ATMOSPHERIC CO2 CHANGES SINCE THE LAST GLACIAL MAXIMUM - EVIDENCE FROM THE STOMATAL DENSITY RECORD OF FOSSIL LEAVES

It has been shown that a strong negative correlation exists between st omatal density and atmospheric CO2 concentration in the leaves of deci duous temperate forest trees. This correlation was initially establish ed on a time scale of some 200 years, using dated leaf specimens from herbaria, and confirmed by experimental observations under controlled CO2 levels. In the present investigation we have attempted to combine the use of fossil-leaves with the long-term ice core record of CO2 cha nges to extend the time scale of stomatal density response to CO2 chan ge. Stomatal counts were made from fossil leaves of the dwarf willow S alix herbacea spanning the last glacial cycle, and we are able to demo nstrate a reduction in density in response to increased CO2. This rela tionship is used to reconstruct the pattern of CO2 change since the la st glacial maximum. The results are compared with the Byrd ice core re cord from Antarctica. The pattern of CO2 change in both records is rem arkably similar, although there is some mis-match on the dating of cer tain features of these patterns. We suggest that this method of CO2 re construction may be developed further to extend the use of stomatal de nsity studies to elucidate atmospheric CO2 trends during earlier criti cal phases of the Earth's history, long pre-dating the ice core record .