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

Babette A. A. Hoogakker (), Zunli Lu (), Natalie Umling, Luke Jones, Xiaoli Zhou, Rosalind E. M. Rickaby, Robert Thunell, Olivier Cartapanis and Eric Galbraith
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Babette A. A. Hoogakker: Heriot-Watt University
Zunli Lu: Syracuse University
Natalie Umling: University of South Carolina
Luke Jones: University of Oxford
Xiaoli Zhou: Rutgers University
Rosalind E. M. Rickaby: University of Oxford
Robert Thunell: University of South Carolina
Olivier Cartapanis: University of Bern, Oeschger Centre for Climate Change Research
Eric Galbraith: Universitat Autonoma de Barcelona

Nature, 2018, vol. 562, issue 7727, 410-413

Abstract: Abstract 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 glacial1–3. 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.

Keywords: Eastern Tropical Pacific (ETP); Bottom Water Oxygen Concentration; Respiratory Carbon; Pacific Deep; Preformed Components (search for similar items in EconPapers)
Date: 2018
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DOI: 10.1038/s41586-018-0589-x

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