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Synoptic and Mesoscale Mechanisms Drive Winter Precipitation δ 18 O/δ 2 H in South‐Central Alaska
Author(s) -
Bailey Hannah L.,
Klein Eric S.,
Welker Jeffrey M.
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd030050
Subject(s) - mesoscale meteorology , precipitation , air mass (solar energy) , arctic , zonal and meridional , climatology , stable isotope ratio , atmospheric sciences , environmental science , geology , meteorology , geography , oceanography , physics , boundary layer , quantum mechanics , thermodynamics
Abstract Measurements of oxygen and hydrogen stable isotopes in precipitation (δ 18 O P and δ 2 H P ) provide a valuable tool for understanding modern hydrological processes and the empirical foundation for interpreting paleoisotope archives. However, long‐term data sets of modern δ 18 O P and δ 2 H P in southern Alaska are entirely absent, thus limiting our insight and application of regionally defined climate‐isotope relationships in this proxy‐rich region. We present and utilize a 13‐year‐long record of event‐based δ 18 O P and δ 2 H P data from Anchorage, Alaska (2005–2018, n = 332), to determine the mechanisms controlling precipitation isotopes. Local surface air temperature explains ~30% of variability in the δ 18 O P data with a temperature‐δ 18 O slope of 0.31 ‰/°C, indicating that δ 18 O P archives may not be suitable paleo‐thermometers in this region. Instead, back‐trajectory modeling reveals how winter δ 18 O P /δ 2 H P reflects synoptic and mesoscale processes in atmospheric circulation that drive changes in the passage of air masses with different moisture sources, transport, and rainout histories. Specifically, meridional systems—with either northerly flow from the Arctic or southerly flow from the Gulf of Alaska—have relatively low δ 18 O P /δ 2 H P due to progressive cooling and removal of precipitation as it condenses with altitude over Alaska's southern mountain ranges. To the contrary, zonally derived moisture from either the North Pacific and/or Bering Sea retains relatively high δ 18 O P /δ 2 H P values. These new data contribute a better understanding of the modern Alaska water isotope cycle and provide an empirical basis for interpreting paleoisotope archives in context of regional atmospheric circulation.