Lignin geochemistry of a Late Quaternary sediment core from Lake Washington

Abstract Long-term lignin stability and paleovegetation patterns were investigated using CuO oxidation products of sediments from an 11 m core of Late Quaternary sediment collected from the mid-basin of Lake Washington, Washington State. Relatively constant yields of lignin-derived phenols (normalized to organic carbon) from the entire core indicate minimal in situ lignin degradation over the last 13,000 years. Compositional patterns within the phenolic suite and increased corresponding yields from baseextracted sediments indicate that sedimentary lignins are present predominantly as well preserved plant tissue fragments. Abundance patterns of vanillyl, syringyl, and cinnamyl phenols record four distinct sequences within the core characterized by: 1. (a) high concentrations of gymnosperm wood in a basal horizon of glacial flour, 11-10 m; 2. (b) an essentially pure mixture of nonwoody angiosperm tissues in late Pleistocene sediments, 10-8 m; 3. (c) relatively high concentrations of angiosperm woods in the bottom half of a limnic peat sequence deposited approximately 10,000–7,000 years B.P., 8-4 m; and 4. (d) a progressive enrichment in gymnosperm woods at the expense of angiosperm woods over the last 7,000 years in the upper limnic peat, 4-0 m. Vascular plant tissues account for less than half the total sedimentary organic carbon throughout the core.