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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L21707, doi:10.1029/2007GL030547, 2007

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

R. W. Vachon

Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA


J. W. C. White

Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA


E. Gutmann

Center for the Study of Earth from Space and Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado, USA


J. M. Welker

Environment and Natural Resources Institute and Biology Department, University of Alaska Anchorage, Alaska, USA


Abstract

Year to year differences in the isotopes of precipitation (δ 18O) 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 δ 18O. Based on these δ 18O 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°C to 3°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.

Received 1 May 2007; accepted 8 October 2007; published 15 November 2007.

Keywords: precipitation; stable isotopes; climate change.

Index Terms: 1041 Geochemistry: Stable isotope geochemistry (0454, 4870); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3354 Atmospheric Processes: Precipitation (1854); 3344 Atmospheric Processes: Paleoclimatology (0473, 4900); 3333 Atmospheric Processes: Model calibration (1846).

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Citation: Vachon, R. W., J. W. C. White, E. Gutmann, and J. M. Welker (2007), Amount-weighted annual isotopic (δ18O) values are affected by the seasonality of precipitation: A sensitivity study, Geophys. Res. Lett., 34, L21707, doi:10.1029/2007GL030547.