Abstract
Abstract. Here we show a simple mechanism in which changes in the rate of horizontal stirring by mesoscale ocean eddies can trigger or suppress plankton blooms and can lead to an abrupt change in the average plankton density. We consider a single species phytoplankton model with logistic growth, grazing and a spatially non-uniform carrying capacity. The local dynamics have multiple steady states for some values of the carrying capacity that can lead to localized blooms as fluid moves across the regions with different properties. We show that for this model even small changes in the ratio of biological timescales relative to the flow timescales can greatly enhance or reduce the global plankton productivity. Thus, this may be a possible mechanism in which changes in horizontal mixing can trigger plankton blooms or cause regime shifts in some oceanic regions. Comparison between the spatially distributed model and Lagrangian simulations considering temporal fluctuations along fluid trajectories, demonstrates that small scale transport processes also play an important role in the development of plankton blooms with a significant influence on global biomass.
Highlights
In the open ocean, the dynamics of phytoplankton ecosystems are strongly influenced by the physical characteristics of the environment
We have demonstrated that the dynamics of phytoplankton blooms can be affected by www.nonlin-processes-geophys.net/16/623/2009/
We show that the existence of a bloom is sensitive to the ratio of biological and hydrodynamical time scales (γ ), highlighting the importance of horizontal ocean advection in the generation of plankton blooms
Summary
The dynamics of phytoplankton ecosystems are strongly influenced by the physical characteristics of the environment. One typical example of such a regime shift is eutrophication in shallow lakes, where increased phosphorus concentration in the lake may lead to an abrupt rise of some phytoplankton densities, which suppress submerged plants and zooplankton and fish populations (Scheffer, 1990; Scheffer et al, 1993, 2001). Another example of harmful blooms are red tide events, associated with high concentrations of the phytoplankton species Karenia brevis, usually occurring in coastal areas (Yentsch et al, 2008)
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