Environmental controls on pigment distributions in the freshwater microbialites of Fayetteville Green Lake

Pigments in acetone extracts of microbialites collected over a shallow depth gradient from the freshwater Fayetteville Green Lake (FGL), Fayetteville, NY were analyzed. Pigment identifications and quantification were achieved using reverse phase high performance liquid chromatography and ion trap multi-stage mass spectrometry (MSⁿ). Chlorophyll a and its derivatives, the photoprotective pigment scytonemin and the carotenoid, fucoxanthin, were present in all samples; β-carotene was observed in all but one sample and minor abundances of other pigments, such as chlorophyll d and lutein, were observed in selected samples. The concentration of scytonemin and its abundance relative to that of chlorophyll a decreased logarithmically with depth, consistent with the function of scytonemin as a UV screening pigment. The increase in the concentration of chlorophylls a, b and the photosynthetic accessory carotenoids, fucoxanthin and β-carotene with depth, are consistent with the lower irradiance at depth. The distribution and relative abundances of photosynthetic and light shielding pigments may provide a means for determining the relative water depth/incident radiation levels of ancient microbialites in which pigments or their derivatives are preserved.