Public thesis defense of Justin Gérard: "Mechanisms of Devonian ocean anoxic events: insights from Earth system modelling"

Summary

Recurrent events of severe ocean deoxygenation during the Devonian Period represent major disruptions of the marine environment, yet many mysteries still surround them. 

To address specific aspects of these events, we use the Earth system model of intermediate complexity cGENIE to investigate the controls on ocean oxygenation through a series of targeted numerical experiments. 

Our results highlight the dominant role of continental configuration in shaping ocean circulation and modulating the response of oxygenation to other environmental and climatic forcings. 

We further show that astronomical forcing can strongly influence ocean oxygen through its control on continental nutrient weathering fluxes and biological productivity, producing substantial spatially contrasted responses, and intervals of eccentricity maxima associated with increased anoxia. 

Finally, model–data comparisons for the Kellwasser events indicate that increased nutrient availability can adequately reproduce the extent and seafloor fraction of anoxia, providing quantitative benchmarks against which different mechanisms and hypotheses can be tested.

Jury members

Prof. Michel Crucifix (UCLouvain) (Supervisor)
Prof. Anne-Christine Da Silva (ULiège) (Supervisor)
Prof. Qiuzhen Yin (UCLouvain) (President)
Prof. Hugues Goosse (UCLouvain) (Secretary)
Dr. Alexandre Pohl (Biogéosciences Dijon)
Prof. Georg Feulner (Potsdam Institute for Climate Impact Research)
Dr. Pam Vervoort (University of Birmingham)