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Glacial expansion of oxygen-depleted seawater in the eastern tropical Pacific

Naturevolume 562pages410413 (2018) | Download Citation


Increased storage of carbon in the oceans has been proposed as a mechanism to explain lower concentrations of atmospheric carbon dioxide during ice ages; however, unequivocal signatures of this storage have not been found1. In seawater, the dissolved gases oxygen and carbon dioxide are linked via the production and decay of organic material, with reconstructions of low oxygen concentrations in the past indicating an increase in biologically mediated carbon storage. Marine sediment proxy records have suggested that oxygen concentrations in the deep ocean were indeed lower during the last ice age, but that near-surface and intermediate waters of the Pacific Ocean—a large fraction of which are poorly oxygenated at present—were generally better oxygenated during the glacial1,2,3. This vertical opposition could suggest a minimal net basin-integrated change in carbon storage. Here we apply a dual-proxy approach, incorporating qualitative upper-water-column and quantitative bottom-water oxygen reconstructions4,5, to constrain changes in the vertical extent of low-oxygen waters in the eastern tropical Pacific since the last ice age. Our tandem proxy reconstructions provide evidence of a downward expansion of oxygen depletion in the eastern Pacific during the last glacial, with no indication of greater oxygenation in the upper reaches of the water column. We extrapolate our quantitative deep-water oxygen reconstructions to show that the respired carbon reservoir of the glacial Pacific was substantially increased, establishing it as an important component of the coupled mechanism that led to low levels of atmospheric carbon dioxide during the glacial.

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Data availability

Data generated during this study are available from https://doi.pangaea.de/10.1594/PANGAEA.891185.

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This study benefited from discussions with R. Ganeshram. This work is supported by UK Natural Environment Research Council (NERC) grant NE/I020563/1 (to B.A.A.H.), National Science Foundation (NSF) grants OCE-1232620 and OCE-1736542 (to Z.L.) and Swiss National fund PP00P2_144811 (to O.C.). 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 the management of Joint Oceanographic Institutions (JOI), Inc. M. Hall, J. Rolfe and C. Day are acknowledged for help with stable isotope analyses.

Author information

Author notes

  1. Deceased: Robert Thunell


  1. The Lyell Centre, Heriot-Watt University, Edinburgh, UK

    • Babette A. A. Hoogakker
  2. Department of Earth Sciences, University of Oxford, Oxford, UK

    • Babette A. A. Hoogakker
    • , Luke Jones
    •  & Rosalind E. M. Rickaby
  3. Department of Earth Sciences, Syracuse University, Syracuse, NY, USA

    • Zunli Lu
  4. State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China

    • Zunli Lu
  5. School of Earth, Ocean and Environment, University of South Carolina, Columbia, SC, USA

    • Natalie Umling
    •  & Robert Thunell
  6. Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA

    • Xiaoli Zhou
  7. University of Bern, Oeschger Centre for Climate Change Research, Bern, Switzerland

    • Olivier Cartapanis
  8. Institut de Ciencia i Tecnologia Ambientals (ICTA) and Department of Mathematics, Universitat Autonoma de Barcelona, Bellaterra, Spain

    • Eric Galbraith
  9. ICREA, Barcelona, Spain

    • Eric Galbraith


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B.A.A.H. and Z.L. conceived and coordinated the work. B.A.A.H., Z.L., N.U., L.J. and X.Z. carried out data analyses; O.C. carried out data synthesis. B.A.A.H., Z.L. and E.G. constructed the figures and wrote the paper, with contributions from the other co-authors.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Babette A. A. Hoogakker or Zunli Lu.

Extended data figures and tables

  1. Extended Data Fig. 1 Details of age models for ODP sites 1242 and 849.

    a, Matching the ODP site 1242 benthic composite δ18O record to the Pacific Intermediate water stacked δ18O record of ref. 29. b, Matching the ODP site 849 benthic composite δ18O record to the Pacific deep water stacked δ18O record of ref. 29.

  2. Extended Data Fig. 2 Regional bulk sedimentary δ15N records.

    Dark green, bulk sedimentary δ15N record of ODP site 124249; light green, bulk sedimentary δ15N record of TR163-25 (this work); black, bulk sedimentary δ15N record of ODP site 84950.

  3. Extended Data Fig. 3 Overview and LGM evolution of carbon isotopes and oxygen concentrations in the eastern tropical Pacific.

    a, Dissolved oxygen concentrations (modern: North Atlantic north of 50° N, dark blue; South Atlantic south of 50° S, light blue; southeast Pacific south of 50° S, black; southwest Pacific south of 50° S, grey; northeast Pacific north of 50° N, dark purple; northwest Pacific north of 50° N, light purple; and reconstructed for the past 40 kyr: ODP site 1242, dark green; TR163-25, light green) plotted against carbon isotopes of DIC of seawater (‰) (data from refs 28,51 using https://www.nodc.noaa.gov/OC5/SELECT/dbsearch/dbsearch.html. Square boxes represent modern values at the two sites; diamonds represent LGM values (average 18–22 kyr bp). b, Latitudinal profile of the difference in Pacific carbon isotopes between the LGM (18–22 kyr, from epifaunal benthic foraminifera) and recent (DIC) seawater carbon isotopes (extrapolated from ref. 34). Inset, histogram of LGM-DIC δ13C (waters deeper than 1.3 km) has a normal distribution (0.1‰ bin width).

  4. Extended Data Table 1 Age control points for ODP sites 1242 and 849
  5. Extended Data Table 2 Age control points for TR163-25

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