delta C-13 analyses of individual lignin phenols in Quaternary lake sediments: A novel proxy for deciphering past terrestrial vegetation changes

This study of the sediments from Sacred Lake, Mount Kenya, demonstrates tha t delta(13)C analyses of individual lignin phenols can be used to assess pa st changes in the proportion of C-3 and C-4 plants within different plant g roups in the lake catchment. Vegetation changes resulting from climatic and atmospheric changes since the last glacial maximum can be deduced from spe cific lignin phenols. Lignin, a major biopolymer in vascular plants, differ s from n-alkyl lipids in (1) its higher specificity and more quantitative r epresentation of vascular-plant input and (2) its major transport mechanism into the sediments by fluvial runoff, as opposed to the greater importance of eolian transport for leaf waxes and pollen. Lignin delta(13)C data supp ort the hypothesis that atmospheric CO2 concentration is an important facto r controlling the vegetation in tropical mountain ecosystems, and provide a dditional insights into past changes in vegetation structure, Specifically, the delta(13)C values of p-coumaric acid indicate the persistence of C-4 g rasses during the late glacial, when the lake level was lower than today, s uggesting that aridity also played a role in controlling the abundance of C -4 plants.