Lake paleoenvironment indicated by sedimentary photosynthetic pigments

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1. Profiles of photosynthetic pigments of phytoplankton (algae) in sediment cores of Lake Baikal and Hovsgol representing the last 〜25,000 years revealed increase in the lake primary productivity through the last glacial/post glacial transition.2. Steryl chlorin esters (SCEs) derived from chlorophylls (Chls) were shown to be actually a sole group of the sedimentary pigments in the 0-200 m portion of a long sediment core from central Lake Baikal, the BDP98 core, representing the last 5 Ma. Thus SCEs a derived from Chl a common in algae serves as an indicator of long-term trend of primary production in the lake, while SCEs b derived from Chl b indicates green algae and C_<30>-sterol-SCE a dinoflagellates. The periods of SCEs a minima well correspond to those of even-numbered marine oxygen isotope stage (MIS), that is, those of ice-sheet development in the northern hemisphere. Accordingly, global climate changes have been a primary factor controlling the algal productivity in the lake. The periods when relative abundance of green algae and dinoflagellates were large correspond to the first (260 Ma) and second (150 Ma) cooling periods of this region.3. SCE composition found in fecal pellets egested from crustaceans fed on algae in laboratory gave key information on the composition of sedimentary SCEs.4. In a sediment cores obtained from central Lake Hamana, which represents the last 〜250 years, in addition to the algal photosynthetic pigments, those of sulfur bacteria live in anoxic water were found, indicating the occurrence of anoxia through the period. The period of indicated proliferation of purple sulfur bacteria in the late 1930s is consistent with that reported in literatures. The trend in the development of anoxic water layers indicated by the pigments and Mo is strongly influenced by the training wall constructed at the Imagireguchi channel causing increase of the seawater intrusion into the lake.