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Diatom and stable isotope records of late-Holocene lake ontogeny at Indrepollen, Lofoten, NW Norway: a response to glacio-isostasy and Neoglacial cooling

Department of Geography, Loughborough University, Loughborough LE11 3TU, UK, k.mills{at}lboro.ac.uk

Anson W. Mackay

Environmental Change Research Centre, Department of Geography, Pearson Building, Gower Street, University College London, London WC1E 6BT, UK

Raymond S. Bradley

Department of Geosciences, University of Massachusetts, Amherst MA 01003, USA

Bruce Finney

Institute of Marine Science, University of Alaska Fairbanks, Fairbanks AK 99775-7220, USA, Department of Biological Sciences, Idaho State University, Pocatello ID 83209-8007, USA

Borg Indrepollen is a coastal lake on the island of Vestvågøy, Lofoten, NW Norway. A sedimentary sequence spanning the last 4500 cal. yr BP was analysed for diatom, C/N and stable isotopes (¹³C and ¹⁵ N). The record provides clear evidence of glacio-isostatic rebound in the Lofoten region. Five distinct lithostratigraphic-geochemical zones (I—V) and four major diatom zones (A—D) were identified. The early record (I—III, A—Biii; 4500—550 cal. yr BP) contains coarse sedimentary material and diatoms indicative of more marine conditions. The correlation between the isotopic data (high ¹³C and low C/N) and trends in the biological data (marine/brackish flora) suggest the marine influence on the Indrepollen basin is a controlling factor of the source of organic material. The latter part of the record (IV, C; 550 cal. yr 550—226) indicates a transitional phase from marine-dominated diatom to brackish taxa and is coincident with a section of microlaminations in the core. The youngest zone (V, D; 226 cal. yr BP—present) is indicative of an isolated basin, with the deposition of fine sediments; freshwater diatom taxa dominate the biological record and ¹³C are indicative of freshwater conditions. C/N suggests a shift to a terrestrial source of organic matter. The proxies show a transition from full marine conditions, when Indrepollen was a submerged fjord, to more freshwater, lacustrine conditions in the last 200 years. The record of land uplift from Borg Indrepollen mirrors changes in sedimentary records from across Northern Norway and relative sea-level curves for the region.

Key Words: Diatoms • stable isotopes • sea-level • lake ontogeny • land uplift • glacio-isostasy • palaeoconductivity • Lofoten • Norway • late Holocene.

The Holocene, Vol. 19, No. 2, 261-271 (2009)
DOI: 10.1177/0959683608100571


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