Ocean Deoxygenation Conference | Kiel 2018

All Earth System models project a consistent decrease in the oxygen content of the ocean for the coming decades. The processes at play in each of the models are ocean warming, reduced ventilation and increased stratification. At the regional scale and for the subsurface ocean however, these model projections are much less robust, which reflect a complex interplay of processes responsible for the the changes in ocean oxygen levels. In this presentation, I make use of simulations performed in the context of the Coupled Model Intercomparison project 5 (CMIP5). I will show that the sub-surface deoxygenation trend is partly balanced by a reduction in sub-surface respiration. I will also show that in many of these models, the tropical ocean undergoes partial re-ventilation, and hence a rejuvenation of the sub-surface water masses, even in case of increased vertical stratification. This may lead to a partial tropical sub-surface re-oxygenation with global warming. To get more insights into the role of ventilation in oxygen trends, changes in oxygen fluxes are analysed at the based of the mixed layer in one of the CMIP5 models. I also turn to past climates, such as the Last Glacial Maximum, or even deep time anoxic events, to decipher the role of ventilation in driving past changes in oxygen.