Ocean nutrient ratios governed by plankton biogeography

Journal name:
Nature
Volume:
467,
Pages:
550–554
Date published:
DOI:
doi:10.1038/nature09403
Received
Accepted
Published online

Abstract

The major nutrients nitrate and phosphate have one of the strongest correlations in the sea, with a slope similar to the average nitrogen (N) to phosphorus (P) content of plankton biomass (N/P = 16:1). The processes through which this global relationship emerges despite the wide range of N/P ratios at the organism level are not known. Here we use an ocean circulation model and observed nutrient distributions to show that the N/P ratio of biological nutrient removal varies across latitude in Southern Ocean surface waters, from 12:1 in the polar ocean to 20:1 in the sub-Antarctic zone. These variations are governed by regional differences in the species composition of the plankton community. The covariation of dissolved nitrate and phosphate is maintained by ocean circulation, which mixes the shallow subsurface nutrients between distinct biogeographic provinces. Climate-driven shifts in these marine biomes may alter the mean N/P ratio and the associated carbon export by Southern Ocean ecosystems.

At a glance

Figures

  1. Observed N* distribution in the Southern Ocean.
    Figure 1: Observed N* distribution in the Southern Ocean.

    a, Zonal mean section of N* ([NO3]16[PO43−]), with potential density anomaly contours (ρθ1,000kgm−3; thin lines) and schematic large-scale meridional overturning circulation patterns (arrows). Upwelling circumpolar deep water (CDW) is driven across the Antarctic polar front (APF) and the sub-Antarctic front (SAF) by Ekman transport, and subsides in the polar frontal zone (PFZ) to form Antarctic intermediate water (AAIW) and sub-Antarctic mode water (SAMW). b, Zonal mean vertical difference in N* between the surface and the thermocline (ΔN* = N*0–75mN*200–800m), globally and in individual sectors of the Southern Ocean.

  2. Redfield N* prediction.
    Figure 2: Redfield N* prediction.

    Southern Ocean surface N* gradient (dashed line) and ΔN* (solid line) predicted in model 1, assuming nutrient uptake and remineralization at the Redfield ratio. The northward increase in surface N* and low ΔN* values are inconsistent with observations.

  3. Diagnosed nutrient export ratios.
    Figure 3: Diagnosed nutrient export ratios.

    a, Spatial pattern of N/Pexp, derived in model 2 by diagnosing the export of NO3 and PO43− independently. b, Zonal mean export ratio (solid line) and contribution of diatoms to N export (dashed line) diagnosed in model 2. The grey envelope is an estimate of errors associated with the choice of model compensation depth (50–100m), the biological damping timescale (14d to 1yr) and the parameterization of dissolved organic matter (see Supplementary Information).

  4. Circulation averaging of remineralized nutrients.
    Figure 4: Circulation averaging of remineralized nutrients.

    Depth profiles of [NO3]rem/[PO43−]rem in the Antarctic (solid line), Polar frontal (dotted line) and sub-Antarctic (dashed line) zones predicted in model 3. The reduction in variability with depth results from the physical mixing of remineralized nutrients.

References

  1. Redfield, A. C. The biological control of chemical factors in the environment. Am. Sci. 46, 205221 (1958)
  2. Sterner, R. W. & Elser, J. J. Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere 80–134 (Princeton Univ. Press, 2002)
  3. Falkowski, P. G. Rationalizing elemental ratios in unicellular algae. J. Phycol. 36, 36 (2000)
  4. Anderson, L. A. & Sarmiento, J. L. Redfield ratios of remineralization determined by nutrient data analysis. Glob. Biogeochem. Cycles 8, 6580 (1994)
  5. Takahashi, T., Broecker, W. S. & Langer, S. Redfield ratio based on chemical data from isopycnal surfaces. J. Geophys. Res. 90, 69076924 (1985)
  6. Codispoti, L. A. in Productivity of the Ocean: Past and Present (eds Berger, W. H., Smetacek, V. S. & Wefer, G.) 377394 (Wiley, 1989)
  7. Broecker, W. S. Glacial to interglacial changes in ocean chemistry. Prog. Oceanogr. 2, 151197 (1982)
  8. Tyrrell, T. The relative influences of nitrogen and phosphorus on oceanic primary production. Nature 400, 525531 (1999)
  9. Geider, R. J. & La Roche, J. Redfield revisited: variability of C:N:P in marine microalgae and its biochemical basis. Eur. J. Phycol. 37, 117 (2002)
  10. Quigg, A. et al. The evolutionary inheritance of elemental stoichiometry in marine phytoplankton. Nature 425, 291294 (2003)
  11. Finkel, Z. V. et al. Irradiance and the elemental stoichiometry of marine phytoplankton. Limnol. Oceanogr. 51, 26902701 (2006)
  12. Klausmeier, C. A., Litchman, E., Daufresne, T. & Levin, S. A. Optimal nitrogen-to-phosphorus stoichiometry of phytoplankton. Nature 429, 171174 (2004)
  13. Gruber, N. & Sarmiento, J. L. Global patterns of marine nitrogen fixation and denitrification. Glob. Biogeochem. Cycles 11, 235266 (1997)
  14. Karl, D. M. & Michaels, A. F. in Encyclopedia of Ocean Sciences Vol. 4 (eds Steele, J. H., Turekian, K. K. & Thorpe, S. A.) 18761884 (Academic, 2001)
  15. Dentener, F. et al. Nitrogen and sulfur deposition on regional and global scales: a multimodel evaluation. Glob. Biogeochem. Cycles 20, GB4003 (2006)
  16. Codispoti, L. A. & Christensen, J. P. Nitrification, denitrification, and nitrous oxide cycling in the eastern tropical Pacific Ocean. Mar. Chem. 16, 277300 (1985)
  17. Garcia, H. E., Locarni, R. A., Boyer, T. P. & Antonov, J. I. World Ocean Atlas 2005 Vol. 4 Nutrients (Phosphate, Nitrate, Silicate) (US Government Printing Office, 2006)
  18. Orsi, A. H., Whitworth, T. W. & Nowlin, W. D. On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep-Sea Res. I 42, 641673 (1995)
  19. Schlitzer, R. Carbon export fluxes in the Southern Ocean: results from inverse modeling and comparison with satellite-based estimates. Deep-Sea Res. II 49, 16231644 (2002)
  20. Green, S. E. & Sambrotto, R. N. Plankton community structure and export of C, N, P and Si in the Antarctic Circumpolar Current. Deep-Sea Res. II 53, 620643 (2006)
  21. Longhurst, A. Seasonal cycles of pelagic production and consumption. Prog. Oceanogr. 36, 77167 (1995)
  22. Kopczynska, E. E., Weber, L. H. & El-Sayed, S. Z. Phytoplankton species composition and abundance in the Indian sector of the Antarctic Ocean. Polar Biol. 6, 161169 (1986)
  23. Jin, X., Gruber, N., Dunne, J. P., Sarmiento, J. L. & Armstrong, R. A. Diagnosing the contribution of phytoplankton functional groups to the production and export of particulate organic carbon, CaCO3, and opal from global nutrient and alkalinity distributions. Glob. Biogeochem. Cycles 20, GB2015 (2006)
  24. Price, N. M. The elemental stoichiometry and composition of an iron-limited diatom. Limnol. Oceanogr. 50, 11591171 (2005)
  25. Fu, F. X., Warner, M. E., Zhang, Y. H., Feng, Y. Y. & Hutchins, D. A. Effects of increased temperature and CO2 on photosynthesis, growth, and elemental ratios in marine Synechococcus and Prochlorococcus (Cyanobacteria). J. Phycol. 43, 485496 (2007)
  26. Arrigo, K. R. et al. Phytoplankton community structure and the drawdown of nutrients and CO2 in the Southern Ocean. Science 283, 365367 (1999)
  27. Karl, D. et al. The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean. Nature 388, 533538 (1997)
  28. Wu, J. F., Sunda, W., Boyle, E. A. & Karl, D. M. Phosphate depletion in the western North Atlantic Ocean. Science 289, 759762 (2000)
  29. Anderson, R. F. et al. Wind-driven upwelling in the Southern Ocean and the deglacial rise in atmospheric CO2 . Science 323, 14431448 (2009)
  30. Elderfield, H. & Rickaby, R. E. M. Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean. Nature 405, 305310 (2000)
  31. Sarmiento, J. L. & Toggweiler, J. R. A new model for the role of the oceans in determining atmospheric PCO2 . Nature 308, 621624 (1984)
  32. Le Quere, C. et al. Saturation of the Southern Ocean CO2 sink due to recent climate change. Science 316, 17351738 (2007)
  33. Sarmiento, J. L. et al. Response of ocean ecosystems to climate warming. Glob. Biogeochem. Cycles 18, GB3003 (2004)
  34. Khatiwala, S., Visbeck, M. & Cane, M. A. Accelerated simulation of passive tracers in ocean circulation models. Ocean Model. 9, 5169 (2005)
  35. Brzezinski, M. A. et al. A switch from Si(OH)4 to NO3 depletion in the glacial Southern Ocean. Geophys. Res. Lett. 29, 1564 (2002)

Download references

Author information

Affiliations

  1. Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, California 90095, USA

    • Thomas S. Weber &
    • Curtis Deutsch

Contributions

T.S.W. conducted the simulations and analysed the results. C.D. designed the study. Both authors wrote the paper.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Supplementary information

PDF files

  1. Supplementary Information (4.1M)

    This file contains Supplementary Methods, Supplementary Tables 1-3, Supplementary Notes on sensitivity testing, Supplementary Figures 1-6 with legends and additional references.

Additional data