01 Dec 2020

01 Dec 2020

Review status: this preprint is currently under review for the journal BG.

An investigation of grazing behaviors that result in winter phytoplankton biomass accumulation

Mara Freilich1, Alexandre Mignot2, Glenn Flierl3, and Raffaele Ferrari3 Mara Freilich et al.
  • 1MIT-WHOI Joint Program in Oceanography & Applied Ocean Science and Engineering, Cambridge, MA, USA
  • 2Mercator Ocean International, Ramonville-Saint-Agne, France
  • 3Department of Earth Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA

Abstract. Recent observations have shown that phytoplankton biomass increases in the North Atlantic during winter, even when the mixed layer is deepening and light is limited. Current theories suggest that this is due to a release from grazing pressure. Here we demonstrate that the often-used grazing models that are linear at low phytoplankton concentration do not allow for a wintertime increase in phytoplankton biomass. However, certain mathematical formulations of grazing that are quadratic (or more generally non-linear) in phytoplankton concentration at low concentrations can reproduce the fall to spring transition in phytoplankton, including wintertime biomass accumulation. We illustrate this point with a minimal model for the annual cycle of North Atlantic phytoplankton designed to simulate phytoplankton concentration as observed by BioGeoChemical-Argo (BGC-Argo) floats in the North Atlantic. This analysis provides a mathematical framework for assessing hypotheses of phytoplankton bloom formation.

Mara Freilich et al.

Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Mara Freilich et al.

Model code and software

Grazing functions and winter phytoplankton accumulation Mara Freilich

Mara Freilich et al.


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Short summary
Observations reveal that in some regions phytoplankton biomass increases during the wintertime when growth conditions are sub-optimal, which has been attributed to a release from grazing during mixed layer deepening. Measurements of grazer populations to support this theory are lacking. We demonstrate that a release from grazing when the winter mixed layer is deepening holds only for certain grazing models, extending the use of phytoplankton observations to make inferences about grazer dynamics.