Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
6
10
2009
10.5194/bg-6-2041-2009
http://www.biogeosciences.net/6/2041/2009/
http://www.biogeosciences.net/6/2041/2009/bg-6-2041-2009.html
http://www.biogeosciences.net/6/2041/2009/bg-6-2041-2009.pdf
2041
2061
2009-10-07
A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory site
Y. Ye
ying.ye@awi.de
C. Völker
D. A. Wolf-Gladrow
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
A one-dimensional model of Fe speciation and biogeochemistry,
coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type
ecosystem model, is applied for the Tropical
Eastern North Atlantic Time-Series Observatory (TENATSO)
site. Among diverse processes affecting Fe speciation, this
study is focusing on investigating the role of dust particles in
removing dissolved iron (DFe) by a more complex description of particle
aggregation and sinking, and explaining the abundance of organic
Fe-binding ligands by modelling their origin and fate.
<br><br>
The vertical distribution of different particle classes in the model shows high
sensitivity to changing aggregation rates. Using the aggregation
rates from the sensitivity study in this work, modelled particle
fluxes are close to observations, with dust particles dominating near the surface and
aggregates deeper in the water column. POC export at 1000 m is
a little higher than regional sediment trap measurements, suggesting
further improvement of modelling particle aggregation, sinking or
remineralisation.
<br><br>
Modelled strong ligands have a high abundance near the surface and decline
rapidly below the deep chlorophyll maximum, showing qualitative similarity
to observations. Without production of strong
ligands, phytoplankton concentration falls to 0 within the first 2 years
in the model integration, caused by strong Fe-limitation. A nudging of total weak
ligands towards a constant value is required for reproducing the
observed nutrient-like profiles, assuming a decay
time of 7 years for weak ligands. This indicates that weak ligands
have a longer decay time and therefore cannot be modelled adequately
in a one-dimensional model.
<br><br>
The modelled DFe profile is strongly influenced by particle
concentration and vertical distribution, because the most important
removal of DFe in deeper waters is colloid formation and
aggregation. Redissolution of particulate iron is required to
reproduce an observed DFe profile at TENATSO site. Assuming colloidal iron
is mainly composed of inorganic colloids, the modelled colloidal to
soluble iron ratio is lower that observations, indicating the
importance of organic colloids.
Amon, R. and Benner, R.: Rapid cycling of high-molecular-weight dissolved organic matter in the ocean, Nature, 369, 549–552, 1994.
Armstrong, R., Lee, C., Hedges, J., Honjo, S., and Wakeham, S.: A new, mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of POC with ballast minerals, Deep-Sea Res. II, 49, 219–236, 2002.
Asper, V. and Smith, W J.: Abundance, distribution and sinking rates of aggregates in the Ross Sea, Antarctica, Deep-Sea Res. I, 50, 131–150, \doi10.1016/S0967-0637(02)00146-2, 2003.
Asper, V., Deuser, W., Knauer, G., and Lohrenz, S.: Rapid coupling of sinking particle fluxes between surface and deep ocean waters, Nature, 357, 670–672, 1992.
Aumont, O., Maier-Reimer, E., Blain, S., and Monfray, P.: An ecosystem model of the global ocean including Fe, Si, P colimitations, Global Biogeochem. Cy., 17, 1060, \doi10.1029/2001GB001745, 2003.
Bacon, M P. and Anderson, R F.: Distribution of thorium isotopes between dissolved and particulate forms in the deep sea, J. Geophys. Res., 87(C3), 2045–2056, \doi10.1029/JC087iC03p02045, 1982.
Baker, A., Jickells, T., Biswas, K., Weston, K., and French, M.: Nutrients in atmospheric aerosol particles along the Atlantic Meridional Transect, Deep Sea Res. II, 53, 1706–1719, \doi10.1016/j.dsr2.2006.05.012, 2006a.
Baker, A., Jickells, T., Witt, M., and Linge, K.: Trends in the solubility of iron, aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean, Mar. Chem., 98, 43–58, 2006b.
Baker, A R. and Jickells, T D.: Mineral particle size as a control on aerosol iron solubility, Geophys. Res. Lett., 33, L17608, \doi10.1029/2006GL026557, 2006.
Balistieri, L., Brewer, P., and Murray, J.: Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean, Deep Sea Res., 28A, 101–121, 1981.
Barbeau, K. and Moffett, J.: Laboratory and field studies of colloidal iron oxide dissolution as mediated by phagotrophy and photolysis, Limnol. Oceanogr., 45(4), 827–835, 2000.
Barbeau, K., Rue, E., Bruland, K., and Butler, A.: Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands, Nature, 413, 409–413, 2001.
Barbeau, K., Rue, E., Trick, C., Bruland, K., and Butler, A.: Photochemical reactivity of siderophores produced by marine heterotrophic bacteria and cyanobacteria based on characteristic Fe(III) binding groups, Limnol. Oceanogr., 48, 1069–1078, 2003.
Behrenfeld, M. and Falkowski, P.: Photosynthetic rates derived from satellite-based chlorophyll concentration, Limnol. Oceanogr., 42, 1–20, 1997.
Bergquist, B., Wu, J., and Boyle, E.: Variability in oceanic dissolved iron is dominated by the colloidal fraction, Geochim. Cosmochim. Ac., 71, 2960–2974, \doi10.1016/j.gca.2007.03.013, 2007.
Bory, A., Jeandel, C., Leblond, N., Vangriesheim, A., Khripounoff, A., Beaufort, L., Rabouille, C., Nicolas, E., Tachikawa, K., Etcheber, H., and Buat-Ménard, P.: Downward particle fluxes within different productivity regimes off the Mauritanian upwelling zone (EUMELI program), Deep Sea Res. I, 48, 2251–2282, 2001.
Boyd, P W., Jickells, T., Law, C S., Blain, S., Boyle, E A., Buesseler, K O., Coale, K H., Cullen, J J., de~Baar, H. J W., Follows, M., Harvey, M., Lancelot, C., Levasseur, M., Owens, N. P J., Pollard, R., Rivkin, R B., Sarmiento, J., Schoemann, V., Smetacek, V., Takeda, S., Tsuda, A., Turner, S., and Watson, A J.: Mesoscale Iron Enrichment Experiments 1993–2005: Synthesis and Future Directions, Science, 315, 612–617, 2007.
Boye, M., Van~den Berg, C., De~Jong, J., Leach, H., Croot, P., and De~Baar, H.: Organic complexation of iron in the Southern Ocean, Deep-Sea Res. I, 48, 1477–1497, 2001.
Boye, M., Aldrich, A., van~den Berg, C., de~Jong, J., Nirmaier, H., Veldhuis, M., Timmermans, K., and de~Baar, H.: The chemical speciation of iron in the north-east Atlantic Ocean, Deep-Sea Res. I, 53, 667–683, 2006.
Broecker, W S. and Peng, T.-H.: Tracers in the sea, in: Tracers in the sea, Eldigio Press Lamont Doherty Geological Observatory, 2–5, 1982.
Burchard, H. and Umlauf, L.: Observations and numerical modelling of mixed-layer turbulence: Do they represent the same statistical quantities?, Deep Sea Res. II, 52, 1069–1074, \doi10.1016/j.dsr2.2005.03.002, 2005.
Burchard, H., Delersnijder, E., and Meister, A.: Application of modified Patankar schemes to stiff biogeochemical models for the water column, Ocean Dynam., 55, 326–337, 2005.
Burd, A. and Jackson, G.: Particle Aggregation, Annu. Rev. Mar. Sci., 1, 65–90, \doi10.1146/annurev.marine.010908.163904, 2009.
Carpenter, E J., Subramaniam, A., and Capone, D G.: Biomass and primary productivity of the cyanobacterium Trichodesmium spp. in the tropical N Atlantic ocean, Deep Sea Res. I, 51, 173–203, 2004.
Chiapello, I., Bergametti, G., Chatenet, B., Bousquet, P., Dulac, F., and Soares, E S.: Origins of African dust transported over the northeastern tropical Atlantic, J. Geophys. Res., 102(D12), 13701–13709, 1997.
Cloern, J E., Grenz, C., and Vidergar-Lucas, L.: An empirical model of the phytoplankton chlorophyll : carbon ratio-the conversion factor between productivity and growth rate, Limnol. Oceanogr., 40(7), 1313–1321, 1995.
Cullen, J., Bergquist, B., and Moffett, J.: Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean, Mar. Chem., 98, 295–303, 2006.
De~Boyer~Montegut, C Madec, G., Fischer, A., Lazar, A., and Iudicone, D.: Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology, J. Geophys. Res. C. Oceans, 109, C12003, \doi10.1029/2004JC002378, 2004.
De~La~Rocha, C. and Passow, U.: Factors influencing the sinking of POC and the efficiency of the biological carbon pump, Deep Sea Res. II, 54, 639–658, \doi10.1016/j.dsr2.2007.01.004, 2007.
Desboeufs, K V., Losno, R., and Colin, J L.: Factors influencing aerosol solubility during cloud processes, Atmos. Environ., 35, 3529–3537, 2001.
Duce, R. and Tindale, N.: Atmospheric transport of iron and its deposition in the ocean, Limnol. Oceanogr., 36, 1715–1726, 1991.
Emery, K. and Honjo, S.: Surface suspended matter off western Africa: relations of organic matter, skeletal debris and detrital minerals, Sedimentology, 26, 775–794, 1979.
Falkowski, P.: Evolution of the nitrogen cycle and its influence on the biological sequestration of CO<sub>2</sub> in the ocean, Nature, 387, 272–275, 1997.
Fischer, G;~Ratmeyer, V. and Wefer, G.: Organic carbon fluxes in the Atlantic and the Southern Ocean: relationship to primary production compiled from satellite radiometer data, Deep-Sea Res. II, 47, 1961–1997, \doi10.1016/S0967-0645(00)00013-8, 2000.
Francois, R., Honjo, S., Krishfield, R., and Manganini, S.: Factors controlling the flux of organic carbon to the bathypelagic zone of the ocean, Global Biogeochem. Cy., 16, 1087, \doi10.1029/2001GB001722, 2002.
Gerringa, L., Veldhuis, M., Timmermans, K., Sarthou, G., and de~Baar, H.: Co-variance of dissolved Fe-binding ligands with phytoplankton characteristics in the Canary Basin, Mar. Chem., 102, 276–290, 2006.
Gerringa, L., Blain, S., Laan, P., Sarthou, G., Veldhuis, M., Brussaard, C., Viollier, E., and Timmermans, K.: Fe-binding dissolved organic ligands near the Kerguelen Archipelago in the Southern Ocean (Indian sector), Deep Sea Res. II, 55, 606–621, 2008.
Gledhill, M. and van den Berg, C.: Determination of complexation of iron(III) with natural organic complexing ligands in seawater using cathodic stripping voltammetry, Mar. Chem., 47, 41–54, 1994.
Granger, J. and Price, N M.: The importance of siderophores in iron nutrition of heterotrophic marine bacteria, Limnol. Oceanogr., 44, 541–555, 1999.
Graziano, L., Geider, R., Li, W., and Olaizola, M.: Nitrogen limitation of North Atlantic phytoplankton: analysis of physiological condition in nutrient enrichment experiments, Aquat. Microb. Ecol., 11, 53–64, 1996.
Gruber, N., Frenzel, H., Doney, S., Marchesiello, P., McWilliams, J., Moisan, J., Oram, J., Plattner, G.-K., and Stolzenbach, K.: Eddy-resolving simulation of plankton ecosystem dynamics in the California Current System, Deep Sea Res. I, 53, 1483–1516, \doi10.1016/j.dsr.2006.06.005, 2006.
Guieu, C., Bozec, Y., Blain, S., Ridame, C., Sarthou, G., and Leblond, N.: Impact of high Saharan dust inputs on dissolved iron concentrations in the Mediterranean Sea, Geophys. Res. Lett., 29, 17-1–17-4, \doi10.1029/2001GL014454, 2002.
Hamm, C.: Interactive aggregation and sedimentation of diatoms and clay-sized lithogenic material, Limnol. Oceanogr., 47, 1790–1795, 2002.
Heinold, B., Helmert, J., Hellmuth, O., Wolke, R., Ansmann, A., Marticorena, B., Laurent, B., and Tegen, I.: Regional modeling of Saharan dust events using LM-MUSCAT: Model description and case studies, J. Geophys. Res., 112, D11204, \doi10.1029/2006JD007443, 2007.
Honjo, S., Manganini, S., and Poppe, L.: Sedimentation of lithogenic particles in the deep ocean, Mar. Geol., 50, 199–220, 1982.
Hudson, R., Covault, D., and Morel, F.: Investigations of iron coordination and redox reactions in seawater using $^59$Fe radiometry and ion-pair solvent extraction of amphiphilic iron complexes, Mar. Chem., 38, 209–235, 1992.
Hunter, K A. and Boyd, P W.: Iron-binding ligands and their role in the ocean biogeochemistry of iron, Environ. Chem., 4, 221–232, 2007.
Hutchins, D., Witter, A., Butler, A., and Luther III, G.: Competition among marine phytoplankton for different chelated iron species, Nature, 400, 858–861, 1999.
Hutchins, D., Hare, C., Weaver, R., Zhang, Y., Firme, G., DiTullio, G., Alm, M., Riseman, S., Maucher, J., Geesey, M., Trick, C., Smith, G., Rue, E., Conn, J., and Bruland, K.: Phytoplankton iron limitation in the Humboldt Current and Peru Upwelling, Limnol. Oceanogr., 47, 997–1011, 2002.
Jackson, G A. and Burd, A B.: Aggregation in the Marine Environment, Environ. Sci. Technol., 32, 2805–2814, \doi10.1021/es980251w, 1998.
Jickells, T D., An, Z S., Andersen, K K., Baker, A R., Bergametti, G., Brooks, N., Cao, J J., Boyd, P W., Duce, R A., Hunter, K A., Kawahata, H., Kubilay, N., laRoche, J., Liss, P S., Mahowald, N., Prospero, J M., Ridgwell, A J., Tegen, I., and Torres, R.: Global Iron Connections Between Desert Dust, Ocean Biogeochemistry, and Climate, Science, 308, 67–71, 2005.
Johnson, K., Coale, K., Elrod, V., and Tindale, N.: Iron photochemistry in seawater from the equatorial Pacific, Mar. Chem., 46, 319–334, 1994.
Johnson, K., Gordon, R., and Coale, K.: What controls dissolved iron concentrations in the world ocean?, Mar. Chem., 57, 137–161, 1997.
Klaas, C. and Archer, D.: Association of sinking organic matter with various types of mineral ballast in the deep sea: Implications for the rain ratio, Global Biogeochem. Cy., 16, 1116, \doi10.1029/2001GB001765, 2002.
Kondo, Y., Takeda, S., Nishioka, J., Obata, H., Furuya, K., Johnson, W K., and Wong, C S.: Organic iron (III) complexing ligands during an iron enrichment experiment in the western subarctic North Pacific, Geophys. Res. Lett., 35, L12601, \doi10.1029/2008GL033354, 2008.
Kriest, I.: Different parameterizations of marine snow in a 1D-model and their influence on representation of marine snow, nitrogen budget and sedimentation, Deep-Sea Res. I, 49, 2133–2162, \doi10.1016/S0967-0637(02)00127-9, 2002.
Laglera, L M. and van~den Berg, C. M G.: Evidence for geochemical control of iron by humic substances in seawater, Limnol. Oceanogr., 54(2), 610–619, 2009.
Lewis, B., Luther, G I., Lane, H., and Church, T.: Determination of metal-organic complexation in natural waters by SWASV with pseudopolarograms, Electroanalysis, 7, 166–177, 1995.
Lutz, M., Dunbar, R., and Caldeira, K.: Regional variability in the vertical flux of particulate organic carbon in the ocean interior, Global Biogeochem. Cy., 16, 1037, \doi10.1029/2000GB001383, 2002.
Macrellis, H., Trick, C., Rue, E., Smith, G., and Bruland, K.: Collection and detection of natural iron-binding ligands from seawater, Mar. Chem., 76, 175–187, 2001.
Mahowald, N., Luo, C., Del~Corral, J., and Zender, C.: Interannual variability in atmospheric mineral aerosols from a 22-year model simulation and observational data, J. Geophys. Res.-Atmos., 108, 4352, \doi10.1029/2002JD002821, 2003.
Maldonado, M. and Price, N.: Utilization of iron bound to strong organic ligands by plankton communities in the subarctic North Pacific, Deep Sea Res. II, 46, 2447–2473, 1999.
Martin, J., Knauer, G., Karl, D., and Broenkow, W.: VERTEX: Carbon cycling in the Northeast Pacific, Deep-Sea Res. A, 34, 267–285, 1987.
Martinez, J. and Haygood, M.: Identification of a natural desferrioxamine siderophore produced by a marine bacterium, Limnol. Oceanogr. Suppl., 420–424, 2001.
Martinez, J., Carter-Franklin, J., Mann, E., Martin, J., Haygood, M., and Butler, A.: Structure and membrane affinity of a suite of amphiphilic siderophores produced by a marine bacterium, P. Natl. Acad. Sci. USA, 100, 3754–3759, \doi10.1073/pnas.0637444100, 2003.
Martinez, J S., Zhang, G P., Holt, P D., Jung, H.-T., Carrano, C J., Haygood, M G., and Butler, A.: Self-assembling amphiphilic siderophores from marine bacteria, Science, 287, 1245–1247, \doi10.1126/science.287.5456.1245, 2000.
McCave, I.: Size spectra and aggregation of suspended particles in the deep ocean, Deep-Sea Res. A, 31, 329–352, 1984.
Micinski, E., Ball, L A., and Zafiriou, O C.: Photochemical Oxygen Activation: Superoxide Radical Detection and Production Rates in the Eastern Caribbean, J. Geophys. Res., 98(C2), 2299–2306, \doi10.1029/92JC02766, 1993.
Millero, F. and Sotolongo, S.: The oxidation of Fe(II) with H<sub>2</sub>O<sub>2</sub> in seawater, Geochim. Cosmochim. Ac., 53, 1867–1873, 1989.
Mills, M., Ridame, C., Davey, M., La~Roche, J., and Geider, R.: Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic, Nature, 429, 292–294, 2004.
Moffett, J W.: Temporal and spatial variability of copper complexation by strong chelators in the Sargasso Sea, Deep Sea Res. I, 42, 1273–1295, 1995.
Morel, A., Antoine, D., Babin, M., and Dandonneau, Y.: Measured and modeled primary production in the northeast Atlantic (EUMELI JGOFS program): the impact of natural variations in photosynthetic parameters on model predictive skill, Deep Sea Res. I, 43, 1273–1304, 1996.
Parekh, P., Follows, M., and Boyle, E.: Modelling the global ocean iron cycle, Global Biogeochem. Cy., 18, GB1002, \doi1029/2003GB002061, 2004.
Passow, U.: Switching perspectives: Do mineral fluxes determine particulate organic carbon fluxes or vice versa?, Geochem. Geophy. Geosy., 5, Q04002, \doi10.1029/2003GC000670, 2004.
Passow, U. and De~la Rocha, C.: Accumulation of mineral ballast on organic aggregates, Global Biogeochem. Cy., 20, GB4S23, \doi10.1029/2005GB002579, 2006.
Powell, R. and Wilson-Finelli, A.: Photochemical degradation of organic iron complexing ligands in seawater, Aquat. Sci., 65, 367–374, 2003.
Ratmeyer, V., Fischer, G., and Wefer, G.: Lithogenic particle fluxes and grain size distributions in the deep ocean off Northwest Africa: Implications for seasonal changes of aeolian dust input and downward transport, Deep-Sea Res. I, 46, 1289–1337, \doi10.1016/S0967-0637(99)00008-4, 1999.
Reid, R., Live, D., Faulkner, D., and Butler, A.: A siderophore from a marine bacterium with an exceptional ferric ion affinity constant, Nature, 366, 455–458, 1993.
Rijkenberg, M., Powell, C., Dall'Osto, M., Nielsdottir, M., Patey, M., Hill, P., Baker, A., Jickells, T., Harrison, R., and Achterberg, E.: Changes in iron speciation following a Saharan dust event in the tropical North Atlantic Ocean, Mar. Chem., 110, 56–67, \doi10.1016/j.marchem.2008.02.006, 2008.
Rose, A. and Waite, T.: Predicting iron speciation in coastal waters from the kinetics of sunlight-mediated iron redox cycling, Aquat. Sci., 65, 375–383, 2003a.
Rose, A. and Waite, T.: Kinetics of hydrolysis and precipitation of ferric iron in seawater, Environ. Sci. Technol., 37, 3897–3903, 2003b.
Rose, A. and Waite, T.: Kinetics of iron complexation by dissolved natural organic matter in coastal waters, Mar. Chem., 84, 85–103, 2003c.
Rue, E. and Bruland, K.: 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.
Rue, E. and Bruland, K.: The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experiment, Limnol. Oceanogr., 42, 901–910, 1997.
Ruiz, J., Prieto, L., and Ortegón, F.: Diatom aggregate formation and fluxes: a modeling analysis under different size-resolution schemes and with empirically determined aggregation kernels, Deep Sea Res. I, 49, 495–515, 2002.
Sarthou, G., Baker, A., Blain, S., Achterberg, E., Boye, M., Bowie, A., Croot, P., Laan, P., De~Baar, H., Jickells, T., and Worsfold, P.: Atmospheric iron deposition and sea-surface dissolved iron concentrations in the eastern Atlantic Ocean, Deep-Sea Res. I, 50, 1339–1352, 2003.
Sarthou, G., Baker, A R., Kramer, J., Laan, P., Laës, A., Ussher, S., Achterberg, E P., de~Baar, H J., Timmermans, K R., and Blain, S.: Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean, Mar. Chem., 104, 186–202, \doi10.1016/j.marchem.2006.11.004, 2007.
Schartau, M. and Oschlies, A.: Simultaneous data-based optimization of a 1D-ecosystem model at three locations in the North Atlantic: Part I. Method and parameter estimates, J. Mar. Res., 61, 765–793, 2003a.
Schartau, M. and Oschlies, A.: Simultaneous data-based optimization of a 1D-ecosystem model at three locations in the North Atlantic: Part II. Standing stocks and nitrogen fluxes, J. Mar. Res., 61, 795–821, 2003b.
Schlosser, C. and Croot, P L.: Controls on seawater Fe(III) solubility in the Mauritanian upwelling zone, Geophys. Res. Lett., 36, L18606, \doi10.1029/2009GL038963, 2009.
Smayda, T.: The suspension and sinking of phytoplankton in the sea (RV), Ocean. Mar. Biol., 8, 353–414, 1970.
Spokes, L. and Jickells, T.: Factors controlling the solubility of aerosol trace metals in the atmosphere and on mixing into seawater, Aquat. Geochem., 1, 355–374, 1996.
Steigenberger, S. and Croot, P.: Identifying the processes controlling the distribution of H<sub>2</sub>O<sub>2</sub> in surface waters along a meridional transect in the eastern Atlantic, Geophys. Res. Lett., 35, L03616, \doi10.1029/2007GL032555, 2008.
Sunda, W. and Huntsman, S.: Iron uptake and growth limitation in oceanic and coastal phytoplankton, Mar. Chem., 50, 189–206, 1995.
Tagliabue, A., Bopp, L., Aumont, O., and Arrigo, K R.: Influence of light and temperature on the marine iron cycle: From theoretical to global modeling, Global Biogeochem. Cy., 23, GB2017, \doi10.1029/2008GB003214, 2009.
Tovar-Sanchez, A., Sañudo-Wilhelmy, S A., Garcia-Vargas, M., Weaver, R S., Popels, L C., and Hutchins, D A.: A trace metal clean reagent to remove surface-bound iron from marine phytoplankton, Mar. Chem., 82, 91–99, \doi10.1016/S0304-4203(03)00054-9, 2003.
Trick, C.: Hydroxamate-siderophore production and utilization by marine eubacteria, Current Microbiology, 18, 375–378, 1989.
Tyrrell, T., Maranon, E., Poulton, A J., Bowie, A R., Harbour, D S., and Woodward, E. M S.: Large-scale latitudinal distribution of Trichodesmium spp. in the Atlantic Ocean, J. Plankton Res., 25, 405–416, 2003.
Umlauf, L. and Burchard, H.: Second-order turbulence closure models for geophysical boundary layers. A review of recent work, Cont. Shelf Res., 25, 795–827, 2005.
Uppala, S., K\aa~llberg, P., Simmons, A., Andrae, U., da~Costa~Bechtold, V., Fiorino, M., Gibson, J., Haseler, J., Hernandez, A., Kelly, G., Li, X., Onogi, K., Saarinen, S., Sokka, N., Allan, R., Andersson, E., Arpe, K., Balmaseda, M., Beljaars, A., van~de Berg, L., Bidlot, J., Bormann, N., Caires, S., Chevallier, F., Dethof, A., Dragosavac, M., Fisher, M., Fuentes, M., Hagemann, S., Hólm, E., Hoskins, B., Isaksen, L., Janssen, P., Jenne, R., McNally, A., Mahfouf, J.-F., Morcrette, J.-J., Rayner, N., Saunders, R., Simon, P., Sterl, A., Trenberth, K., Untch, A., Vasiljevic, D., Viterbo, P., and Woollen, J.: The ERA-40 re-analysis, Q. J. Roy. Meteorol. Soc., 131, 2961–3012, \doi10.1256/qj.04.176, 2005.
van~den Berg, C.: Evidence for organic complexation of iron in seawater, Mar. Chem., 50, 139–157, 1995.
van~der Loeff, M R., Helmers, E., and Kattner, G.: Continuous transects of cadmium, copper, and aluminium in surface waters of the Atlantic Ocean, 50° N to 50° S: correspondence and contrast with nutrient-like behaviour, Geochim. Cosmochim. Ac., 61, 47–61, 1997.
Voelker, B. and Sedlak, D.: Iron reduction by photoproduced superoxide in seawater, Mar. Chem., 50, 93–102, 1995.
Wang, W.-X. and Dei, R.: Biological uptake and assimilation of iron by marine plankton: Influences of macronutrients, Mar. Chem., 74, 213–226, 2001.
Weber, L., Völker, C., Schartau, M., and Wolf-Gladrow, D.: Modeling the speciation and biogeochemistry of iron at the Bermuda Atlantic Time-series Study site, Global Biogeochem. Cy., 19, GB1019, \doi10.1029/2004GB002340, 2005.
Weber, L., Völker, C., Oschlies, A., and Burchard, H.: Iron profiles and speciation of the upper water column at the Bermuda Atlantic Time-series Study site: a model based sensitivity study, Biogeosciences, 4, 689–706, 2007.
Wedepohl, K H.: The composition of the continental crust, Geochim. Cosmochim. Ac., 59, 1217–1232, \doi10.1016/0016-7037(95)00038-2, 1995.
Wells, M. and Goldberg, E.: Colloid aggregation in seawater, Mar. Chem., 41, 353–358, 1993.
Wen, L.-S., Santschi, P., and Tang, D.: Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping, Geochim. Cosmochim. Ac., 61, 2867–2878, 1997.
Wilhelm, S. and Trick, C.: Iron-limited growth of cyanobacteria: Multiple siderophore production is a common response, Limnol. Oceanogr., 39, 1979–1984, 1994.
Wilhelm, S., Maxwell, D., and Trick, C.: Growth, iron requirements, and siderophore production in iron-limited \it Synechococcus PCC 7002, Limnol. Oceanogr., 41, 89–97, 1996.
Witter, A. and Luther III, G.: Variation in Fe-organic complexation with depth in the northwestern Atlantic Ocean as determined using a kinetic approach, Mar. Chem., 62, 241–258, 1998.
Witter, A., Lewis, B., and Luther, G I.: Iron speciation in the Arabian Sea, Deep-Sea Res. II, 47, 1517–1539, \doi10.1016/S0967-0645(99)00152-6, 2000.
Wu, J. and Boyle, E.: Iron in the Sargasso Sea: Implications for the processes controlling dissolved Fe distribution in the ocean, Global Biogeochem. Cy., 16, 1086, \doi10.1029/2001GB001453, 2002.
Wu, J., Boyle, E., Sunda, W., and Wen, L.-S.: Soluble and colloidal iron in the oligotrophic North Atlantic and North Pacific, Science, 293, 847–849, 2001.
Zielinski, O., Llinás, O., Oschlies, A., and Reuter, R.: Underwater light field and its effect on a one-dimensional ecosystem model at station ESTOC, north of the Canary Islands, Deep Sea Res. II, 49, 3529–3542, 2002.