The biogeochemical cycle of iron in the ocean


Advances in iron biogeochemistry have transformed our understanding of the oceanic iron cycle over the past three decades: multiple sources of iron to the ocean were discovered, including dust, coastal and shallow sediments, sea ice and hydrothermal fluids. This new iron is rapidly recycled in the upper ocean by a range of organisms; up to 50% of the total soluble iron pool is turned over weekly in this way in some ocean regions. For example, bacteria dissolve particulate iron and at the same time release compounds — iron-binding ligands — that complex with iron and therefore help to keep it in solution. Sinking particles, on the other hand, also scavenge iron from solution. The balance between these supply and removal processes determines the concentration of dissolved iron in the ocean. Whether this balance, and many other facets of the biogeochemical cycle, will change as the climate warms remains to be seen.

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Figure 1: Dissolved iron vertical profiles illustrating aspects of supply and removal processes.
Figure 2: Size-partitioning of iron and iron-binding ligands with depth.
Figure 3: Modification of aerosol iron upon entering surface waters.
Figure 4: Multiple sources of new iron to the Southern Ocean.
Figure 5: Biological iron recycling in the upper ocean.
Figure 6: The influence of particle scavenging and remineralization on dissolved iron concentrations in three zones (0–250 m (blue), 250–1,000 m (orange) and >1,000 m (grey)) denoted in panels ac.


  1. 1

    Martin, J. H. & Gordon, R. M. Northeast Pacific iron distributions in relation to phytoplankton productivity. Deep Sea Res. A. Oceanogr. Res. Papers 35, 177–196 (1988).

  2. 2

    Martin, J. H., Gordon, R. M., Fitzwater, S. & Broenkow, W. W. VERTEX: Phytoplankton/iron studies in the Gulf of Alaska. Deep Sea Res. A. Oceanogr. Res. Papers 36, 649–680 (1989).

  3. 3

    Martin, J. H. Glacial-interglacial CO2 change: the iron hypothesis. Paleoceanography 5, 1–13 (1990).

  4. 4

    Martin, J. H. & Fitzwater, S. E. Iron-deficiency limits phytoplankton growth in the Northeast Pacific Subarctic. Nature 331, 341–343 (1988).

  5. 5

    de baar, H. J. W. et al. On iron limitation of the Southern Ocean — experimental-observations in the Weddell and Scotia Seas. Mar. Ecol. Prog. Ser. 65, 105–122 (1990).

  6. 6

    Schaule, B. K. & Patterson, C. C. Lead concentrations in the northeast Pacific: evidence for global anthropogenic perturbations. Earth Planet. Sci. Lett. 54, 97–116 (1981).

  7. 7

    Bruland, K. W., Donat, J. R. & Hutchins, D. A. Interactive influences of bioactive trace metals on biological production in oceanic waters. Limnol. Oceanogr. 36, 1555–1577 (1991).

  8. 8

    Gordon, R. M., Martin, J. H. & Knauer, G. A. Iron in northeast Pacific waters. Nature 299, 611–612 (1982).

  9. 9

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

  10. 10

    de Baar, H. J. W. et al. Synthesis of iron fertilization experiments: from the Iron Age in the Age of Enlightenment. J. Geophys. Res. Oceans 110, C09S16 (2005).

  11. 11

    Moore, J. K., Doney, S. C., Glover, D. M. & Fung, I. Y. Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean. Deep-Sea Res. 49, 463–507 (2001).

  12. 12

    Moore, C. M. et al. Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability. Nature Geosci. 2, 867–871 (2009).

  13. 13

    Boyd, P. W. et al. The decline and fate of an iron-induced subarctic phytoplankton bloom. Nature 428, 549–553 (2004).

  14. 14

    Sigman, D. M. & Boyle, E. A. Glacial/interglacial variations in atmospheric carbon dioxide. Nature 407, 859–869 (2000).

  15. 15

    Wedepohl, K. H. The composition of the continental crust. Geochim. Cosmochim. Acta 59, 1217–1232 (1995).

  16. 16

    Landing, W. M. & Bruland, K. W. The contrasting biogeochemistry of iron and manganese in the Pacific Ocean. Geochim. Cosmochim. Acta 51, 29–43 (1987).

  17. 17

    Martin, J. H., Fitzwater, S. E., Gordon, R. M., Hunter, C. N. & Tanner, S. J. Iron, primary production and carbon nitrogen flux studies during the JGOFS North Atlantic Bloom Experiment. Deep-Sea Res. 40, 115–134 (1993).

  18. 18

    Kuma, K., Nishioka, J. & Matsunaga, K. Controls on iron(III) hydroxide solubility in seawater: the influence of pH and natural organic chelators. Limnol. Oceanogr. 41, 396–407 (1996).

  19. 19

    Johnson, K. S., Gordon, R. M. & Coale, K. H. What controls dissolved iron concentrations in the world ocean? Mar. Chem. 57, 137–161 (1997).

  20. 20

    Liu, X. & Millero, F. J. The solubility of iron in seawater. Mar. Chem. 77, 43–54 (2002).

  21. 21

    Wu, J. F., Boyle, E., Sunda, W. & Wen, L. S. Soluble and colloidal iron in the oligotrophic North Atlantic and North Pacific. Science 293, 847–849 (2001).

  22. 22

    Boyle, E. What controls dissolved iron concentrations in the world ocean? A comment. Mar. Chem. 57, 163–167 (1997).

  23. 23

    de Baar, H. J. W. & de Jong, J. T. M. in The Biogeochemistry of Iron in Seawater Vol. 7 (eds Turner, D. R. & Hunter, K. A.) (Wiley, 2001).

  24. 24

    Measures, C. I., Landing, W. M., Brown, M. T. & Buck, C. S. High-resolution Al and Fe data from the Atlantic Ocean CLIVAR-CO2 Repeat Hydrography A16N transect: Extensive linkages between atmospheric dust and upper ocean geochemistry. Glob. Biogeochem. Cycles 22, GB1005 (2008).

  25. 25

    Bergquist, B. A., Wu, J. & Boyle, E. A. Variability in oceanic dissolved iron is dominated by the colloidal fraction. Geochim. Cosmochim. Acta 71, 2960–2974 (2007).

  26. 26

    Nishioka, J., Takeda, S., Wong, C. S. & Johnson, W. Size-fractionated iron concentrations in the northeast Pacific Ocean: distribution of soluble and small colloidal iron. Mar. Chem. 74, 157–179 (2001).

  27. 27

    Bruland, K. W., Orians, K. J. & Cowen, J. P. Reactive trace metals in the stratified Central North Pacific. Geochim. Cosmochim. Acta 58, 3171–3182 (1994).

  28. 28

    Brown, M. T., Landing, W. M. & Measures, C. I. Dissolved and particulate Fe in the western and central North Pacific: results from the 2002 IOC cruise. Geochem. Geophys. Geosyst. 6, Q10001 (2005).

  29. 29

    Gordon, R. M., Coale, K. H. & Johnson, K. S. Iron distributions in the equatorial Pacific: implications for new production. Limnol. Oceanogr. 42, 419–431 (1997).

  30. 30

    Johnson, W. K., Miller, L. A., Sutherland, N. E. & Wong, C. S. Iron transport by mesoscale Haida eddies in the Gulf of Alaska. Deep-Sea Res. II 52, 933–953 (2005).

  31. 31

    Johnson, K. S. et al. Developing standards for dissolved iron in seawater. Eos 88, 131–132 (2007).

  32. 32

    Millero, F. J., Sotolongo, S. & Izaguirre, M. The oxidation kinetics of Fe(II) in seawater. Geochim. Cosmochim. Acta 51, 793–801 (1987).

  33. 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).

  34. 34

    Mawji, E. et al. Hydroxamate siderophores: Occurrence and importance in the Atlantic Ocean. Envir. Sci. Technol. 42, 8675–8680 (2008).

  35. 35

    Boyd, P. W., Ibisanmi, E., Sander, S., Hunter, K. A. & Jackson, G. A. Remineralization of upper ocean particles: implications for iron biogeochemistry. Limnol. Oceanogr. 55, 1271–1288 (2010).

  36. 36

    Amin, S. A. et al. Photolysis of iron-siderophore chelates promotes bacterial-algal mutualism. Proc. Natl Acad. Sci. USA 106, 17071–17076 (2009).

  37. 37

    Barbeau, K. A., Rue, E. L., Bruland, K. W. & Butler, A. Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands. Nature 413, 409–413 (2001).

  38. 38

    Cullen, J. T., Bergquist, B. A. & Moffett, J. W. Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean. Mar. Chem. 98, 295–303 (2006).

  39. 39

    Baker, A. R. & Croot, P. L. Atmospheric and marine controls on aerosol iron solubility in seawater. Mar. Chem. 120, 4–13 (2010).

  40. 40

    Wu, J. F. & Boyle, E. A. Iron in the Sargasso Sea: implications for the processes controlling dissolved Fe distribution in the ocean. Glob. Biogeochem. Cycles 16, 1086 (2002).

  41. 41

    Prospero, J., Uematsu, M. & Savoie, D. in Chemical Oceanography Vol. 10 (ed. Riley, J. P.) 187–218 (Academic, 1989).

  42. 42

    Duce, R. A. & Tindale, N. W. Atmospheric transport of iron and its deposition in the ocean. Limnol. Oceanogr. 36, 1715–1726 (1991).

  43. 43

    de Baar, H. J. W. et al. Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern Ocean. Nature 373, 412–415 (1995).

  44. 44

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

  45. 45

    Smith, J. et al. Free-drifting icebergs: hot spots of chemical and biological enrichment in the Weddell Sea. Science 317, 478–482 (2007).

  46. 46

    Lannuzel, D. et al. Iron study during a time series in the western Weddell pack ice. Mar. Chem. 108, 85–95 (2008).

  47. 47

    Klunder, P., Laan, P., Middag, R., de Baar, H. J. W. & van Ooijen, J. Dissolved iron in the Southern Ocean (Atlantic Sector) Deep-Sea Res. II: (in press).

  48. 48

    Bowie, A. R. et al. Biogeochemical iron budgets of the Southern Ocean south of Australia: decoupling of iron and nutrient cycles in the subantarctic zone by the summertime supply. Glob. Biogeochem. Cycles 23, GB4034 (2009).

  49. 49

    Blain, S. et al. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean. Nature 446, 1070–1074 (2007).

  50. 50

    Boyd, P. W. et al. FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters. Glob. Biogeochem. Cycles 19, GB4S20 (2005).

  51. 51

    Gaiero, D. M., Probst, J. L., Depetris, P. J., Bidart, S. M. & Leleyter, L. Iron and other transition metals in Patagonian riverborne and windborne materials: geochemical control and transport to the southern South Atlantic Ocean. Geochim. Cosmochim. Acta 67, 3603–3623 (2003).

  52. 52

    Sokolov, S. & Rintoul, S. R. On the relationship between fronts of the Antarctic Circumpolar Current and surface chlorophyll concentrations in the Southern Ocean. J. Geophys. Res. 112, C07030 (2007).

  53. 53

    Elrod, V. A., Berelson, W. M., Coale, K. H. & Johnson, K. S. The flux of iron from continental shelf sediments: a missing source for global budgets. Geophys. Res. Lett. 31, L12307 (2004).

  54. 54

    Johnson, K. S., Chavez, F. P. & Friederich, G. E. Continental-shelf sediments as a primary source of iron for coastal phytoplankton. Nature 398, 697–700 (1999).

  55. 55

    Wetz, M. S., Burke, H., Chase, Z., Wheeler, P. A. & Whitney, M. M. Riverine input of macronutrients, iron, and organic matter to the coastal ocean off Oregon, USA, during the winter. Limnol. Oceanogr. 51, 2221–2231 (2006).

  56. 56

    Nishioka, J. et al. Iron supply to the western subarctic Pacific: Importance of iron export from the Sea of Okhotsk. J. Geophys. Res. 112, C10012 (2007).

  57. 57

    Mackenzie, F. T., Lantzy, R. & Paterson, V. Global trace metal cycles and predictions. J. Int. Assoc. Math. Geol. 11, 99–142 (1979).

  58. 58

    Boyle, E. A., Edmond, J. M. & Sholkovitz, E. R. Mechanism of iron removal in estuaries. Geochim. Cosmochim. Acta 41, 1313–1324 (1977).

  59. 59

    Johnson, K. S. Iron supply and demand in the upper ocean: is extraterrestrial dust a significant source of bioavailable iron? Glob. Biogeochem. Cycles 15, 61–63 (2001).

  60. 60

    Sedwick, P. N., Sholkovitz, E. R. & Church, T. M. Impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron: evidence from the Sargasso Sea. Geochem. Geophys. Geosyst. 8, Q10Q06 (2007).

  61. 61

    Luo, C. et al. Combustion iron distribution and deposition. Global Biogeochem. Cycles 22, GB1012 (2008).

  62. 62

    Boyd, P. W., Mackie, D. S. & Hunter, K. A. Aerosol iron deposition to the surface ocean: modes of iron supply and biological responses. Mar. Chem. 120, 128–143 (2010).

  63. 63

    Jickells, T. D. et al. Global iron connections between desert dust, ocean biogeochemistry, and climate. Science 308, 67–71 (2005).

  64. 64

    Price, N. M. & Morel, F. M. M. in Iron Transport and Storage in Microorganisms, Plants, and Animals Vol. 35 Metal Ions in Biological Systems, 1–36 (CRC, 1998).

  65. 65

    Brand, L. E., Sunda, W. G. & Guillard, R. R. L. Limitation of marine phytoplankton reproductive rates by zinc, manganese, and iron. Limnol. Oceanogr. 28, 1182–1198 (1983).

  66. 66

    Hutchins, D. A. & Bruland, K. W. Grazer-mediated regeneration and assimilation of Fe, Zn and Mn from planktonic prey. Mar. Ecol. Progr. Ser. 110, 259–269 (1994).

  67. 67

    Lee, B-G. & Fisher, N. S. Release rates of trace elements and protein from decomposing planktonic debris. 1. Phytoplankton debris. J. Plankt. Res. 51, 391–421 (1993).

  68. 68

    Kirchman, D. L. Microbial ferrous wheel. Nature 383, 303–304 (1996).

  69. 69

    Haygood, M. G., Holt, P. D. & Butler, A. Aerobactin production by a planktonic marine Vibrio sp. Limnol. Oceanogr. 38, 1091–1097 (1993).

  70. 70

    Wilhelm, S. W. The ecology of cyanobacteria in iron-limited environments: a review of physiology and implications for aquatic environments. Aquat. Microb. Ecol. 9, 295–303 (1995).

  71. 71

    Sunda, W. G. in The Biogeochemistry of Iron in Seawater (eds Turner, D. R. & Hunter, K. A.) 41–84 (Wiley, 2001).

  72. 72

    Hudson, R. J. M. & Morel, F. M. M. Iron transport in marine-phytoplankton — kinetics of cellular and medium coordination reactions. Limnol. Oceanogr. 35, 1002–1020 (1990).

  73. 73

    Shaked, Y., Kustka, A. B. & Morel, F. M. M. A general kinetic model for iron acquisition by eukaryotic phytoplankton. Limnol. Oceanogr. 50, 872–882 (2005).

  74. 74

    Nodwell, L. M. & Price, N. M. Direct use of inorganic colloidal iron by marine mixotrophic phytoplankton. Limnol. Oceanogr. 46, 765–777 (2001).

  75. 75

    Strzepek, R. F. et al. Spinning the 'Ferrous Wheel': the importance of the microbial community in an iron budget during the FeCycle experiment. Glob. Biogeochem. Cycles 19, GB4S26 (2005).

  76. 76

    Barbeau, K., Moffett, J. W., Caron, D. A., Croot, P. L. & Erdner., D. L. Role of protozoan grazing in relieving iron limitation of phytoplankton. Nature 380, 61–64 (1996).

  77. 77

    Maranger, R., Bird, D. F. & Price, N. M. Iron acquisition by photosynthetic marine phytoplankton from ingested bacteria. Nature 396, 248–251 (1998).

  78. 78

    Sarthou, G. et al. The fate of biogenic iron during a phytoplankton bloom induced by natural fertilisation: Impact of copepod grazing. Deep-Sea Res. II 55, 734–752 (2008).

  79. 79

    Mioni, C. E., Poorvin, L. & Wilhelm, S. W. Virus and siderophore-mediated transfer of available Fe between heterotrophic bacteria: characterization using an Fe-specific bioreporter. Aquat. Microb. Ecol. 41, 233–245 (2005).

  80. 80

    Frew, R. D. et al. Particulate iron dynamics during FeCycle in subantarctic waters southeast of New Zealand. Glob. Biogeochem. Cycles 20, GB1S93 (2006).

  81. 81

    Lamborg, C. H., Buesseler, K. O. & Lam, P. J. Sinking fluxes of minor and trace elements in the North Pacific Ocean measured during the VERTIGO program. Deep-Sea Res. II 55, 1564–1577 (2008).

  82. 82

    Sunda, W. G. & Huntsman, S. A. Interrelated influence of iron, light, and cell size on marine phytoplankton growth. Nature 390, 389–392 (1997).

  83. 83

    Bowie, A. R. et al. The fate of added iron during a mesoscale fertilisation experiment in the Southern Ocean. Deep-Sea Res. II 48, 2703–2743 (2001).

  84. 84

    Chever, F., Sarthou, G., Bucciarelli, E., Blain, S. & Bowie, A. R. An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean). Biogeosciences 7, 455–468 (2010).

  85. 85

    Weber, L., Völker, C., Schartau, M. & Wolf-Gladrow, D. A. Modeling the speciation and biogeochemistry of iron at the Bermuda Atlantic Time-series Study site. Glob. Biogeochem. Cycles 19, GB1019 (2005).

  86. 86

    Archer, D. E. & Johnson, K. S. A model of the iron cycle in the ocean. Glob. Biogeochem. Cycles 14, 269–279 (2002).

  87. 87

    Parekh, P., Follows, M. J. & Boyle, E. Modeling the global ocean iron cycle. Glob. Biogeochem. Cycles 18, GB1002 (2004).

  88. 88

    Gnanadesikan, A., Sarmiento, J. L. & Slater, R. D. Effects of patchy ocean fertilization on atmospheric carbon dioxide and biological production. Glob. Biogeochem. Cycles 17, 1050 (2003).

  89. 89

    Homoky, W. S., Severmann, S., Mills, R., Statham, P. & Fones, G. Pore-fluid Fe isotopes reflect the extent of benthic Fe redox recycling: evidence from continental shelf and deep-sea sediments. Geology 37, 751–754 (2009).

  90. 90

    Lacan, F. et al. Measurement of the isotopic composition of dissolved iron in the open ocean. Geophys. Res. Lett. 35, L24610 (2008).

  91. 91

    Kitayama, S. et al. Controls on iron distributions in the deep water column of the North Pacific Ocean: Iron(III) hydroxide solubility and marine humic-type dissolved organic matter. J. Geophys. Res. 114, C08019 (2009).

  92. 92

    Boyle, E. A., Bergquist, B. A., Kayser, R. A. & Mahowald, N. Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA: temporal variability and an intermediate water hydrothermal plume. Geochim. Cosmochim. Acta 69, 933–952 (2005).

  93. 93

    Borer, P. M., Sulzberger, B., Reichard, P. & Kraemer, S. M. Effect of siderophores on the light-induced dissolution of colloidal iron(III) (hydr)oxides. Mar. Chem. 93, 179–193 (2005).

  94. 94

    Croot, P. L., Streu, P. & Baker, A. R. Short residence time for iron in surface seawater impacted by atmospheric dry deposition from Saharan dust events. Geophys. Res. Lett. 31, L23S08 (2004).

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We thank A. Bowie (Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania) for providing unpublished dissolved iron data from the Southern Ocean (Fig. 1a), and L. Bucke (Department of Chemistry, University of Otago) for help with the graphics. We thank S. Solokov and S. Rintoul (CSIRO, Hobart, Tasmania) and G. Jackson (Texas A&M) for providing personal communications regarding bottom pressure torque and vertical changes in particle surface area, respectively.

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Boyd, P., Ellwood, M. The biogeochemical cycle of iron in the ocean. Nature Geosci 3, 675–682 (2010).

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