Phytoplankton patchiness: quantifying the biological contribution using Fast Repetition Rate Fluorometry

The coupling between physical and biological processes is important in the marine environment because phytoplankton growth and turbulent miring operate on similar time scales. Since the 1970s, the relative contribution of these two parameters to phytoplankton patchiness has been studied using analytical tools such as spectral analysis. Here, for the first time, we combine spectral analysis with Fast Repetition Rate Fluorometry as a method of quantifying the importance of photosynthetic efficiency in the biological-physical interactions that lead to oceanic chlorophyll distributions. The results indicate that photosynthetic efficiency is correlated with the sum of the corresponding chlorophyll power spectrum; a measure of the total spatial variability of chlorophyll. In addition, high photosynthetic rates are associated with regions where the spatial distributions of chlorophyll and salinity differ, as quantified by the slopes of their respective power spectra. The results are particularly evident at large spatial scales, representing an empirical verification of previous theoretical work regarding phytoplankton spatial structure.