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Modeling insights into deuterium excess as an indicator of water vapor source conditions
Author(s) -
Lewis Sophie C.,
LeGrande Allegra N.,
Kelley Maxwell,
Schmidt Gavin A.
Publication year - 2013
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2012jd017804
Subject(s) - paleoclimatology , deuterium , proxy (statistics) , atmospheric sciences , environmental science , climatology , δ18o , tracer , water vapor , humidity , geology , stable isotope ratio , climate change , thermodynamics , meteorology , oceanography , physics , quantum mechanics , machine learning , computer science , nuclear physics
Deuterium excess ( d ) is interpreted in conventional paleoclimate reconstructions as a tracer of oceanic source region conditions, such as temperature, where precipitation originates. Previous studies have adopted coisotopic approaches (using both δ 18 O and d ) to estimate past changes in both site and oceanic source temperatures for ice core sites using empirical relationships derived from conceptual distillation models, particularly Mixed Cloud Isotopic Models (MCIMs). However, the relationship between d and oceanic surface conditions remains unclear in past contexts. We investigate this climate‐isotope relationship for sites in Greenland and Antarctica using multiple simulations of the water isotope‐enabled Goddard Institute for Space Studies ModelE‐R general circulation model and apply a novel suite of model vapor source distribution (VSD) tracers to assess d as a proxy for source temperature variability under a range of climatic conditions. Simulated average source temperatures determined by the VSDs are compared to synthetic source temperature estimates calculated using MCIM equations linking d to source region conditions. We show that although deuterium excess is generally a faithful tracer of source temperatures as estimated by the MCIM approach, large discrepancies in the isotope‐climate relationship occur around Greenland during the Last Glacial Maximum simulation, when precipitation seasonality and moisture source regions were notably different from the present. This identified sensitivity in d as a source temperature proxy suggests that quantitative climate reconstructions from deuterium excess should be treated with caution for some sites when boundary conditions are significantly different from the present day. Also, the exclusion of the influence of humidity and other evaporative source changes in MCIM regressions may be a limitation of quantifying source temperature fluctuations from deuterium excess in some instances.