Tephra in deglacial ocean sediments south of Iceland: Stratigraphy, geochemistry and oceanic reservoir ages

Authors

  • David J. R. Thornalley,

    Corresponding author
    1. The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
    Current affiliation:
    1. School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK.
    • at present address below.
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  • I. Nick McCave,

    1. The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
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  • Harry Elderfield

    1. The Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
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Abstract

Icelandic tephra layers within deglacial ocean sediment cores from south of Iceland have been detected and their timing with respect to the climate shifts of the last deglaciation constrained. Geochemical analysis of the tephra allowed the likely source volcanic systems to be identified. The previously known Saksunarvatn ash and Vedde ash are recognised and described. Several other major tephra layers are examined: basaltic eruption(s) of Katla at ∼8.4 ka; a basaltic eruption of Katla at ∼12.6 ka; a rhyolitic eruption of Katla at ∼13.6 ka producing tephra similar in appearance and composition to the Vedde ash; a basaltic eruption of Katla at ∼14.0 ka; and two basaltic eruptions of Grímsvötn at ∼14.6 ka and ∼15.0 ka. Abundant rhyolitic ash with a similar appearance and chemistry to the Vedde ash is found throughout the deglacial interval, predating the Vedde ash by up to 3000 years, supporting previous suggestions that there were pre-Vedde ash eruptions of rhyolite that may have contributed to North Atlantic Ash Zone 1.

This study expands the tephro-stratigraphic framework of the North Atlantic and provides a marine archive in which the timing of tephra layers (useful as isochrons) can be directly compared to major ocean and climate events of the last deglaciation. Furthermore, by correlating tephra layers and abundance changes in the polar foraminifera, Neogloboquadrina pachyderma (sinistral), to equivalent tephra events and inferred abrupt cooling/warming in Greenland ice-cores, contemporaneous 14C-dated planktonic foraminifera have been used to estimate changes in the surface radiocarbon reservoir age south of Iceland. Consistent with previous studies, larger surface reservoir ages are calculated during late Heinrich Stadial 1 and the Younger Dryas (∼2000 years and ∼800–1900 years respectively). Copyright © 2011 John Wiley & Sons, Ltd.

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