Fitting vertical chlorophyll profiles in the California Current using two Gaussian curves

Abstract

Vertical distribution of chlorophyll a (Chla) in the euphotic zone has been described and modeled by a Gaussian curve representing those cases where there is a single Chla maximum (surface or subsurface). This has led to the rejection of profiles with more than one chlorophyll peak, resulting in the removal of up to 18% of the profiles. The aim of this article is to propose an alternative equation to fit vertical Chla profiles, including those with two maxima in the euphotic zone. A total of 315 vertical profiles of Chla from the 2011 CALCOFI four-cruise series in the California Current were evaluated. Since Chla profiles show various shapes, it was decided to try four models: single Gaussian curve (single maximum) with and without gradient and double Gaussian curves (two maxima) also with and without gradient, which were fitted using Genetic Algorithms. The model that fitted Chla profiles best was the double maximum with gradient model, which is the one with the lowest root mean square error and was able to fit almost all Chla profiles in the CalCoFi area. This model has the ability to fit the vertical chlorophyll profiles with one or two maxima, including those that occur with a gradient with depth. Although the models were tested using data from the California Current, we recommend using the model in other ocean regions where double chlorophyll maximums occur.