Variability in the chlorophyll‐specific absorption coefficients of natural phytoplankton: Analysis and parameterization

TLDR

The observed covariation between a ph * (λ) and field chlorophyll‑a concentration can be explained by pigment packaging and accessory pigment absorption. These relationships enable the generation of a ph * spectrum as a function of mean chlorophyll concentration. The authors analyzed 815 wet‑filter spectra from the global ocean and derived power‑law relationships between a ph * (λ) and mean chlorophyll concentration. Absorption coefficients decrease with increasing chlorophyll, spanning more than an order of magnitude, and the resulting parameterization could refine global carbon‑fixation estimates when combined with satellite pigment maps and production models.

Abstract

Variability in the chlorophyll (chl) a ‐specific absorption coefficients of living phytoplankton a ph * (λ) was analyzed using a data set including 815 spectra determined with the wet filter technique in different regions of the world ocean (covering the chlorophyll concentration range 0.02–25 mg m −3 ). The a ph * values were observed to decrease rather regularly from oligotrophic to eutrophic waters, spanning over more than 1 order of magnitude (0.18 to 0.01 m 2 mg −1 ) at the blue absorption maximum. The observed covariation between a ph * (λ) and the field chl a concentration (chl) can be explained considering (1) the level or pigment packaging and (2) the contribution of accessory pigments to absorption. Empirical relationships between a ph * (λ) and 〈chl〉 were derived by least squares fitting to power functions. These relationships can be used to produce a ph * spectra as a function of 〈chl〉. Such a simple parameterization, if confirmed with further data, can be used, e.g., for refining estimates of the carbon fixation rate at global or regional scales, such as those obtained by combining satellite pigment concentration maps with primary production models based on physiological parameters, among which a ph * is an important one.