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

Stable carbon isotope measurements (δ¹³C) made on Quaternary sequences of terrestrial plant subfossils are frequently used to infer palaeoclimatic trends. However, differential decomposition of individual constituents during incorporation of plant material into lake sediments could influence these interpretations. Therefore, 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 both δ¹³C 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 δ¹³C 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 determined 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.