Abstract
Abstract. The stable isotopic composition of water vapour provides information about moisture sources and processes difficult to obtain with traditional measurement techniques. Recently, it has been proposed that the D-excess of water vapour (dv = δ2H − 8 × δ18O) can provide a diagnostic tracer of continental moisture recycling. However, D-excess exhibits a diurnal cycle that has been observed across a variety of ecosystems and may be influenced by a range of processes beyond regional-scale moisture recycling, including local evaporation (ET) fluxes. There is a lack of measurements of D-excess in evaporation (ET) fluxes, which has made it difficult to assess how ET fluxes modify the D-excess in water vapour (dv). With this in mind, we employed a chamber-based approach to directly measure D-excess in ET (dET) fluxes. We show that ET fluxes imposed a negative forcing on the ambient vapour and could not explain the higher daytime dv values. The low dET observed here was sourced from a soil water pool that had undergone an extended drying period, leading to low D-excess in the soil moisture pool. A strong correlation between daytime dv and locally measured relative humidity was consistent with an oceanic moisture source, suggesting that remote hydrological processes were the major contributor to daytime dv variability. During the early evening, ET fluxes into a shallow nocturnal inversion layer caused a lowering of dv values near the surface. In addition, transient mixing of vapour with a higher D-excess from above the nocturnal inversion modified these values, causing large variability during the night. These results indicate d
Highlights
Climate change has the potential to significantly impact surface and atmospheric water budgets
To determine how local ET fluxes modified water vapour D-excess, in situ observations were collected in a semi-arid region of south-eastern Australia
With chamber-based measurements of isotopic compositions in evaporative fluxes, it was shown that local ET fluxes exhibited a negative forcing on the ambient water vapour D-excess that could not explain the high daytime values
Summary
Climate change has the potential to significantly impact surface and atmospheric water budgets. Our best understanding of future exchanges between the atmospheric water cycle and the land surface for regional to global scales is likely to be gained through analysis of numerical simulations (Decker et al, 2015; Evans and McCabe, 2010; Harding and Snyder, 2012; Wei et al, 2012). Continual improvement of available models is essential, but this is contingent upon ongoing validation and evaluation of model performance over a broad range of landscapes and climate types (McCabe et al, 2016). To do this effectively, a diversity of datasets that directly quantify processes represented within these models are required (McCabe et al, 2005). Datasets that directly measure land–atmosphere exchange at the process level are limited (Jana et al, 2016).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call