Measurement and interpretation of sedimentary pigments

Abstract

SUMMARY. The factors that control the concentrations of pigments in lake sediments are examined using data from (i) transects across lake basins, (ii) surface samples from logographic and atrophic lakes, and (iii) two 210Pb‐dated short cores. Methods for the rapid non‐chromatographic analysis of percent native chlorophyll and the blue‐green algal pigments oscillaxanthin and myxoxanthophyll are described. The concentrations of chlorophyll derivatives, total arytenoids, oscillaxanthin and myxoxanthophyll, and percent native chlorophyll, are higher under conditions along the transects favorable for preservation. Chlorophyll degrades at about the same rate as total carotenoids, and oscillaxanthin degrades at about the same rate as myxoxanthophyll. Therefore, both the ratio of chlorophyll to arytenoids (CD/TC) and the ratio of oscillaxanthin to myxoxanthophyll (OSC/MYX) are mostly determined by the quality of autochthonous production rather than by preservation conditions. CD/TC values are higher in logographic lakes than in atrophic lakes, apparently as a result of differences in production of the two pigment types. Calculations show that CD/TC shifts in these two cores cannot be a record of the allochthonous‐autochthonous Baltic in the systems. Instead, the CD/TC values shift with large changes in the kinds of plants dominating primary production. The stratigraphy of percent native chlorophyll appears to record the hypohmnetic oxygen concentrations at the time of deposition. No obvious reason exists why a eutrophic lake should produce more pigment per gram organic matter than should an oligotrophic lake. However, several correlated mechanisms tend to produce higher sedimentary pigment concentrations in eutrophic lakes. Most of these mechanisms, such as hypolimnetic oxygen consumption, indirectly translate greater primary productivity into greater sedimentary pigment concentration. Therefore, pigment concentrations are sometimes misleading, and pigment accumulation rate may be a better indicator of past primary production.