Physical and biogeochemical responses to the GEOMETRIC eddy parameterisation in an idealised ocean model
Julian Mak (Hong Kong University of Science and Technology)
Séminaire du LOCEAN
The stratification of the ocean affects transport pathways, in turn affecting biogeochemical responses via changes to the deep nutrient supply for example. With that in mind, although there has been substantial activity in the development of mesoscale eddy parameterisations for use in numerical ocean models, most of the related works have focused on the associated impacts on the physical state, bypassing the biogeochemical response. Here, we employ a recently developed energetically constrained eddy parameterisation GEOMETRIC that has been demonstrated to improve the physical response, and assess its associated impact on the biogeochemistry response within an idealised gyre model.
At coarse resolutions, there is evidence suggesting GEOMETRIC leads to an improved response and sensitivity in the stratification and overturning. While there are some improvements to the nutrient supply
and net primary production in the pre-industrial scenario, the sensitivity under climate change scenarios is more subtle. At eddy permitting resolutions, a choice has to be made on whether to employ an eddy parameterisation. If yes, the parameterisation essentially swamps the explicit eddies permitted by the model, and the results bear similarities to the coarse resolution models. If no, the explicit eddies are too weak, the overturning is too strong because the stratification is too deep, and the resulting net primary productionis too large. We propose a new methodology that takes a middle ground between the « fully parameterise » and « no parameterisation » regime, and demonstrate improvements in the model response in both the pre-industrial and climate change scenario.
Sorbonne Université, Campus Pierre et Marie Curie (Jussieu)
Couloir 45-55, 4e étage, pièce 417