Is the vertical flux of nutrients influenced by phytoplankton physiology?

Frontal intensification, submesoscale dynamics, and ageostrophic circulations can intensify the vertical velocities in the ocean. But the vertical flux of tracer, such as nutrients for phytoplankton production, depends not only on the vertical velocity, but also on the gradient in the nutrient profile, which is affected by the phytoplankton’s uptake rate or growth rate. We explore how the vertical flux of a nutrient responds to the biological growth rate, a physiological characteristic of the phytoplankton. An optimum rate of nutrient supply and biomass growth are attained when the uptake rate matches the physical supply rate. In a three-dimensional model setting, the co-variances between vertical velocity, nutrient anomaly, and phytoplankton anomaly are a measure of the flux, which relates to the total production. We examine these co-variances in both an Eulerian and Lagrangian frame. In addition to altering the magnitude of the nutrient and phytoplankton anomalies, the phytoplankton growth rate modulates the phase of the relationship between the vertical velocity, nutrient, and phytoplankton anomalies. The spatial relationship between physical upwelling, new production, and phytoplankton concentration in the ocean can be obscure, and depends on the interplay between the physical and biological time scales.