Lake Water Isotope Gradients in Arctic Norway, Sweden and Finland: Implications for Proxy-based Precipitation Reconstructions

Abstract:

Amplified warming is predicted to cause an intensification of the Arctic hydrological cycle. To improve our understanding of the dynamics controlling Arctic precipitation, we use proxy records of past precipitation seasonality. The hydrogen isotopic composition (δ²H) of sedimentary biomarkers is widely used to infer hydrological changes over long time scales, with recent dual biomarker approaches focusing on the comparison between waxes produced by aquatic and terrestrial plants to reconstruct seasonality and aridity. These approaches rely on the assumption that aquatic plant biomarker δ²H values are minimally impacted by evaporative enrichment. In order to make accurate paleoclimate interpretations, we need to improve our understanding of the processes influencing lake water isotopic composition, and quantify their relative importance.

We analyzed the water isotopic composition of 135 lakes in Arctic Norway, Sweden and Finland along a NW-SE transect from the Norwegian Sea to the Baltic Sea, as well as 33 lakes on Svalbard, an Arctic archipelago north of Norway. By comparing lakes with different characteristics (e.g., degree of connectivity to other lakes, elevation, and distance from the ocean), we investigate the influence of moisture transport and evaporative enrichment on the isotopic composition of lake water. To evaluate the interannual variability, 16 of the lakes have been sampled on the same dates for two or three consecutive years. Preliminary results suggest that the inland lakes have similar inflow values, but experience more evaporation farther away from the coast, with lake water isotope values falling along a local evaporation line. In contrast, lakes close to the ocean have water isotope values that fall along the meteoric water line. Their water isotopic compositions are more variable, which could be explained by more heterogeneous atmospheric and lake and catchment morphometric conditions resulting in variable inflow values. We use our observational data to identify modern controls on lake water isotopes, providing guidance for choosing lakes that can be used for dual biomarker approaches, and support for paleoclimate inferences.