Variations in the carbon isotope composition of late-Holocene plant macrofossils: a comparison of whole-leaf and cellulose trends

Abstract

Stable carbon isotope measurements (δ13C) made on Quaternary sequences of terrestrial plant subfos sils are frequently used to infer palaeoclimatic trends. However, differential decomposition of individual con stituents during incorporation of plant material into lake sediments could influence these interpretations. There fore, we investigated down-core variations in the carbon isotope composition (δ13C) of subfossil leaves of Salix herbacea L., and their holocellulose component, from a late-Holocene ( c. 0–3300 years ago) site in northern Sweden. Locally weighted regression curves fitted to bothδ13C data sets showed similar but conserved temporal patterns of change, and there was no evidence for systematic shifts in the holocellulose yields or C:N ratios of leaves with age. Small d13C variations over the past 3300 years probably reflect natural variations in microclimate within the lake catchment area. This interpretation is quantitatively consistent with the variability determ ined from measurements made on leaves of modern S. herbacea plants growing at the same site. Overall these results imply that, under conditions of uniform decomposition,δ13C measurements made on late-Holocene sequences of whole leaves provide an interpretation of the pattern and direction of change consistent with that obtained from holocellulose isolated from the same leaves.