Holocene Climate Evolution of Continental Western Eurasia Constrained By Stable-Isotope and Cation Geochemistry of U-Th-Dated Speleothems and Meteogenic Travertine

• Main Author: Baker, Jonathan Lloyd
• Format: Thesis
• Language: unknown
• Published: University of Nevada, Las Vegas 2018
• Subjects: north atlantic current; North Atlantic; permafrost
• Online Access: https://dx.doi.org/10.34917/13568369; https://digitalscholarship.unlv.edu/thesesdissertations/3212

Reliable reconstructions of global and regional climate during the Holocene (11,700 years ago to present) are vital to constraining the natural range of climate variability and testing state-of-the-art models, which seek to forecast the near- and long-term impact of anthropogenic greenhouse forcing. Much of continental Eurasia is still underrepresented, however, in geological proxy reconstructions of Holocene climate variability, and the vast majority of paleoclimate data only reflect conditions during peak summer months (JJA) or the growing season. The paucity of winter proxy data has therefore been cited as a possible explanation for the current mismatch between geological proxy-based and climate-model reconstructions of Holocene temperature, but testing the hypothesis first requires additional datasets. In this series of studies, I seek to strengthen our knowledge of Holocene climate evolution in continental western Eurasia and mitigate the seasonal bias in paleoclimate proxy datasets by investigating two sites of freshwater carbonate deposition in western Russia: 1) Kinderlinskaya Cave, located in the southern Ural Mountains, and 2) the Izhora Plateau, south of the Gulf of Finland. Two speleothems collected from Kinderlinskaya Cave, which grew over the entire Holocene epoch, were analyzed for stable isotopes of oxygen and carbon. Carbon-isotope data constrain the timing of permafrost degradation and afforestation for the southern Ural Mountains, and the stable-isotope composition of oxygen in speleothem calcite is shown to reflect Holocene temperature evolution during the winter season. Centennial-scale trends in oxygen-isotope data are further utilized to establish a climate dynamic relationship between winter air temperature over western Russia and perturbations to the North Atlantic Current system over the last 11,700 years, providing a foundation from which to evaluate the regional climate response to feedbacks associated with anthropogenic warming. EarlyÐMiddle Holocene deposits of meteogenic (cool-water) travertine were also analyzed for stable isotopes of oxygen and carbon, as well as their major-cation concentrations (Mg and Sr). The oxygen-isotope composition of travertine deposits is shown to reflect winter climate variability in the Peribaltic region, for which our dataset constitutes the first winter paleoclimate archive, whereas the remaining geochemical proxies document changes to the surface hydrology and environment of the Izhora Plateau from approximately 9,500 to 6,800 years ago. From the results of these studies, we conclude that the winter and summer climate evolution of western continental Eurasia followed opposing trajectories for much of the Holocene. We further corroborate the hypothesis that geological proxy reconstructions of Holocene surface temperature are likely biased toward conditions during the summer half year by presenting data that strongly support the veracity of existing climate model reconstructions.