Fossil pigments in paleoecology and paleolimnology

Abstract

For the past several decades scientists have been examining the nature of sedimentary chlorophylls and carotenoids from freshwater lakes for their value in paleoecology and paleolimnology. Unaltered chlorophyll molecules are rarely preserved for long periods, but the pheo-derivatives and chlorophyllides are common throughout lake sedimentary columns. Carotenoids tend to preserve largely unaltered from their conditions in living plant membranes, but degrade quickly to colorless derivatives when oxidized. Measurements of sedimentary pigment concentrations, ratios of chlorophyll derivatives to carotenoids and diversity, especially as regards prokaryote carotenoids, are most commonly published. This paper assesses the value of using sedimentary pigment data to provide paleoecological information on lake evolution and changing patterns of aquatic primary productivity. Factors that promote pigment preservation are contrasted to those that alter and cause destruction of organic molecules. The value of fossil pigments is considered in ascertaining the sources of organic matter to sediments and for providing clues to the changing diversity of aquatic flora, both rooted and planktonic. Consideration is given to recent investigations that have sought information from sedimentary pigments on the onset and intensity of cultural eutrophication, both in individual lakes and on a regional basis, and in the monitoring of progress toward lake restoration. A special case is made for the value of sampling meromictic lakes. In addition, this review provides information on the limitations of the sampling procedures, laboratory techniques, and interpretation of results, Discussion is made of the most valuable and easily obtainable data that can provide reliable, comparable and reproducible results. Special consideration is given to the value of the pigment data in supplementing additional paleoecological indicators such as sedimentary pollen grains, zooplankton, and various other sedimentary bio- and geochemical products.