Abstract
Abstract. A bell-shaped vertical profile of chlorophyll a (Chl a) concentration, conventionally referred to as a subsurface chlorophyll maximum (SCM) phenomenon, has frequently been observed in stratified oceans and lakes. This profile is assumed to be a general Gaussian distribution in this study. By substituting the general Gaussian function into ecosystem dynamical equations, the steady-state solutions for SCM characteristics (i.e., SCM layer depth, thickness, and intensity) in various scenarios are derived. These solutions indicate that (1) the maximum concentration of Chl a occurs at or below the depth of maximum growth rates of phytoplankton located at the transition from nutrient limitation to light limitation, and the depth of SCM layer deepens logarithmically with an increase in surface light intensity; (2) thickness and intensity of the SCM layer are mainly affected by nutrient supply, but independent of surface light intensity; and (3) intensity of the SCM layer is proportional to the diffusive flux of nutrients from below, which becomes stronger as a result of this layer being shrunk by a higher light attenuation coefficient or a larger sinking velocity of phytoplankton. In addition, the limitation and potential application of the analytical solutions are also presented.
Highlights
Vertical profiles of chlorophyll a (Chl a) concentration in lakes, coastal seas, and open oceans are highly variable
The SCM layer (SCML) occurs below the surface mixed layer, where the light attenuated from above and nutrients supplied from the deep water result in the maximal value of phytoplankton growth rate (Fig. 1)
We investigate how the steady-state thickness, depth, and intensity of SCML depend on environmental parameters
Summary
Vertical profiles of chlorophyll a (Chl a) concentration in lakes, coastal seas, and open oceans are highly variable. A bell-shaped vertical profile of Chl a, conventionally referred to as a subsurface chlorophyll maximum (SCM). Phenomenon, has been frequently observed in stratified water columns; for example, it occurs through the whole year in tropical and subtropical oceans, while it exists only during summer in temperate and high-latitude oceanic zones. The subsurface biomass maxima (SBMs) are common in stratified water columns. The chlorophyll-to-biomass ratio generally increases with depth in the euphotic zone. The subsurface maxima in both chlorophyll and biomass are usually formed in certain regions of the water column where two opposing resource (light and nutrient) gradients combined with turbulent mixing are amenable for survival of phytoplankton. SCMs are approximately equal to SBMs in many studies (Klausmeier and Litchman, 2001; Sharples et al, 2001; Huisman et al, 2006; Raybov et al, 2010). Fennel and Boss (2003) reported that the photoacclimation of phytoplankton can be another important reason for forming an SCM in oligotrophic waters
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