Holocene glacier history of Bjørnbreen and climatic reconstruction in central Jotunheimen,Norway, based on proximal glaciofluvial stream-bank mires |
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| Institution: | 1. Holocene Research Group, Department of Geography, University of Wales at Swansea, Singleton Park, Swansea SA2 8PP, UK;2. Department of Earth Science, University of Bergen, Allégaten 41, N-5007 Bergen, Norway, UK;3. Bjerknes Centre for Climatic Research, Allégaten 55, N-5007 Bergen, Norway, UK;4. Department of Geography, University of Bergen, Breiviken 2, N-5035 Bergen-Sandviken, Norway, UK;5. Department of Biology, University of Bergen, Allégaten 41, N-5007 Bergen, Norway, UK;6. Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1 H 0AP, UK;7. School of Geography, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK;8. School of Geography and Archaeology, University of Exeter, Exeter EX4 4RJ, UK;1. Department of Earth Science and Bjerknes Centre for Climate Research, University of Bergen, Norway;2. College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA;3. Department of Environmental Sciences, Western Norway University of Applied Sciences, Norway;1. Department of Biology, University of Bergen, P.O. Box 7803, Thormøhlens Gate 53 A, NO-5020 Bergen, Norway;2. Natural History Museum, University of Oslo, P.O. Box 1172, Blindern, NO-0318 Oslo, Norway;3. School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK;4. Department of Earth Science, University of Bergen, and Bjerknes Centre for Climate Research, P.O. Box 7803, NO-5020 Bergen, Norway;1. RWTH Aachen University, Department of Geography, Templergraben 55, 52062 Aachen, Germany;2. FAU Erlangen-Nürnberg, Department of Geography, Wetterkreuz 15, 91058 Erlangen, Germany;3. University of Cologne, Institute of Geography, Albertus-Magnus-Platz, 50923 Cologne, Germany;4. Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Lincui Road 16, 100101 Beijing, China;1. Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway;2. Uni Climate, Uni Research, Allégaten 55, 5007 Bergen, Norway;3. Bjerknes Centre for Climate Research, Allégaten 55, 5007 Bergen, Norway;4. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA;5. Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA;1. Department of Earth Science, University of Bergen and Bjerknes Centre for Climate Research, Postbox 7803, N-5020 Bergen, Norway;2. Department of Geology, University at Buffalo, Buffalo, NY 14260, USA;3. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA |
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| Abstract: | Holocene variations of Bjørnbreen, Smørstabbtinden massif, west-central Jotunheimen are reconstructed from the lithostratigraphy of two alpine stream-bank mires flooded episodically by meltwater. The approach uses multiple sedimentological indicators (weight loss-on-ignition, mean grain size, grain-size fractions, bulk density, moisture content and magnetic susceptibility), an a priori model of overbank deposition of suspended glaciofluvial sediments, a detailed chronology based on 56 radiocarbon dates, and a Little Ice Age sedimentological analogue. Rapid, late-Preboreal deglaciation was indicated by immigration of Betula pubescens by 9700 cal. BP. An interval of at least 3000 years in the early Holocene when glaciers were absent was interrupted by two abrupt episodes of glacier expansion around the time of the Finse Event, the first at ca 8270–7900 cal. BP (Bjørnbreen I Event) and the second at ca 7770–7540 cal. BP (Bjørnbreen II Event). Neoglaciation began shortly before ca 5730 cal. BP with gradual build-up to the maximum of the Bjørnbreen III Event at ca 4420 cal. BP. Later maxima occurred at ca 2750 cal. BP (Bjørnbreen IV Event) and at 1300, 1260, 1060 and 790 cal. BP (all within the Bjørnbreen V Event). Glaciers were smaller than today and possibly melted away on several occasions in the late Holocene (ca 3950, 1410 and 750 cal. BP). Minor maxima also occurred at ca 660 and 540 cal. BP, within the late Mediaeval Warm Period and the early Little Ice Age, respectively. The Little Ice Age maximum was dated to 213±25 BP (ca 205 cal. BP). The relative magnitudes of the main glacier maxima were determined: Erdalen Event>Little Ice Age Event (Bjørnbreen VI)>Bjørnbreen I (Finse Event) ≈ Bjørnbreen II>Bjørnbreen V?Bjørnbreen IV>Bjørnbreen III. These episodic events of varying magnitude and abruptness were used in conjunction with an independent summer-temperature proxy to reconstruct variations in equilibrium-line altitude (ELA) and a Holocene record of winter precipitation. Since the Preboreal, ELA varied within a range of about 390 m, and winter precipitation ranged between 40 and 160% of modern values. Winter precipitation variations appear to have been the main cause of these century- to millennial-scale Holocene glacier variations. |
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