Interactions between multiple physical particle injection pumps in the
Southern Ocean
Abstract
The biological pump, which removes carbon from the surface ocean and
regulates atmospheric carbon dioxide, comprises multiple processes that
include but extend beyond gravitational settling of organic particles.
Contributions to the biological pump that arise from the physical
circulation are broadly referred to as physical particle injection
pumps; a synthetic view of how these physical pumps interact with each
other and other components of the biological pump does not yet exist. In
this study, observations from a quasi-Lagrangian float and 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 and the eddy subduction pump. Estimated
independently, each mechanism contributes intermittent export fluxes on
the order of several hundreds milligrams of particulate organic carbon
(POC) per day. The float and the glider produce similar estimates of the
mixed layer pump, with sustained weekly periods of export fluxes with a
magnitude of 400 mg-POC-m-2-day-1. Export fluxes from the eddy
subduction pump, based on a mixed layer instability scaling,
occasionally exceed 500 mg-POC-m-2day-1, with some periods having strong
inferred vertical velocities and others having enhanced isopycnal
slopes. Regimes occur when a summation of the two pump estimates may
misrepresent the total physical carbon flux. Disentangling contributions
from different physical pump mechanisms from sparse data will remain
challenging. Insight into how mesoscale stirring and submesocale
velocities set the vertical structure of POC concentrations is
identified as a key target to reduce uncertainty in global carbon export
fluxes.