Julio L. Betancourt Steven W. Leavitt Elise Pendall 1999 <p>We compared two approaches to interpreting &delta;D of cellulose nitrate in pi&ntilde;on pine needles (<i>Pinus edulis</i>) preserved in packrat middens from central New Mexico, USA. One approach was based on linear regression between modern &delta;D values and climate parameters, and the other on a deterministic isotope model, modified from Craig and Gordon's terminal lake evaporation model that assumes steady-state conditions and constant isotope effects. One such effect, the net biochemical fractionation factor, was determined for a new species, pi&ntilde;on pine. Regressions showed that &delta;D values in cellulose nitrate from annual cohorts of needles (1989&ndash;1996) were strongly correlated with growing season (May&ndash;August) precipitation amount, and &delta;¹³C values in the same samples were correlated with June relative humidity. The deterministic model reconstructed &delta;D values of meteoric water used by plants after constraining relative humidity effects with &delta;¹³C values; growing season temperatures were estimated via modern correlations with &delta;D values of meteoric water. Variations of this modeling approach have been applied to tree-ring cellulose before, but not to macrofossil cellulose, and comparisons to empirical relationships have not been provided. Results from fossil pi&ntilde;on needles spanning the last &sim;40,000 years showed no significant trend in &delta;D values of cellulose nitrate, suggesting either no change in the amount of summer precipitation (based on the transfer function) or &delta;D values of meteoric water or temperature (based on the deterministic model). However, there were significant differences in &delta;¹³C values, and therefore relative humidity, between Pleistocene and Holocene.</p> application/pdf 10.1016/S0031-0182(98)00152-7 en Elsevier Paleoclimatic significance of δD and δ¹³C values in pinon pine needles from packrat middens spanning the last 40,000 years article