A century-scale record of the preservation of chlorophyll and its transformation products in anoxic sediments

We have determined the chlorophyll pigment composition by liquid chromatography (LC) and LC/MS/MS in a 1.45-m long freeze core, representing 157 years of annually varved sedimentation, from Saanich Inlet, B.C, Canada. We investigated the very early diagenetic processes of chlorophyll a alteration in these anoxic sediments and the possible implications for palaeoproductivity studies. Excellent preservation of pigments is indicated by high total pigment concentrations, and the presence of labile compounds such as chlorophyllide a. The lack of systematic down core changes in both the total pigment concentration and the chlorin composition indicates that no detectable alteration of the pigment composition has occurred during the past 157 years. The sedimentary pigment composition is the result of processes occurring in the water column, or within few months after deposition. Chlorophyll derivatives corresponding to different diagenetic processes have distinct down core profiles. Profiles of compounds related to grazing activity steryl pyrophaeophorbide esters (SPE) and pyrophaeophytin a, are very similar. In contrast, dephytylated compounds (chlorophyllide a and phaeophorbide a), which are related to chlorophyllase activity during the degradation of ungrazed diatom cells, show an independent pattern. Quantifying pigment composition in Saanich Inlet sediments can help constrain processes regarding the transport of algal pigments to the sediments. Copyright (C) 2000 Elsevier Science Ltd.