Kinetic processes and stable isotopes in cave dripwaters as indicators of winter severity

Vasile Ersek,Aurel Perșoiu,Bogdan P Onac

doi:10.1002/hyp.13231

Abstract

AbstractWe examine how the stable isotope composition of meteoric water is transmitted through soil and epikarst to dripwaters in a cave in western Romania. δ2H and δ18O in precipitation at this site are influenced by temperature and moisture sources (Atlantic and Mediterranean), with lower δ18O in winter and higher in summer. The stable isotope composition of cave dripwaters mimics this seasonal pattern of low and high δ18O, but the onset and end of freezing conditions in the winter season are marked by sharp transitions in the isotopic signature of cave dripwaters of approximately 1 ‰. We interpret these shifts as the result of kinetic isotopic fractionation during the transition phase from water to ice at the onset of freezing conditions and the input of meltwater to the cave at the beginning of the spring season. This process is captured in dripwaters and therefore speleothems from Urșilor Cave, which grew under such dripping points, may have the potential to record past changes in the severity of winters. Similar isotopic changes in dripwaters driven by freeze–thaw processes can affect other caves in areas with winter snow cover, and cave monitoring during such changes is essential in linking the isotopic variability in dripwaters and speleothems to surface climate.

Highlights

| INTRODUCTIONThe stable isotopes of oxygen and hydrogen have been used for more than half of century to understand the hydrological cycle on regional and global scales (Dansgaard, 1964; Gat, 1981) as well as infer past climate changes by measuring their variability in ice cores (Oeschger et al, 1984; Thompson, Mosley‐Thompson, Dansgaard, & Grootes, 1986), speleothems (Bar‐Matthews, Ayalon, & Kaufman, 1997; Hendy & Wilson, 1968), ostracod shells (von Grafenstein, Erlenkeuser, Müller, Trimborn, & Alefs, 1996), or tree cellulose (McCarroll & Loader, 2004)
Knowledge of these would greatly improve our understanding of past climate changes, as well as the ability to forecast future ones, and we focus on isotopic changes in cave dripwaters that occur during the winter season
Mediterranean cyclones that reach western Romania are generally characterized by higher δ18O values in precipitation

Summary

| INTRODUCTION

The stable isotopes of oxygen and hydrogen have been used for more than half of century to understand the hydrological cycle on regional and global scales (Dansgaard, 1964; Gat, 1981) as well as infer past climate changes by measuring their variability in ice cores (Oeschger et al, 1984; Thompson, Mosley‐Thompson, Dansgaard, & Grootes, 1986), speleothems (Bar‐Matthews, Ayalon, & Kaufman, 1997; Hendy & Wilson, 1968), ostracod shells (von Grafenstein, Erlenkeuser, Müller, Trimborn, & Alefs, 1996), or tree cellulose (McCarroll & Loader, 2004). Insofar as the transfer of this climate signal through the vadose zone, it is necessary to monitor the changes in the stable isotopic signature of both rain and cave waters through time, together with changes in dripwater hydrology (Harmon, 1979). Studies investigating these variables have focused on the hydrological link between dripwaters and precipitation events. A sensitivity test with trajectories started 2 hours before or after the selected time indicated no significant differences in trajectory parameters

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| DISCUSSION

Findings

| CONCLUSIONS