C-13 DISCRIMINATION BY FOSSIL LEAVES DURING THE LATE-GLACIAL CLIMATE OSCILLATION 12-10 KA BP - MEASUREMENTS AND PHYSIOLOGICAL CONTROLS

The late-glacial climatic oscillation, 12-10 ka BP, is characterised i n ice core oxygen isotope profiles by a rapid and abrupt return to gla cial climate. Recent work has shown that associated with this cooling was a drop in atmospheric CO2 concentration of ca. 50 ppm. In this pap er, the impact of these environmental changes on C-13 discrimination i s reported, based on measurements made on a continuous sequence of fos sil Salix herbacea leaves from a single site. The plant responses were interpreted using an integrated model of stomatal conductance, CO2 as similation and intercellular CO2 concentration, influenced by external environmental factors. According to the model, temperature exerts a m arked influence on C-13 discrimination by leaves and the pattern of C- 13 changes recorded by the fossil leaves is consistent with other pala eotemperature curves for 12-10 ka BP, particularly the deuterium isoto pe record from Alaskan Salix woods, which generally reflects ocean tem peratures. The gas exchange model correctly accounts for these changes and so permits the reconstruction of ancient rates of leaf CO2 uptake and loss of water vapour in response to the abrupt late-glacial chang es in global climate and CO2. The approach provides the required physi ological underpinning for extracting quantitative estimates of past te mperatures and for contributing an ecophysiological explanation for ch anges in C-13 discrimination in the fossil record.