Conference Agenda

For decades, stable isotope applications in hydrology have concentrated on ²H, ¹⁸O, and their first-order derivative, the deuterium excess. Only recently has the least-abundant oxygen isotope, ¹⁷O, along with its relationship to ¹⁸O — the so-called ¹⁷O-excess (Δ′¹⁷O) — started to attract interest in the hydrological sciences. Applications encompass surface water hydrology, lake evaporation, and any geochemical exchange process involving water O isotope signatures and other matrices such as carbonates or silicates. Nevertheless, its broader application is hindered by the “emerging tracer dilemma,” which includes analytical and metrological challenges, as well as the lack of a homogeneous precipitation baseline dataset to serve as an input function for the hydrological cycle.

Drawing on the reanalysis of over 4,000 samples from the GNIP archive, we present fresh insights into the spatial and seasonal distribution of precipitation Δ′¹⁷O. This analysis incorporated Local Meteoric Water Lines from more than 80 locations worldwide, 22 of which are in Europe. The weighted regression slopes exhibited a broad range of distribution, although most were lower than that of the Global MWL. This establishes different starting metrics, such as those used in lake evaporation studies. Our research also included a six-year time series of daily sampled precipitation in Vienna, enabling us to correlate seasonal signatures of Δ′¹⁷O and deuterium excess with specific source regions.

The analysis of Δ′¹⁷O can provide an additional degree of freedom to hydrological studies, provided that the endmembers are sufficiently distinct relative to the analytical uncertainty. A systematic survey of surface waters, including lakes and wetlands, would enhance the understanding of ¹⁷O/¹⁸O patterns in evaporation-dominated settings. Strict quality control, such as the expansion of triple -isotope proficiency tests, will aid in benchmarking the precision and accuracy of the analytics, and assuring that data for hyrdological studies are fit for purpose.

New paleoclimate proxies like clumped isotope thermometry have reinvigorated the investigation of modern soil carbonate; these studies are of use to the paleoclimate proxy community as well as those who study modern soils. To date, most clumped isotope thermometry studies (T(∆₄₇)) of modern soil carbonates have been on carbonates from coarse-grained soils, and show a warm season bias of carbonate formation. Most of these studies have also assumed that soil water d18O, which can be calculated by combining T(∆₄₇) and pedogenic carbonate δ¹⁸O, shares the same seasonal bias as carbonate formation, but few have independently measured soil water δ¹⁸O with which to compare to these estimates. We applied clumped isotope thermometry to three fine-grained, clay-rich modern soils in Colorado and Nebraska, USA. At two sites, T(∆₄₇) overlaps with fall soil temperatures and the timing of soil dry down, suggesting carbonate forms during the fall. At the third site, mean T(∆₄₇) matches summer soil temperatures. Using a new soil water sampling device we built for this study, we independently measured soil water δ¹⁸O, which matched well with the calculated soil water δ¹⁸O for the two sites with cooler temperatures, while the calculated soil water δ¹⁸O at the third site had a significantly higher isotope value than any observations of soil water δ¹⁸O at that site. At all three sites, even in the fall season, measured soil water isotope values at carbonate bearing depths overlap with spring rainfall/snowmelt δ¹⁸O, with little to no evaporative enrichment of δ²H and δ¹⁸O values. These results show that (1) grain size is an important control on the timing of carbonate formation and soil water dynamics, (2) that the seasonal bias of soil water δ¹⁸O can differ from that of carbonate formation, and that (3) soil water δ¹⁸O at carbonate-bearing depths is relatively unaffected by evaporative enrichment.

Water vapor transport plays a pivotal role in snowpack metamorphism. This study presents multi-level measurements of isotopic compositions (δ¹⁸O, δ²H, d-excess) of water vapor within the snowpack pore space and ambient air. By integrating these measurements with comprehensive meteorological data and periodic isotope profiles, we explore the complex dynamics of water vapor within the snowpack-atmosphere continuum. Our findings reveal a depth and time-dependent disequilibrium between the ice matrix and water vapor in the snowpack pore space. Notably, there is a significant isotopic disequilibrium at the base of the snowpack near the ground, contrasting with near isotopic equilibrium in the upper layer. A warming event triggers a widespread transition toward isotopic disequilibrium throughout the snowpack. We hypothesize that ground vapor, initially confined to lower layers in a stratified state—maintained by a snowpack temperature gradient and supported by stable, saturated atmospheric conditions—spreads throughout the snowpack under near-isothermal conditions. This redistribution is influenced by a mixture of factors including solar radiation, temperature, turbulence, and the saturation potential of the atmosphere, which, together with surface sublimation fluxes, drives the water vapor from the snowpack pore space into the atmosphere. These observations underscore the necessity of incorporating non-equilibrium processes into isotope-enabled snowpack and climate models. This research provides essential insights into how dynamic environmental conditions, such as temperature fluctuations and phase transitions, rapidly influence isotopic variability in the snow-atmosphere continuum, offering significant implications for understanding and modelling water vapor transport in snowpacks.

In 2024, stable isotope samples (δ²H, δ¹⁸O) from ≈75 post-mining lakes, rivers, streams and ≈400 groundwater observations wells have been collected in the Lusatian lignite mining district, as an add-on to the long-term hydrological monitoring program of the mining administration company. The aim was to investigate, whether stable isotopes can be used as an additional tool to improve the understanding of groundwater- lake water interactions and to quantify evaporative loss from post-mining lakes. Samples from the post mining lakes were collected from different depths, and from different parts of the lakes, as well as in different seasons. Groundwater samples were collected from dump aquifers as well as from the surrounding natural aquifers. First results show that different parts of the Lusatian mining district can be discerned isotopically. While lake samples from the western (and northwestern part of the mining district show strongly negative deuterium excess (DE) values (up to -23), indicating higher evaporation loss, the DE values of groundwater samples of surrounding observation wells are consistently positive (with very few exceptions). In contrast, many groundwater samples from the southern part of the Lusatian mining district show comparably lower DE values, indicating lake water seepage into the groundwater. Further statistical analyses of the dataset will help to choose 3-4 representative lakes for in-depth studies, including a more thorough sampling program to study water balance and hydro-meteorological processes in more detail.