The oxygen isotope value of whole wood, ?-cellulose, and holocellulose in modern and fossil wood

The oxygen isotope value (delta 18O) of alpha-cellulose extracted from modern and fossil wood has been used widely to reconstruct climate throughout the Quaternary and deep-time. Substantial effort has been made towards developing more efficient and cost-effective methods for obtaining alpha-cellulose from whole wood, though some research groups advocate for measuring delta 18O directly on whole wood due to a constant offset between the delta 18O of whole wood and alpha-cellulose. The utility of alternative substrates to alpha-cellulose (e.g., whole wood or hol-ocellulose) for paleoclimate reconstruction using fossil wood, however, has not been evaluated. Here we present 48 new delta 18O measurements on mummified (subfossil) wood ranging in age from Eocene to Miocene. Whereas the delta 18O value of whole wood and alpha-cellulose is only weakly related in these subfossils, there is a strong linear correlation between the delta 18O value of alpha-cellulose and holocellulose. We augmented this dataset with 1546 new and published oxygen isotope pairs on whole wood, alpha-cellulose, and holocellulose from modern wood (Qua-ternary to present) to compare with our pre-Quaternary fossil samples. In contrast to the fossil wood, we found strong correlations between alpha-cellulose and whole wood and alpha-cellulose and holocellulose in modern samples. This finding suggests that all three substrates (whole wood, cellulose and holocellulose) derive oxygen isotopes from a common source (i.e., meteoric water) on a global scale, and that processing of alpha-cellulose may not be required for modern wood in some settings. Because average holocellulose yields in fossil wood were approxi-mately double that of alpha-cellulose (22.2 +/- 12.8% versus 11.6 +/- 10.3%), delta 18O analysis on holocellulose rather than alpha-cellulose should produce reliable environmental data while reducing time and sample material required.