area expansion and the anoxia of the Southeastern Pacific Basin. When different continental weathering rates are taken into account, the modeled anoxic area from simulations with an increase of approximately 1.3 to 1.7 times the pre-OAE2 level is comparable with the estimate based on proxies, which tentatively constrains the continental weathering rate during the OAE2. This simulation would enhance our understanding of the intricate biological and geochemical processes in the oceans as the increasing atmospheric carbon dioxide concentrations.