Interactions Between Multiple Physical Particle Injection Pumps in the Southern Ocean

Abstract

Contributions to the biological pump that arise from the physical circulation are referred to as physical particle injection pumps. A synthesized view of how these physical pumps interact with each other and other components of the biological pump does not yet exist. Here, observations from a quasi-Lagrangian float and an ocean glider, deployed in the Southern Ocean's Subantarctic Zone for one month during the spring bloom, offer insight into daily-to-monthly fluctuations in the mixed layer pump (MLP) and the eddy subduction pump (ESP). Estimated independently, each mechanism contributes intermittent export fluxes of roughly several hundred milligrams of particulate organic carbon (POC) per square meter per day. The glider-based estimates indicate sustained weekly periods of MLP export fluxes across the base of the mixed layer with a magnitude of $\sim 450\pm 110$ mg POC $m^{-2}$ ${\text{day}}^{-1}$. Potential export fluxes from the ESP, based on a mixed layer instability scaling, occasionally exceed 400 mg POC $m^{-2}$ ${\text{day}}^{-1}$, with export elevated due to both strong inferred vertical velocities and enhanced isopycnal slopes. Significant export fluxes from the ESP are localized to the edges of mesoscale eddies and to fronts, whereas the MLP acts more broadly due to the larger scales of atmospheric forcing. Regimes occur when MLP and ESP export fluxes can have either the same or opposite sign. Simple summation of fluxes from existing parameterizations of the two pumps likely misrepresents the total physical carbon flux. Insights into how mesoscale stirring and submesoscale velocities set POC vertical structure is a key target to reduce uncertainty in global carbon export fluxes.