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Acceleration of oxygen decline in the tropical Pacific over the past decades by aerosol pollutants

Abstract

Dissolved oxygen in the mid-depth tropical Pacific Ocean has declined in the past several decades1. The resulting expansion of the oxygen minimum zone has consequences for the region’s ecosystem2 and biogeochemical cycles3, but the causes of the oxygen decline are not yet fully understood. Here we combine models of atmospheric chemistry, ocean circulation and biogeochemical cycling to test the hypothesis that atmospheric pollution over the Pacific Ocean contributed to the redistribution of oxygen in deeper waters. We simulate the pollution-induced enhancement of atmospheric soluble iron and fixed nitrogen deposition, as well as its impacts on ocean productivity and biogeochemical cycling for the late twentieth century. The model reproduces the magnitude and large-scale pattern of the observed oxygen changes from the 1970s to the 1990s, and the sensitivity experiments reveal the reinforcing effects of pollution-enhanced iron deposition and natural climate variability. Despite the aerosol deposition being the largest in mid-latitudes, its effect on oceanic oxygen is most pronounced in the tropics, where ocean circulation transports added iron to the tropics, leading to an increased regional productivity, respiration and subsurface oxygen depletion. These results suggest that anthropogenic pollution can interact and amplify climate-driven impacts on ocean biogeochemistry, even in remote ocean biomes.

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Figure 1: Dissolved oxygen in the thermocline waters of the North Pacific.
Figure 2: Pollution-induced deposition of soluble iron and fixed nitrogen based on GEOS-Chem.
Figure 3: Simulated changes in the oxygen and sinking organic flux from the 1970s to the 1990s.
Figure 4: Breakdown of the simulated changes in the oxygen and sinking organic flux.

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References

  1. Stramma, L., Johnson, G. C., Sprintall, J. & Mohrholz, V. Expanding oxygen-minimum zones in the tropical oceans. Science 320, 655–658 (2008).

    Article  Google Scholar 

  2. Seibel, B. A. Critical oxygen levels and metabolic suppression in oceanic oxygen minimum zones. J. Exp. Biol. 214, 326–336 (2010).

    Article  Google Scholar 

  3. Codispoti, L. A. et al. The oceanic fixed nitrogen and nitrous oxide budgets: Moving targets as we enter the Anthropocene? Sci. Mar. 65, 85–105 (2001).

    Article  Google Scholar 

  4. Boyd, P. W. et al. Mesoscale iron enrichment experiments 1993–2005: synthesis and future directions. Science 315, 612–617 (2007).

    Article  Google Scholar 

  5. Garcia, H. E. et al. in Dissolved Oxygen, Apparent Oxygen Utilization, and Oxygen Saturation World Ocean Atlas 2009 Vol. 3 (ed. Levitus, S.) (U.S. Government Printing Office, 2010).

    Google Scholar 

  6. Vaquer-Sunyer, R. & Duarte, C. M. Thresholds of hypoxia for marine biodiversity. Proc. Natl Acad. Sci. USA 105, 15452–15457 (2008).

    Article  Google Scholar 

  7. Deutsch, C., Brix, H., Ito, T., Frenzel, H. & Thompson, L. Climate-forced variability of ocean hypoxia. Science 333, 336–339 (2011).

    Article  Google Scholar 

  8. Czeschel, R., Stramma, L. & Johnson, G. C. Oxygen decreases and variability in the eastern equatorial Pacific. J. Geophys. Res. 117, C11019 (2012).

    Article  Google Scholar 

  9. Stramma, L., Oschlies, A. & Schmidtko, S. Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr. Biogeosciences 9, 4045–4057 (2012).

    Article  Google Scholar 

  10. Deutsch, C. et al. Centennial changes in North Pacific anoxia linked to tropical trade winds. Science 345, 665–668 (2014).

    Article  Google Scholar 

  11. Tagliabue, A., Aumont, O. & Bopp, L. The impact of different external sources of iron on the global carbon cycle. Geophys. Res. Lett. 41, 920–926 (2014).

    Article  Google Scholar 

  12. Meskhidze, N., Chameides, W. L., Nenes, A. & Chen, G. Iron mobilization in mineral dust: can anthropogenic SO2 emissions affect ocean productivity? Geophys. Res. Lett. 30, 2085 (2003).

    Article  Google Scholar 

  13. Mahowald, N. M. et al. Atmospheric global dust cycle and iron inputs to the ocean. Glob. Biogeochem. Cycles 19, GB4025 (2005).

    Google Scholar 

  14. Meskhidze, N., Chameides, W. L. & Nenes, A. Dust and pollution: a recipe for enhanced ocean fertilization? J. Geophys. Res. 110, D03301 (2005).

    Google Scholar 

  15. Johnson, M. S. & Meskhidze, N. Atmospheric dissolved iron deposition to the global oceans: effects of oxalate-promoted Fe dissolution, photochemical redox cycling, and dust mineralogy. Geosci. Model Dev. 6, 1137–1155 (2013).

    Article  Google Scholar 

  16. Aumont, O., Bopp, L. & Schulz, M. What does temporal variability in aeolian dust deposition contribute to sea-surface iron and chlorophyll distributions? Geophys. Res. Lett. 35, L07607 (2008).

    Article  Google Scholar 

  17. Sholkovitz, E. R., Sedwick, P. N., Church, T. M., Baker, A. R. & Powell, C. F. Fractional solubility of aerosol iron: synthesis of a global-scale data set. Geochim. Cosmochim. Acta 89, 173–189 (2012).

    Article  Google Scholar 

  18. Duce, R. A. et al. Impacts of atmospheric anthropogenic nitrogen on the open ocean. Science 320, 893–897 (2008).

    Article  Google Scholar 

  19. Ito, T. & Deutsch, C. Variability of the oxygen minimum zone in the tropical North Pacific during the late twentieth century. Glob. Biogeochem. Cycles 27, 1119–1128 (2013).

    Article  Google Scholar 

  20. Boden, T. A., Marland, G. & Andres, R. J. Global, Regional, and National Fossil-Fuel CO2 Emissions (Oak Ridge National Laboratory U. S. Department of Energy, Carbon Dioxide Information Analysis Center, 2013).

    Google Scholar 

  21. Krishnamurthy, A. et al. Impacts of increasing anthropogenic soluble iron and nitrogen deposition on ocean biogeochemistry. Glob. Biogeochem. Cycles 23, GB3016 (2009).

    Article  Google Scholar 

  22. Krishnamurthy, A., Moore, J. K., Mahowald, N., Luo, C. & Zender, C. S. Impacts of atmospheric nutrient inputs on marine biogeochemistry. J. Geophys. Res. 115, G01006 (2010).

    Article  Google Scholar 

  23. Emerson, S., Watanabe, Y. W., Ono, T. & Mecking, S. Temporal trends in apparent oxygen utilization in the upper pycnocline of the North Pacific: 1980–2000. J. Oceanogr. 60, 139–147 (2004).

    Article  Google Scholar 

  24. Deutsch, C., Emerson, S. & Thompson, L. Physical-biological interactions in North Pacific oxygen variability. J. Geophys. Res. 111, C09S90 (2006).

    Article  Google Scholar 

  25. Boyd, P. W. & Tagliabue, A. Using the L concept to explore controls on the relationship between paired ligand and dissolved iron concentrations in the ocean. Mar. Chem. 173, 52–66 (2015).

    Article  Google Scholar 

  26. Weber, T. & Deutsch, C. Locan versus basin-scale of marine nitrogen fixation. Proc. Natl Acad. Sci. USA 111, 8741–8746 (2014).

    Article  Google Scholar 

  27. Myriokefalitakis, S. et al. Changes in dissolved Iron deposition to the oceans driven by human activity: a 3-D global modelling study. Biogeosciences 12, 3973–3992 (2015).

    Article  Google Scholar 

  28. Cabré, A., Marinov, I., Bernardello, R. & Bianchi, D. Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends. Biogeosciences 12, 5429–5454 (2015).

    Article  Google Scholar 

  29. Curry, R. & Nobre, C. Hydrobase3 (Woods Hole Oceanographic Institution, 2013).

    Google Scholar 

  30. Krishnamurthy, A., Moore, J. K., Zender, C. S. & Luo, C. Effects of atmospheric inorganic nitrogen deposition on ocean biogeochemistry. J. Geophys. Res. 112, G02019 (2007).

    Article  Google Scholar 

  31. Moore, J. K. & Braucher, O. Sedimentary and mineral dust sources of dissolved iron to the world ocean. Biogeosciences 5, 631–656 (2008).

    Article  Google Scholar 

  32. Conway, T. M. & John, S. G. The cycling of iron, zinc and cadmium in the north east Pacific Ocean – insights from stable isotopes. Geochim. Cosmochim. Acta 164, 262–283 (2015).

    Article  Google Scholar 

  33. Rue, E. L. & Bruland, K. W. Complexation of iron (III) by natural organic-ligands in the central North Pacific as determined by a new competitive ligand equilibration adsorptive cathodic stripping voltammetric method. Mar. Chem. 50, 117–138 (1995).

    Article  Google Scholar 

  34. Zhang, L. et al. Nitrogen deposition to the United States: distribution, sources, and processes. Atmos. Chem. Phys. 12, 4539–4554 (2012).

    Article  Google Scholar 

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Acknowledgements

T.I. is grateful for support from US National Science Foundation, grant number OCE-1242313. A.N. acknowledges support from the Cullen-Peck Faculty Fellowship and the Georgia Power Scholar Chair. J. Valett provided Supplementary Fig. 1. The authors would like to thank D. Jacob and the Harvard University Atmospheric Chemistry Modeling Group for providing the base GEOS-Chem model used during our research. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at NASA Ames Research Center.

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T.I. and A.N. initiated the research. T.I. was responsible for conducting ocean biogeochemistry simulations, analysis of the results and overall manuscript development. M.S.J. conducted atmospheric chemistry simulations. All authors contributed to the project planning, experimental design, the discussion of the results and their implications, as well as commenting on the manuscript.

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Correspondence to T. Ito.

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The authors declare no competing financial interests.

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Ito, T., Nenes, A., Johnson, M. et al. Acceleration of oxygen decline in the tropical Pacific over the past decades by aerosol pollutants. Nature Geosci 9, 443–447 (2016). https://doi.org/10.1038/ngeo2717

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