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Glacial–interglacial changes in bottom-water oxygen content on the Portuguese margin

Nature Geoscience volume 8, pages 4043 (2015) | Download Citation


During the last and penultimate glacial maxima, atmospheric CO2 concentrations were lower than present, possibly in part because of increased storage of respired carbon in the deep oceans1. The amount of respired carbon present in a water mass can be calculated from its oxygen content through apparent oxygen utilization; the oxygen content can in turn be calculated from the carbon isotope gradient within the sediment column2. Here we analyse the shells of benthic foraminifera occurring at the sediment surface and the oxic/anoxic interface on the Portuguese Margin to reconstruct the carbon isotope gradient and hence bottom-water oxygenation over the past 150,000 years. We find that bottom-water oxygen concentrations were 45 and 65 μmol kg−1 lower than present during the last and penultimate glacial maxima, respectively. We calculate that concentrations of remineralized organic carbon were at least twice as high as today during the glacial maxima. We attribute these changes to decreased ventilation linked to a reorganization of ocean circulation3 and a strengthened global biological pump4. If the respired carbon pool was of a similar size throughout the entire glacial deep Atlantic basin, then this sink could account for 15 and 20 per cent of the glacial PCO2 drawdown during the last and penultimate glacial maxima.

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This work is supported by UK Natural Environment Research Council (NERC) grant NE/I020563/1 (to B.A.A.H.). This research used samples and/or data provided by the Ocean Drilling Program (ODP). ODP is sponsored by the US National Science Foundation and participating countries (Natural Environment Research Council in the UK) under management of the Joint Oceanographic Institutions (JOI).

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  1. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK

    • Babette A. A. Hoogakker
    •  & Rosalind E. M. Rickaby
  2. Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Downing Street Cambridge CB2 3EQ, UK

    • Henry Elderfield
    •  & I. Nick McCave
  3. Universität Hamburg, Centrum für Erdsystemforschung und Nachhaltigkeit, Institut für Geologie, Bundesstrasse 55 D-20146 Hamburg, Germany

    • Gerhard Schmiedl


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B.A.A.H. conceived and coordinated the work, carried out data analyses and synthesis, and constructed the figures. B.A.A.H. wrote the paper with contributions from the other co-authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Babette A. A. Hoogakker.

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