Hyperspectral variability of photosynthetically active radiation experienced by phytoplankton in the oceanic surface mixed layer

Abstract

The relevance of marine phytoplankton as a food for the pelagos and as a potential sink of atmospheric carbon is widely recognised. Their physiological response to photosynthetically active radiation (PAR) not only depends on the light intensity but also on the variability of PAR over short to medium time scales. Most phytoplankton are passively mixed in the oceanic mixing layer by turbulence, with vertical mixing being the crucial component which determines light variability. In this contribution, we use results from a 3D particle tracking model to analyse the light histories of phytoplankton cells in a range of oceanic environments. The vertical displacement is calculated from a k-e turbulence model, and the light availability at each cell¿s location is determined through Hydrolight. The results show the amount of PAR variability experienced by phytoplankton populations and its effect on phytoplankton growth for a range of optical depths of the mixing layer and for a range of mixing intensities. Our results illustrate the importance of accounting for this short term variability when attempting to estimate primary production in the mixing layer (e.g. from incubation experiments or from satellite imagery)