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  • 1. Cooper, Claire L.
    et al.
    Swindles, Graeme T.
    Watson, Elizabeth J.
    Savov, Ivan P.
    Gałka, Mariusz
    Gallego-Sala, Angela
    Borken, Werner
    Evaluating tephrochronology in the permafrost peatlands of northern Sweden2019In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 50, p. 16-28Article in journal (Refereed)
    Abstract [en]

    Tephrochronology is an increasingly important tool for the dating of sediment and peat profiles for palaeoecological, palaeoclimatic and archaeological research. However, although much work has been done on tephra in temperate peatlands, there have been very few in-depth investigations of permafrost peatlands. Here we present the analysis of nine peatland cores from Abisko, northern Sweden, and show that the presence of tephra layers may be highly variable even over a scale of <10 km. Using electron probe microanalysis (EPMA) combined with age-depth profiles compiled from radiocarbon (14C) and 210Pb dating of peat records, we identify the Hekla 1104, Hekla 1158, Hekla-Selsund and the Hekla 4 tephra layers. We also infer the presence of the Askja 1875 tephra, in addition to an unassigned tephra dating from between 1971–1987 AD in two separate cores. Five of the nine analysed cores do not contain distinct tephra layers. Volcanic ash deposits in northern Scandinavia are subject to both regional-scale variations in climate and atmospheric circulation, and local-scale variations on the order of tens of kilometres in topography, vegetation, snow cover, and ground permeability. The extreme inconsistency of tephra preservation within a small study area (∼3000 km2) brings into question the reliability of tephrochronology within permafrost peatlands, and highlights the necessity of alternative methods for dating peat profiles in this region.

  • 2.
    Kaufman, Darrell S.
    et al.
    No Arizona Univ, Sch Earth Sci & Environm Sustainabil, Flagstaff, AZ 86011 USA..
    Cooper, Katherine
    No Arizona Univ, Sch Earth Sci & Environm Sustainabil, Flagstaff, AZ 86011 USA..
    Behl, Richard
    Calif State Univ Long Beach, Dept Geol Sci, Long Beach, CA 90840 USA..
    Billups, Katharina
    Univ Delaware, Sch Marine Sci & Policy, Lewes, DE 19958 USA..
    Bright, Jordon
    Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA..
    Gardner, Karleen
    No Arizona Univ, Sch Earth Sci & Environm Sustainabil, Flagstaff, AZ 86011 USA..
    Hearty, Paul
    Univ N Carolina, Dept Environm Studies, Wilmington, NC 28403 USA..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Mendes, Isabel
    Univ Algarve, CIMA, P-8005139 Faro, Portugal..
    O'Leary, Michael
    Curtin Univ, Dept Environm & Agr, Bentley, WA 6102, Australia..
    Polyak, Leonid
    Ohio State Univ, Byrd Polar Res Ctr, Columbus, OH 43210 USA..
    Rasmussen, Tine
    Univ Tromso, Dept Geol, Tromso, Norway..
    Rosa, Francisca
    Univ Algarve, CIMA, P-8005139 Faro, Portugal..
    Schmidt, Matthew
    No Arizona Univ, Sch Earth Sci & Environm Sustainabil, Flagstaff, AZ 86011 USA..
    Amino acid racemization in mono-specific foraminifera from Quaternary deep-sea sediments2013In: Quaternary Geochronology, ISSN 1871-1014, E-ISSN 1878-0350, Vol. 16, p. 50-61Article in journal (Refereed)
    Abstract [en]

    The deep-sea environment is among the most stable on Earth, making it well suited for amino acid geochronology. Foraminifera with calcareous tests are distributed across the World Ocean and are often recovered in sufficient abundance from sediment cores to derive robust mean amino acid D/L values of multiple replicates from each stratigraphic level. The extent of racemization (D/L) can be compared with independent age control, which in most cases is based on correlation with global marine oxygen-isotope stages and radiocarbon ages from the same stratigraphic levels. In this study, we report the results of amino acid racemization analysis of multiple foraminifera species from well-dated sediment cores taken from the Pacific, Atlantic, and Arctic oceans. The composite of results analyzed to date (179 samples, each composed of an average of 8.6 subsamples = 1531 analyses) show that D/L values generally increase systematically down core, and are similar for samples of comparable ages from different deep-sea sites. Previously published equations that relate D/L values of aspartic and glutamic acids to post-depositional temperature and sample age for Pulleniatina obliquiloculata generally conform to the D/L trends for species analyzed in this study. Laboratory heating experiments were used to quantify the difference in the rate of racemization between P. obliquiloculata and other taxa. For example, aspartic acid in P. obliquiloculata racemizes an average of 12-16% faster than in the common high-latitude species, Neogloboquadrina pachyderma (s). Apparently, the unexpectedly high D/L values previously reported for N. pachyderma (s) older than 35 lea from the Arctic Ocean cannot be attributed to taxonomic effects. (C) 2012 Elsevier B.V. All rights reserved.

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