Stable isotopes variation of long-chain diols in Lake Geneva

Rising global temperatures as a consequence of anthropogenic activities will have a profound effect on the hydrological cycle, with stark regional differences in its expression expected (IPCC report, 2014). However, changes in precipitation, seasonality, drought, storm intensification are difficult to predict despite their importance for societies. To improve predictions, a better mechanistic understanding of the regional response of the hydrological cycle to global changes is needed, which can be achieved by reconstructing changes in the hydrological cycle during the past using proxy records from geological archives.

The stable isotopic composition of environmental water (i.e. δ²H value) is an important tracer of the hydrological cycle. In the last decades lipid biomarker δ²H compositions have become particularly effective tools in lacustrine and marine archives to reconstruct paleohydrologcial changes throughout Earth history. This is because δ²H values of environmental water are recorded in the δ²H values of lipids from photosynthesizing organisms (e.g. Sachse et al., 2012). These lipids can be extracted to reconstruct past environmental water δ²H values in order to decipher the changes in the various compartments of the water cycle. Long-chain diols are biomolecules commonly found in sedimentary archives from marine and freshwater environments and are thought to be produced by eustigmatophytes (phototrophic microorganisms, Volkman et al., 1992). Freshwater long-chain diols are characterized by a high fractional abundance of the C₃₂ 1,15-diol (Lattaud et al., 2017) and are produced in situ in lakes and shallow ponds by eustigmatophyte algae, they will be transported to the sedimentary records with little degradation.

With the access to lacustrine δ²H from long-chain diols, we could access the δ²H of averaged continental precipitation within the catchment, understanding changes in evaporation within the lake and the tributaries influences as well as abrupt changes in the hydrological cycle.