Amount-weighted annual isotopic (δ18O) values are affected by the seasonality of precipitation:: A sensitivity study

Year to year differences in the isotopes of precipitation (delta O-18) are typically attributed to corresponding interannual changes in mean annual temperature. However, changes in the seasonal distribution of precipitation are one of the main complicating factors in interpreting year to year variability of isotopes of precipitation. Using a five year dataset with 73 sites across the United States, we investigate the influence of changes in seasonal distribution of precipitation on annually averaged delta O-18. Based on these delta O-18 measurements, and using multi-decadal records of variability of monthly precipitation amounts, we identify areas within the United States where records of isotopes in precipitation are susceptible to changes in the seasonal distribution of precipitation. For the three regions, Northern Great Plains, the Rocky Mountains, and the Southwest, seasonality effects could be misinterpreted as 1 degrees C to 3 degrees C temperature changes between years. These findings will improve and possibly change our interpretation of climate isotopic climate records and provide spatially explicit areas where classic interpretations require caution.