Letter

Net production of oxygen in the subtropical ocean

Received:
Accepted:
Published online:

Abstract

The question of whether the plankton communities in low-nutrient regions of the ocean, comprising 80% of the global ocean surface area, are net producers or consumers of oxygen and fixed carbon is a key uncertainty in the global carbon cycle1,2. Direct measurements in bottle experiments indicate net oxygen consumption in the sunlit zone3,4,5,6, whereas geochemical evidence suggests that the upper ocean is a net source of oxygen2. One possible resolution to this conflict is that primary production in the gyres is episodic1,2,6 and thus difficult to observe: in this model, oligotrophic regions would be net consumers of oxygen during most of the year, but strong, brief events with high primary production rates might produce enough fixed carbon and dissolved oxygen to yield net production as an average over the annual cycle. Here we examine the balance of oxygen production over three years at sites in the North and South Pacific subtropical gyres using the new technique of oxygen sensors deployed on profiling floats. We find that mixing events during early winter homogenize the upper water column and cause low oxygen concentrations. Oxygen then increases below the mixed layer at a nearly constant rate that is similar to independent measures of net community production. This continuous oxygen increase is consistent with an ecosystem that is a net producer of fixed carbon (net autotrophic) throughout the year, with episodic events not required to sustain positive oxygen production.

  • Subscribe to Nature for full access:

    $199

    Subscribe

Additional access options:

Already a subscriber?  Log in  now or  Register  for online access.

References

  1. 1.

    & Respiration in the open ocean. Nature 420, 379–384 (2002)

  2. 2.

    , , , , & Metabolic balance in the open sea. Nature 426, 32 (2003)

  3. 3.

    , & Respiration rates in bacteria exceed phytoplankton production in unproductive aquatic systems. Nature 385, 148–151 (1997)

  4. 4.

    & The CO2 balance of unproductive aquatic ecosystems. Science 281, 234–236 (1998)

  5. 5.

    , , & Regional carbon imbalances in the oceans. Science 284, 173–174 (1999)

  6. 6.

    , , & Net community production and metabolic balance at the oligotrophic ocean site, station ALOHA. Deep-Sea Res. I 51, 1563–1578 (2004)

  7. 7.

    , & Regional carbon imbalances in the oceans. Science 284, 173–174 (1999)

  8. 8.

    , , & Autonomous profiling floats: workhorse for broad-scale observations. Mar. Technol. Soc. J. 38, 21–29 (2004)

  9. 9.

    et al. in Observing the Oceans in the 21st Century (eds Koblinsky, K. & Smith, N.) 248–258 (Australian Bureau of Meteorology, Melbourne, Australia, 2001)

  10. 10.

    , , & The ocean takes a deep breath. Science 306, 1337 (2004)

  11. 11.

    , , & Chemical sensor networks for the aquatic environment. Chem. Rev. 107, 623–640 (2007)

  12. 12.

    & The Pacific shallow oxygen maximum, deep chlorophyll maximum, and primary productivity reconsidered. Deep-Sea Res. A 28, 901–919 (1981)

  13. 13.

    On the hydrogen and oxygen content of marine phytoplankton. Deep-Sea Res. I 42, 1675–1680 (1995)

  14. 14.

    , , & Role of late winter mesoscale events in the biogeochemical variability of the upper water column of the North Pacific Subtropical Gyre. J. Geophys. Res. 105, 28723–28739 (2000)

  15. 15.

    , & Seasonal and long-term dynamics of the upper ocean carbon cycle at Station ALOHA near Hawaii. Glob. Biogeochem. Cycles 18 doi: 10.1029/2004GB002227 (2004)

  16. 16.

    , , & Carbon-based ocean productivity and phytoplankton physiology from space. Glob. Biogeochem. Cycles 19 doi: 10.1029/2004GB002299 (2005)

  17. 17.

    , & Diatom fluxes to the deep sea in the oligotrophic North Pacific gyre at Station Aloha. Mar. Ecol. Prog. Ser. 182, 55–67 (1999)

  18. 18.

    , , & In situ determination of oxygen and nitrogen dynamics in the upper ocean. Deep-Sea Res. I 49, 941–952 (2002)

  19. 19.

    Ocean Data View 〈〉 (2006)

  20. 20.

    The solubility of nitrogen, oxygen and argon in water and seawater. Deep-Sea Res. A 17, 721–735 (1970)

Download references

Acknowledgements

We thank N. Larson for producing the oxygen sensors; D. Swift for his essential contributions to this effort; and the Hawaii Ocean Time-series participants for making dissolved oxygen data available. Research at the University of Washington was supported through the US Argo Program by the National Oceanographic and Atmospheric Administration and by the US Office of Naval Research through the National Ocean Partnership Program. Research at Monterey Bay Aquarium Research Institute was supported by a grant from the David and Lucile Packard Foundation and by the National Science Foundation.

Author Contributions S.C.R. originated the idea of putting oxygen sensors on profiling floats, and directed the construction and deployment of the floats as part of the international Argo project. K.S.J. performed the data analysis. Both authors contributed to the writing of the manuscript.

Author information

Affiliations

  1. School of Oceanography, University of Washington, Seattle, Washington 98195, USA

    • Stephen C. Riser
  2. Monterey Bay Aquarium Research Institute, Moss Landing, California 95039, USA

    • Kenneth S. Johnson

Authors

  1. Search for Stephen C. Riser in:

  2. Search for Kenneth S. Johnson in:

Corresponding authors

Correspondence to Stephen C. Riser or Kenneth S. Johnson.

All float data are available from the global Argo data center at ftp://usgodael.fnmoc.navy.mil/pub/outgoing/argo/.

Supplementary information

PDF files

  1. 1.

    Supplementary Figures

    The file contains Supplementary Figures 1-2 with Legends.