290 / 2024-09-13 15:22:04

Transient Modeling for Ocean Redox Conditions during the Mid-Cretaceous Oceanic Anoxic Event 2

OAE 2,paleoclimate modeling,ocean anoxia

Oceanic Anoxic Event 2 (OAE2) is one of the largest disruptions for the global carbon cycle in the mid-Cretaceous. Reconstructions of the OAE2 indicate that the ocean redox state was temporally and spatially heterogeneous. Its evolution is considered to be induced by the variation of atmospheric carbon dioxide concentrations (pCO₂) due to the activities of large igneous provinces (LIPs) and associated changes in global meridional overturning circulation, nutrient input, and phosphorus recycling. However, the changes/dynamics of anoxia, marine and atmospheric circulation, and weathering intensity during OAE2 are still under debate. Here we conduct transient numerical simulations using an intermediate-complexity Earth system model. Simulations show that an increase nutrient concentration due to increased continental weathering along with elevated pCO₂ levels can evidently lead to a marked increase in anoxic areas, which are further expanded by phosphorus recycling in the low-oxygen marine area. The modeled anoxic areas exhibit spatio-temporally distinctly different patterns during OAE2 with varying intensities of weathering. By comparing these with newly assembled geological records, it is speculated that anoxic bottom water conditions only accounted for ~30% of the global seafloor area, and that the continental weathering intensity was increased by ~40-60% compared to that of pre-OAE2 levels.