Drivers of precipitation stable oxygen isotope variability in an alpine setting, Snowy Mountains, Australia

摘要

Natural archives that preserve a stable isotopic signature are routinely used to reconstruct palaeoenvironmental conditions. Isotopic values of precipitation are known to be influenced by factors such as the amount and type of precipitation, moisture pathway, landscape and terrain factors, and processes associated with precipitation formation and deposition. This study investigates oxygen isotopic variability using real-time rain and snow precipitation data from a moderate altitude (<2250mabove sea level), Southern Hemisphere alpine environment, where the causes of isotopic variability are largely unknown. Previous research at Global Network of Isotopes in Precipitation sites skewed toward rain precipitation, low-altitude, predominantly coastal locations identified amount effects as the dominant explanation of isotopic variability in southern Australia. This study based onwithin- and between-event real-time sampling finds that the origin of moisture and terrain effects are the dominant cause of isotopic variability in this alpine region, with little evidence of amount effects. Rainfall that originated from similar Southern Ocean latitudes showed a consistent (moderate) isotopic signature (δ~(18)O -6.5 to -8‰). Depleted isotopic signatures are associated with prefrontal activity and intense circulation such as east coast lows. Localized thunderstorms have a more neutral isotopic signature. A windward to leeward depletion (-0.5‰δ~(18)O) and an elevation impact (-0.5‰δ~(18)O 100m~(-1)) were found also. These results have significant implications for understanding atmospheric drivers of isotopic variability from which oxygen isotope-based palaeoclimate reconstruction is informed in regions with complex topography and geographically diverse moisture pathways such as the Australian Alps.