On the temperature correlation of δ18O in modern precipitation

Reevaluation of modern precipitation, temperature, and isotope data permits reconciliation of previous disparate values for the correlation between δ18O of modern precipitation and surface temperature. Past analysis has used the mean surface temperature over the time interval of sample collection (e.g., mean weekly, monthly, or annual temperature) to calculate temperature coefficients, and different approaches at mid-latitudes yield different temperature coefficients (Δδ18O/ΔT): spatial correlations among geographically distinct sites yield ∼0.55‰/K; seasonal variations at single sites yield 0.2-0.4‰/K; and 12 month running averages yield 0.5-1‰/K. However, there are systematic differences in temperature during precipitation events vs. time-averaged surface temperature means. Correction for this bias using hourly weather and monthly isotope data from U.S. sites yields a single value of ∼0.55‰/K for all three approaches. Revised temperature coefficients based on surface observations are also commensurate with coefficients obtained using cloud base temperatures and with theoretical distillation models (0.5-0.7‰/K). These coefficients provide a consistent basis for validation of general circulation models that incorporate stable isotopes of precipitation, and for comparison to independent estimators of the isotopic response to climate change.