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Amazon River enhances diazotrophy and carbon sequestration in the tropical North Atlantic Ocean

  1. D. G. Capone‡‡
  1. *Lamont–Doherty Earth Observatory, Columbia University, Palisades, NY 10964;
  2. ‡Department of Marine Sciences, University of Georgia, Athens, GA 30602;
  3. §Romberg Tiburon Center, San Francisco State University, Tiburon, CA 94920;
  4. Department of Earth and Ocean Science, University of Liverpool, Liverpool L69 3GP, United Kingdom;
  5. ‖Department of Oceanography, SOEST, University of Hawaii, Honolulu, HI 96822;
  6. **Institute of Marine and Coastal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901;
  7. ††School of Biology, Georgia Institute of Technology, Atlanta, GA 30332;
  8. ‡‡Wrigley Institute for Environmental Studies and Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089; and
  9. §§Department of Ecology and Evolutionary Biology and Institute of the Environment, University of California, Los Angeles, CA 90095

  1. Edited by David M. Karl, University of Hawaii, Honolulu, HI, and approved April 24, 2008 (received for review October 29, 2007)

Abstract

The fresh water discharged by large rivers such as the Amazon is transported hundreds to thousands of kilometers away from the coast by surface plumes. The nutrients delivered by these river plumes contribute to enhanced primary production in the ocean, and the sinking flux of this new production results in carbon sequestration. Here, we report that the Amazon River plume supports N2 fixation far from the mouth and provides important pathways for sequestration of atmospheric CO2 in the western tropical North Atlantic (WTNA). We calculate that the sinking of carbon fixed by diazotrophs in the plume sequesters 1.7 Tmol of C annually, in addition to the sequestration of 0.6 Tmol of C yr−1 of the new production supported by NO3 delivered by the river. These processes revise our current understanding that the tropical North Atlantic is a source of 2.5 Tmol of C to the atmosphere [Mikaloff-Fletcher SE, et al. (2007) Inverse estimates of the oceanic sources and sinks of natural CO2 and the implied oceanic carbon transport. Global Biogeochem Cycles 21, doi:10.1029/2006GB002751]. The enhancement of N2 fixation and consequent C sequestration by tropical rivers appears to be a global phenomenon that is likely to be influenced by anthropogenic activity and climate change.

Footnotes

  • ↵†To whom correspondence should be addressed at: LDEO/Columbia University, 61 Route 9W, Palisades, NY 10964. E-mail: ajit{at}ldeo.columbia.edu

  • Author contributions: A.S., P.L.Y., E.J.C., S.A.S.-W., and D.G.C. designed research; A.S., P.L.Y., E.J.C., C.M., K.B., S.C., A.B.K., R.S., and D.G.C. performed research; A.S. and S.A.S.-W. contributed new reagents/analytic tools; A.S., P.L.Y., C.M., K.B., S.C., J.P.M., S.A.S.-W., R.S., and D.G.C. analyzed data; and A.S., P.L.Y., E.J.C., C.M., and D.G.C. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/cgi/content/full/0710279105/DCSupplemental.

  • Received October 29, 2007.

Freely available online through the PNAS open access option.

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