Final Report Summary - BIGCOW (Biogeochemistry in a high CO2 world: Lessons from the ocean anoxic events)
Ancient oceanic anoxic events (OAEs) represent profound perturbations of the global carbon cycle and oxygenation of the global oceans and are the times when much of the world's oil and gas reserves were formed during deposition of unusually organic carbon rich 'black shale' layers in marine sediments. This project assessed the relative importance of changes in oxygen supply (combining oxygen solubility and ocean circulation) and marine productivity in creating these extreme environmental conditions. An Earth system model was set up to account for the main ocean dynamics and biogeochemistry of the cretaceous climate. The impact of higher temperatures and marine productivity were then evaluated in the model against a new compilation of observations for seafloor anoxia. The model shows that temperature is not able alone to reproduce observations but rather the observed patterns of ocean anoxia are reproduced mainly via enhanced marine productivity due to higher nutrient content. The results have implications for our understanding of how the Earth system responds to long-term carbon dioxide (CO2) release and warming and how and when conditions for oil source rock formation are created. The finding that warming alone exerts only a minor influence in promoting seafloor anoxia reduces the concerns that any such similar occurrence could be a possibility in the near future.