A 3000-year varved record of glacier activity and climate change from the proglacial lake Hvítárvatn,Iceland |
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| Authors: | Darren J Larsen Gifford H Miller Áslaug Geirsdóttir Thorvaldur Thordarson |
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| Institution: | 1. INSTAAR, Department of Geological Sciences, University of Colorado, UCB 450, Boulder, CO 80309, USA;2. Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík 101, Iceland;3. Earth and Planetary Science Group, School of Geosciences, University of Edinburgh, Grant Institute, The Kings Buildings, West Main Rd., Edinburgh EH9 3JW, United Kingdom;1. Antarctic Research Centre, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand;2. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand;3. Geochemistry, Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA;4. GNS Science, 1 Fairway Drive, Avalon 5010, PO Box 30-368, Lower Hutt 5040, New Zealand;5. GNS Science, 764 Cumberland Street, Dunedin 9016, New Zealand;6. Department of Earth Sciences and Climate Change Institute, University of Maine, Orono, ME 04469, USA;7. 20 Muir Road, Lake Hawea, RD2 Wanaka 9382, New Zealand;1. Department of Earth and Atmospheric Sciences & GEOTOP Research Center, University of Quebec at Montreal, Montreal, Quebec, Canada;2. Geological Survey of Canada, Ottawa, Ontario, Canada;1. Antarctic Research Centre, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand;2. School of Geography Environment and Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand;3. Lamont-Doherty Earth Observatory of Columbia University P.O. Box 1000, Palisades, NY 10964, USA;4. GNS Science, P.O. Box 30-368, Lower Hutt 5040, New Zealand;1. Oeschger Centre for Climate Change Research & Institute of Geography, University of Bern, Falkenplatz 16, 3012 Bern, Switzerland;2. Renard Centre of Marine Geology, Department of Geology and Soil Science, Ghent University, Krijgslaan 281 s.8, 9000 Gent, Belgium;3. Centro de Ciencias Ambientales EULA-Chile, Universidad de Concepción, Casilla 160-C, Concepción, Chile;1. School of Geography, University of Leeds, Woodhouse Lane, Leeds, West Yorkshire LS2 9JT, UK;2. Geography, Staffordshire University, Leek Road, Stoke-on-Trent, Staffordshire ST4 2DF, UK |
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| Abstract: | A suite of environmental proxies in annually laminated sediments from Hvítárvatn, a proglacial lake in the central highlands of Iceland, are used to reconstruct regional climate variability and glacial activity for the past 3000 years. Sedimentological analysis is supported by tephrostratigraphy to confirm the continuous, annual nature of the laminae, and a master varve chronology places proxies from multiple lake cores in a secure geochronology. Varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent Langjökull ice cap. The continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record. Varve thickness, varve thickness variance, ice-rafted debris, total organic carbon (mass flux and bulk concentration), and C:N of sedimentary organic matter, reveal a dynamic late Holocene climate with abrupt and large-scale changes in ice-cap size and landscape stability. A first-order trend toward cooler summers and ice-cap expansion is punctuated by notable periods of rapid ice cap growth and/or landscape instability at ca 1000 BC, 600 BC, 550 AD and 1250 AD. The largest perturbation began ca 1250 AD, signaling the onset of the Little Ice Age and the termination of three centuries of relative warmth during Medieval times. Consistent deposition of ice-rafted debris in Hvítárvatn is restricted to the last 250 years, demonstrating that Langjökull only advanced into Hvítárvatn during the coldest centuries of the Little Ice Age, beginning in the mid eighteenth century. This advance represents the glacial maximum for at least the last 3 ka, and likely since regional deglaciation 10 ka. The multi-centennial response of biological proxies to the Hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments, and catchment sensitivity to perturbations. |
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