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On the use of dissolved oxygen isotopologues as biogeochemical tracers in the Pacific Ocean
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  • Boda Li,
  • Huanting Hu,
  • William M. Berelson,
  • Jess Adkins,
  • Laurence Y Yeung
Boda Li
Rice University, Rice University
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Huanting Hu
Shanghai Jiaotong University, Shanghai Jiaotong University
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William M. Berelson
University of Southern California, University of Southern California
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Jess Adkins
California Institute of Technology, California Institute of Technology
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Laurence Y Yeung
Rice University, Rice University

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The isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by 18O/16O and 17O/16O ratios in dissolved oxygen. In particular, puzzlingly low 17O/16O ratios observed for some low-oxygen samples have been difficult to explain. To improve our understanding of oxygen cycling in the ocean’s interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2-D isotopologue-enabled isopycnal reaction-transport model. We measured 18O/16O and 17O/16O ratios, as well as the “clumped” 18O18O isotopologue in the northeast Pacific, and compared the results to previously published data. We find that transport and respiration rates constrained by O2 concentrations in the oligotrophic Pacific yield good measurement-model agreement across all O2 isotopologues only when using a recently reported set of respiratory isotopologue fractionation factors that differ from those most often used for oxygen cycling in the ocean. These fractionation factors imply that an elevated proportion of 17O compared to 18O in dissolved oxygen―i.e., its triple-oxygen isotope composition―does not uniquely reflect gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed.
Dec 2022Published in Journal of Geophysical Research: Oceans volume 127 issue 12. 10.1029/2022JC018617