Methodology for use of isotopic climate forcings in ice sheet models.

In ice sheet models, an internally consistent calculation of climatic tempe rature forcing from ice-core isotopic records (delta) requires that correct ions be made for an ice core site's elevation changes. Such corrections can be important for two reasons. First, elevation change at an ice divide can be large compared to elevation change at the migrating ice margin, resulti ng in erroneous estimates of marginal melt rate. Second, the delta of preci pitation at an ice divide responds less to regional climatic temperature ch anges than to local temperature changes of the same magnitude that are caus ed by elevation changes. Significant elevation-change corrections may also be necessary for inferring the relationships used to calculate climatic tem perature from delta. A simple methodology incorporating both of these eleva tional effects is presented here. Further, I recommend that the delta to te mperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and delta time-series rather than f rom spatial correlations, and justify this recommendation based on current understanding of the atmospheric isotopic distillation system.