# The effect of intermittent upwelling events on plankton blooms

## TL;DR

This study investigates how intermittent nutrient upwelling events influence plankton blooms, revealing that the hydrodynamic flow structure critically determines whether nutrients promote harmful algal blooms or are washed away.

## Contribution

It demonstrates that the response of plankton to nutrient pulses depends on mesoscale flow dynamics, explaining the variability in bloom formation and observational inconsistencies.

## Key findings

- Nutrient upwelling can either trigger blooms or be washed out.
- Flow vortices determine nutrient retention or dispersal.
- Predicting HABs requires understanding flow-nutrient interactions.

## Abstract

In the marine environment biological processes are strongly affected by oceanic currents, particularly by eddies (vortices) formed by the hydrodynamic flow field. Employing a kinematic flow field coupled to a population dynamical model for plankton growth, we study the impact of an intermittent upwelling of nutrients on triggering harmful algal blooms (HABs). Though it is widely believed that additional nutrients boost the formation of HABs or algal blooms in general, we show that the response of the plankton to nutrient plumes depends crucially on the mesoscale hydrodynamic flow structure. In general nutrients can either be quickly washed out from the observation area, or can be captured by the vortices in the flow. The occurrence of either scenario depends on the relation between the time scales of the vortex formation and nutrient upwelling as well as the time instants at which upwelling pulse occurs and how long do they last. We show that these two scenarios result in very different responses in plankton dynamics which makes it very difficult to predict, whether nutrient upwelling will lead to a HAB or not. This explains, why observational data are sometimes inconclusive establishing a correlation between upwelling events and plankton blooms.