Lake carbonate-δ18O records from the Yukon Territory,Canada: Little Ice Age moisture variability and patterns |
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| Authors: | Lesleigh Anderson Bruce P Finney Mark D Shapley |
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| Institution: | 1. Centre for Limnology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, 61117 Rannu, Tartu County, Estonia;2. Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia;3. Estonian Marine Institute, University of Tartu, Mäealuse 14, 12618 Tallinn, Estonia;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742-4211, United States;3. Department of Geology, University of Maryland, College Park, MD 20742-4211, United States;4. CAS Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China;2. School of the Earth Science and Resources, China University of Geosciences, Beijing 100083, China;3. School of Engineering and Technology, China University of Geosciences, Beijing 100083, China;4. Institute of Oil Exploration and Development, Daqing Oilfield Company, Daqing 163712, China;5. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;6. Oil and Gas Survey, China Geological Survey, Beijing, 100029, China;1. Petrobras — Petroleo Brasileiro S.A., Avenida Chile, 330, Rio de Janeiro, RJ, Brazil;2. UNESP — Universidade Estadual Paulista, Instituto de Geociencias e Ciencias Exatas, Avenida 24A, 1515 Rio Claro, SP, Brazil |
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| Abstract: | A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ18O values decrease. Past lake-water δ18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ18O, supplemented by those in carbonate and organic δ13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ～AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ～AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ18O, a similarly small, stratified, alkaline lake located ～250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances. |
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