The ocean has experienced intense deoxygenations over the last 250 million years, with evidence of global anoxia during the Mesozoic, called Oceanic Anoxic events (OAEs). OAEs are characterised by widespread depositions of organic-carbon-rich sediments and are associated with increased volcanic activity (causing high atmospheric CO₂, warming and eutrophication via enhanced weathering). Due to biogeochemical interactions, these past ocean deoxygenations impacted the nutrient cycles and marine ecosystem, strongly influencing the ocean nitrogen system. Estimating OAEs triggers and potential consequences can help us understand the impact of global warming on ocean oxygen levels and their coupling with other biogeochemical and ecological processes. Here, we apply an Earth System Model of intermediate complexity (cGEnIE) to 1) reconstruct the state of ocean deoxygenation during OAEs, 2) quantify the triggers of global anoxia (comparing temperature versus nutrient effect), and 3) assess the OAEs impact on the ocean nitrogen cycle and its ecology. We compare model sensitivity experiments with paleo-observations to accurately reconstruct the ocean state in oxygen and nutrient levels and contrast the OAEs with modern climate and other key paleo-ocean events. We conclude that OAEs were associated with dramatic changes in marine nutrients, oxygen and ecology, revealing stronger (while slower) perturbations than predicted in the future.

Primary Presenter: Fanny Monteiro, University of Bristol (f.monteiro@bristol.ac.uk)

Authors:

Rich Pancost,   ()

Patricia Sanchez-Baracaldo,   ()