Stephen’s article, “Error estimates in the assessment of the isotopic composition of surface fluxes: A direct comparison of techniques using laser-based water vapor isotope analyzers” has just been accepted for publication in JGR-Atmospheres.
This article is derived from the analysis of a suite of observations and intercomparisons between eddy covariance, flux gradient, and Keeling-plot type methods for assessing the isotopic composition of evapotranspiration at landscape scales. After working through the sources of error inherent in each of the methods (while neglecting instrument error), Stephen is able to show that methods which depend on the covariance of water vapor concentration and isotopic composition directly (i.e. Keeling plot/mixing model approaches) perform better than eddy covariance approaches, which introduce additional uncertainty due to their inclusion of inherently low correlations between vertical wind and water vapor concentration. While we don’t think that this will be the last word on how to estimate landscape-scale isotopic composition of evapotranspiration using the current suite of closed-path optical spectroscopy, it’s nice to finally have some initial assessment of the quantitative uncertainty inherent in the varying strategies being used to tackle this issue.