Diversity of growth rates maximizes phytoplankton productivity in an eddying ocean

TL;DR

This study demonstrates that phytoplankton productivity in eddying oceans is maximized when growth rates align with vertical motion timescales, promoting community diversity and higher overall productivity.

Contribution

It reveals how the interplay between phytoplankton growth rates and vertical nutrient flux controls productivity and fosters community diversity in submesoscale ocean dynamics.

Findings

Optimal growth rate of 1/3 day$^{-1}$ maximizes productivity.

Vertical flux depends nonlinearly on growth rate and flow dynamics.

Diversity in growth rates enhances overall phytoplankton productivity.

Abstract

In the subtropical gyres, phytoplankton rely on eddies for transporting nutrients from depth to the euphotic zone. But, what controls the rate of nutrient supply for new production? We show that vertical nutrient flux depends both on the vertical motion within the eddying flow and varies nonlinearly with the growth rate of the phytoplankton itself. Flux is maximized when the growth rate matches the inverse of the decorrelation timescale for vertical motion. Using a three-dimensional ocean model and a linear nutrient uptake model, we find that phytoplankton productivity is maximized for a growth rate of 1/3 day$^{-1}$, which corresponds to the timescale of submesoscale dynamics. Variability in the frequency of vertical motion across different physical features of the flow favors phytoplankton production with different growth rates. Such a growth-transport feedback can generate diversity in the phytoplankton community structure at submesoscales and higher net productivity in the presence of community diversity.