Phosphate depletion in the western North Atlantic Ocean.

Surface waters of the subtropical Sargasso Sea contain dissolved inorganic phosphate (DIP) concentrations of 0.2 to 1.0 nanomolar, which are sufficiently low to result in phosphorus control of primary production. The DIP concentrations in this area (which receives high inputs of iron-rich dust from arid regions of North Africa) are one to two orders of magnitude lower than surface levels in the North Pacific (where eolian iron inputs are much lower and water column denitrification is much more substantial). These data indicate a severe relative phosphorus depletion in the Atlantic. We hypothesize that nitrogen versus phosphorus limitation of primary production in the present-day ocean may be closely linked to iron supply through control of dinitrogen (N2) fixation, an iron-intensive metabolic process. Although the oceanic phosphorus inventory may set the upper limit for the total amount of organic matter produced in the ocean over geological time scales, at any instant in geological time, oceanic primary production may fall below this limit because of a persistent insufficient iron supply. By controlling N2 fixation, iron may control not only nitrogen versus phosphorus limitation but also carbon fixation and export stoichiometry and hence biological sequestration of atmospheric carbon dioxide.

[1]  J. P. Grime,et al.  The response of two contrasting limestone grasslands to simulated climate change. , 2000, Science.

[2]  Paul G. Falkowski,et al.  Evolution of the nitrogen cycle and its influence on the biological sequestration of CO2 in the ocean , 1997, Nature.

[3]  W. Thomas.  Phytoplankton Nutrient Enrichment Experiments off Baja California and in the Eastern Equatorial Pacific Ocean , 1969 .

[4]  D. Karl,et al.  Temporal variability in dissolved phosphorus concentrations in the subtropical North Pacific Ocean , 1997 .

[5]  E. Prepas,et al.  Relative importance of iron and molybdenum in restricting phytoplankton biomass in high phosphorus saline lakes , 1997 .

[6]  Y. Fujita,et al.  THE EFFECT OF IRON NUTRITION ON PHOTOSYNTHESIS AND NITROGEN FIXATION IN CULTURES OF TRICHODESMIUM (CYANOPHYCEAE) 1 , 1990 .

[7]  B. Peterson,et al.  Particulate organic matter flux and planktonic new production in the deep ocean , 1979, Nature.

[8]  J. G. Field,et al.  The Ecological Role of Water-Column Microbes in the Sea* , 1983 .

[9]  F. A. Richards,et al.  An analysis of the horizontal regime of denitrification in the eastern tropical North Pacific1 , 1976 .

[10]  B. Hicks,et al.  The atmospheric input of trace species to the world ocean , 1991 .

[11]  W. Sunda,et al.  Feedback interactions between zinc and phytoplankton in seawater , 1992 .

[12]  J. Stockner,et al.  Response of Anabaena and Synechococcus to manipulation of nitrogen: phosphorus ratios in a lake fertilization experiment , 1988 .

[13]  J. Schnoor,et al.  Nitrogen fixation: Anthropogenic enhancement‐environmental response , 1995 .

[14]  Farooq Azam,et al.  Microbial Control of Oceanic Carbon Flux: The Plot Thickens , 1998, Science.

[15]  Nicolas Gruber,et al.  Global patterns of marine nitrogen fixation and denitrification , 1997 .

[16]  D. Schindler.  Evolution of phosphorus limitation in lakes. , 1977, Science.

[17]  Toby Tyrrell,et al.  The relative influences of nitrogen and phosphorus on oceanic primary production , 1999, Nature.

[18]  D. Hutchins,et al.  Interaction of iron and major nutrients controls phytoplankton growth and species composition in the tropical North Pacific Ocean , 1993 .

[19]  Wallace S. Broecker,et al.  The sequence of events surrounding Termination II and their implications for the cause of glacial‐interglacial CO2 changes , 1998 .

[20]  J. Rueter.  IRON STIMULATION OF PHOTOSYNTHESIS AND NITROGEN FIXATION IN ANABAENA 7120 AND TRICHODESMIUM (CYANOPHYCEAE) 1 , 1988 .

[21]  M. McElroy,et al.  Marine biological controls on atmospheric CO2 and climate , 1983, Nature.

[22]  A. Longhurst.  Role of the marine biosphere in the global carbon cycle , 1991 .

[23]  E. Carpenter,et al.  Marine pelagic cyanobacteria : Trichodesmium and other diazotrophs , 1992 .

[24]  G. Jackson,et al.  Importance of dissolved organic nitrogen and phosphorus to biological nutrient cycling , 1985 .

[25]  D. Karl,et al.  MAGIC : a sensitive and precise method for measuring dissolved phosphorus in aquatic environments , 1992 .

[26]  M. Behrenfeld,et al.  Widespread iron limitation of phytoplankton in the south pacific ocean , 1999, Science.

[27]  P. Renaud,et al.  Distributions of TOP, TON and TOC in the North Pacific subtropical gyre : Implications for nutrient supply in the surface ocean and remineralization in the upper thermocline , 2000 .

[28]  F. A. Richards,et al.  OXYGEN DEFICIENT CONDITIONS AND NITRATE REDUCTION IN THE EASTERN TROPICAL NORTH PACIFIC OCEAN1 , 1972 .

[29]  J. Raven.  The iron and molybdenum use efficiencies of plant growth with different energy, carbon and nitrogen sources , 1988 .

[30]  H. Paerl,et al.  Iron-Stimulated N2 Fixation and Growth in Natural and Cultured Populations of the Planktonic Marine Cyanobacteria Trichodesmium spp , 1994, Applied and environmental microbiology.

[31]  L. Codispoti,et al.  Nitrification, denitrification and nitrous oxide cycling in the eastern tropical South Pacific ocean , 1985 .

[32]  L. Codispoti.  Is the ocean losing nitrate? , 1995, Nature.

[33]  J. P. Riley,et al.  A modified single solution method for the determination of phosphate in natural waters , 1962 .

[34]  Jorge L. Sarmiento,et al.  Redfield ratios of remineralization determined by nutrient data analysis , 1994 .

[35]  Ricardo M Letelier,et al.  The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean , 1997, Nature.

[36]  K. Fanning.  Nutrient provinces in the sea: Concentration ratios, reaction rate ratios, and ideal covariation , 1992 .

[37]  D. Karl,et al.  Application of a novel method for phosphorus determinations in the oligotrophic North Pacific Ocean , 1998 .

[38]  R. Ganeshram,et al.  Large changes in oceanic nutrient inventories from glacial to interglacial periods , 1995, Nature.

[39]  S. V. Smith.  Phosphorus versus nitrogen limitation in the marine environment1 , 1984 .

[40]  R. Duce,et al.  Atmospheric transport of iron and its deposition in the ocean , 1991 .

[41]  P. Falkowski,et al.  Biogeochemical Controls and Feedbacks on Ocean Primary Production , 1998, Science.

[42]  J. Toggweiler.  Oceanography: An ultimate limiting nutrient , 1999, Nature.

[43]  Edward J. Carpenter,et al.  Trichodesmium, a Globally Significant Marine Cyanobacterium , 1997 .

[44]  J. Sarmiento,et al.  Inputs, losses and transformations of nitrogen and phosphorus in the pelagic North Atlantic Ocean , 1996 .

[45]  Stephen V. Smith,et al.  Vertical flux and biogeochemical turnover regulate nutrient limitation of net organic production in the North Pacific Gyre , 1986 .

[46]  James N. Galloway,et al.  Atmospheric deposition of nutrients to the North Atlantic Basin. , 1996 .

[47]  W. Prell,et al.  Climate-related variations in denitrification in the Arabian Sea from sediment 15N/14N ratios , 1995, Nature.

[48]  Raphael Kudela,et al.  A massive phytoplankton bloom induced by an ecosystem-scale iron fertilization experiment in the equatorial Pacific Ocean , 1996, Nature.

[49]  E. Carpenter,et al.  Major Role of the Cyanobacterium Trichodesmium in Nutrient Cycling in the North Atlantic Ocean , 1991, Science.