The stable isotope composition of hoarfrost

Atmospherically deposited hoarfrost is probably the least important quantitative component of the hydrosphere, yet in places acts as an important source of water. Although countless studies have investigated the stable isotope composition of virtually all other components of the global hydrosphere, little is known on its stable isotope composition. We addressed this gap in knowledge by investigating the stable isotope composition of hoarfrost and precipitation in the Southern Carpathian Mountains (East-Central Europe) in relation with the local and regional meteorological parameters and hoarfrost characteristics. Hoarfrost and precipitation were collected at the Țarcu Peak Weather Station (2180 m a.s.l.) between December 2018 and February 2019. The main sources of moisture (as indicated by high deuterium excess values) were the Black (and possibly Caspian) Sea as well as the terrestrial sources in Eastern Europe and Western Asia. Hoarfrost was deposited during periods of intense wind, with <i>δ</i>¹⁸O and <i>δ</i>²H being strongly correlated with air temperature. No correlation has been found between the intensity of hoarfrost deposition and its stable isotope characteristics. Our data indicates that the <i>δ</i>¹⁸O values of hoarfrost deposits faithfully record air temperature variability during deposition, while the <i>d</i>-excess parameter records conditions at the moisture sources.