Hydrologic changes in the Polar Ural Mountains between 24 and 1 ka using leaf wax hydrogen isotopes

Abstract:

We use hydrogen isotopes of mid- and long-chain n-alkanoic acids (δ²H_wax) in Lake Bolshoye Shchuchye, in the Polar Ural Mountains, to examine changes in precipitation seasonality and source from 1.3 to 23.5 ka, and compare with recently published pollen, DNA and geochemical datasets from the same sediments. Higher resolution sampling between 15 and 9 ka provides additional detail during late-glacial climate oscillations. Preliminary data suggest that the prominent feature of this record is a large transition to ²H-enriched values of all leaf wax chain lengths during the early Holocene, coinciding with the establishment of an aquatic plant community in Bolshoye Shchuchye, slightly higher overall primary productivity, and a northward expansion of the tree line. There were significant changes in terrestrial plant communities during the lateglacial as shown by pollen and DNA evidence, indicating temperature fluctuations prior to the Holocene. The lack of variability in δ²H_wax before 11 ka suggests that precipitation isotopes in the Polar Ural Mountains did not primarily reflect local temperatures, but instead were more sensitive to changes in moisture source and transport pathway. One possible mechanism influencing precipitation in this region is the Scandinavian Ice Sheet, which was a barrier to the westerlies until its demise in the Holocene, effectively attenuating changes in precipitation isotopes that occurred in Europe during this time period. Maximum lake evaporation and minimum snowfall occur between 10 and 7 ka, while moisture transport was probably most direct between 7 and 4 ka. These periods roughly coincide with the establishment of trees in Bolshoye Shchuchye’s catchment, supporting an inferred warm climate with milder winters. After 4 ka, δ²H_wax indicates a reduction in lake water evaporation or increased snowfall, both of which corroborate other evidence for cooler conditions after 4 ka, including the disappearance of trees from the catchment.