Effect of submesoscale dynamics and baroclinic instabilities on phytoplankton

Marine phytoplankton play a vital role in global biogeochemical cycles, accounting for roughly half of global primary production (Beardall 2009). Climate change is expected to alter physical conditions in the ocean leading to a loss of functional diversity in phytoplankton (Dutkiewicz 2021). However, due to the complexity and scale of phytoplankton communities and the physical processes that shape them, the details of these changes are poorly understood. Ocean mixing, which governs nutrient and organism transport essential to phytoplankton communities, is thought to be of particular importance to plankton community evolution and divergence (Coles 2017). In this work, we aim to examine the effect of submesoscale processes on phytoplankton community productivity and divergence with computer simulation experiments. As a first step, we will represent physical mechanisms for submesoscale eddy formation by using MIT-GCM, because primary mechanisms for submesoscale eddy formation are thought to be baroclinic instability and drag vorticity generation due to ocean topography (McWilliams 2019).

Previous simulation experiments showed that increasing spatial resolution from mesoscale-resolving (~10 km) to submesoscale resolving scales (~2 km), allowed for the emergence of a denser vortex populations, resulting in an increased phytoplankton abundance (Levy et al 2012). In this study, the validity of this barotropic model assumption is examined at varying spatial horizontal resolution (~50 km, 10 km, 2 km). MIT-GCM simulations are performed in a baroclinic rectangular basin (3180 km x 2180 km) with a depth of 4000 m, representing an idealized portion of the North Atlantic Ocean. Furthermore, simulation results for a basin with idealized flat-bottom topography and more realistic topography are compared. The validity of barotropic model assumptions, significance of topography and potential effects on marine phytoplankton are discussed. In the near future, we have plans to extend this model simulation approach to a range of topographies, such as coastlines and continental shelfs, in order to discuss interaction mechanisms between oceanic physical processes and plankton distribution in those regions.

References
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Coles, V. J., et al. "Ocean biogeochemistry modeled with emergent trait-based genomics." Science 358.6367 (2017): 1149-1154. 
Dutkiewicz, Stephanie, Philip W. Boyd, and Ulf Riebesell. "Exploring biogeochemical and ecological redundancy in phytoplankton communities in the global ocean." Global change biology 27.6 (2021): 1196-1213.
Lévy, Marina, et al. "Large-scale impacts of submesoscale dynamics on phytoplankton: Local and remote effects." Ocean Modelling 43 (2012): 77-93.
McWilliams, James C. "A survey of submesoscale currents." Geoscience Letters 6.1 (2019): 1-15.