Impact of sub-mesoscale physics on production and subduction of phytoplankton in an oligotrophic regime

Abstract

Using a protocol of numerical experiments where horizontal resolution is progressively increased, we show that small-scale (or sub-mesoscale) physics has a strong impact on both mesoscale physics and phytoplankton production/subduction. Mesoscale and sub-mesoscale physics result from the nonlinear equilibration of an unstable baroclinic jet. The biogeochemicalcontext is oligotrophy. The explicitly resolved sub-mesoscales,at least smaller than one fth of the internal Rossby radius of deformation, reinforce the mesoscale eddy eld and contribute to double the primary production and phytoplankton subduction budgets. This enhancement is due to the reinforced mesoscale physics and is also achieved by the small-scale frontal dynamics. This sub-mesoscale physics is associated with density and vorticity gradients around and between the eddies. It triggers a signi cant small-scale nutrient injection in the surface layers, leading to a phytoplankton eld mostly dominated by ne spatial structures. It is believed that, depending on wind forcings, this scenario should work alternately with that of Abraham (1998) which invokes horizontal stirring of nutrient injected at large scales. Results also reveal a strong relationship between new production and negative vorticity, in the absence of wind forcing and during the period of formation of the eddies.

Influence of horizontal model grid resolution on the simulated primary production in an embedded primary production model in the Norwegian Sea

“…Lévy et al (2001) performed a process study in an oligothropic context, where the impacts of resolving mesoscale and submesoscale activity were examined. They found that the submesoscale (scale at ∼ 5-20 km) will increase the primary production even more compared to the mesoscale activity (scale at ∼ 20-50 km).…”

A global compilation of dissolved iron measurements: focus on distributions and processes in the Southern Ocean

“…Additionally, higher rates of upper ocean eddy kinetic energy (eddy genesis and meandering, EKE) in the South Atlantic are caused by current convergence/divergence predominantly at the Brazil-Malvinas Confluence (Maamaatuaiahutapu et al, 1998;Peterson and Stramma, 1990), the Agulhas Current retroflection and over the Atlantic mid-ocean ridge (Swart and Speich, 2010). Higher EKE provides a plausible mechanism whereby deeper waters with higher Fe concentrations can be supplied to the euphotic zone through upwelling processes (Archer and Johnson, 2000;Lévy et al, 2001;Klein and Lapeyre, 2009). On the other hand, the INDbasin's dust sources are at more northerly latitudes and only the Kerguelen Plateau and the Tasmanian shelf are potential margin sources (e.g., Boyd and Ellwood, 2010), which may mean that this basin receives less exogenous input of dFe.…”

Impact of episodic vertical fluxes on sea surface pCO 2

“…Potential mechanisms that can induce such events include negative buoyancy fluxes causing convection, frontal dynamics [12,13], localized upwelling/mixing owing to wind variability [14], storms and hurricanes [15], and proposed geoengineering schemes such as ocean pipes [16]. Indeed, the importance of such vertical mixing events on phytoplankton production and the biological pump is now widely recognized [17][18][19][20][21]. However, their effect on surface pCO 2 is more complex and difficult to generalize owing to the multiple factors that control pCO 2 .…”