Pre-glacial and interglacial pollen records over the last 3 Ma from northwest Canada: Why do Holocene forests differ from those of previous interglaciations? |
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| Authors: | Charles Schweger Duane Froese James M White John A Westgate |
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| Institution: | 1. Department of Anthropology, University of Alberta, Edmonton, Alberta, Canada T6G 2H4;2. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E3;3. Natural Resources Canada, Geological Survey of Canada, Calgary, Alberta, Canada T2L 2A7;4. Department of Geology, University of Toronto, Toronto, Ontario, Canada M5S 3B1;1. Geosciences Department, Williams College, 947 Main Street, Williamstown, MA 01267, USA;2. Ocean Sciences Department, University of California, 1156 High Street, Santa Cruz, CA 95064, USA;3. College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA;4. e4 Sciences, 27 Glen Road, Sandy Hook, CT 06482, USA;5. School for Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA;1. Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, USA;2. Geography and Environment, University of Southampton, Highfield, Southampton SO17 1BJ, UK;3. Alaska Quaternary Center, University of Alaska-Fairbanks, Fairbanks, AK 99775, USA;4. Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA;5. Department of Biological Sciences, Idaho State University, Pocatello, ID 83209, USA;6. Department of Geosciences, Idaho State University, Pocatello, ID 83209, USA;1. Department of Earth Sciences and Swire Institute of Marine Science, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region;2. Centre for Coastal Biogeochemistry, School of the Environment, Science and Engineering, Southern Cross University, Australia;3. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research c/o GEOMAR, Helmholtz Centre for Ocean Research, Wischhofstrasse 1-3, 24148, Kiel, Germany;4. Institute of Marine Sciences, University of California, Santa Cruz, CA, 95064, USA;5. School of Life Sciences and Simon F.S. Li Marine Laboratory, The Chinese University of Hong Kong, Shatin, Hong Kong Special Administrative Region;1. Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA, USA;2. Department of Biological Sciences, Idaho State University, Pocatello, ID, USA;3. Department of Geosciences, Idaho State University, Pocatello, ID, USA;4. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA;1. Oregon State University, College of Earth, Ocean, and Atmospheric Sciences (CEOAS), Corvallis, OR, USA;2. University of Pittsburgh, Department of Geology and Planetary Science, Pittsburgh, PA, USA;3. Canada Research Chair in Marine Geology, Institut des sciences de la mer de Rimouski (ISMER) & GEOTOP, Rimouski, Québec, Canada |
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| Abstract: | We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea–Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness. |
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