A critical look at the calculation of the binding characteristics and concentration of iron complexing ligands in seawater with suggested improvements
Loes J. A. Gerringa A B , Micha J. A. Rijkenberg A , Charles-Edouard Thuróczy A and Leo R. M. Maas A
+ Author Affiliations
- Author Affiliations
A Royal Netherlands Institute for Sea Research, PO Box 59, NL-1790 AB Den Burg, the Netherlands.
B Corresponding author. Email: loes.gerringa@nioz.nl
Environmental Chemistry 11(2) 114-136 https://doi.org/10.1071/EN13072
Submitted: 28 March 2013 Accepted: 27 September 2013 Published: 20 March 2014
Environmental context. The low concentration of iron in the oceans limits growth of phytoplankton. Dissolved organic molecules, called ligands, naturally present in seawater, bind iron thereby increasing its solubility and, consequently, its availability for biological uptake by phytoplankton. The characteristics of these ligands are determined indirectly with various mathematical solutions; we critically evaluate the underlying method and calculations used in these determinations.
Abstract. The determination of the thermodynamic characteristics of organic Fe binding ligands, total ligand concentration ([Lt]) and conditional binding constant (K′), by means of titration of natural ligands with Fe in the presence of an added known competing ligand, is an indirect method. The analysis of the titration data including the determination of the sensitivity (S) and underlying model of ligand exchange is discussed and subjected to a critical evaluation of its underlying assumptions. Large datasets collected during the International Polar Year, were used to quantify the error propagation along the determination procedure. A new and easy to handle non-linear model written in R to calculate the ligand characteristics is used. The quality of the results strongly depends on the amount of titration points or Fe additions in a titration. At least four titration points per distinguished ligand group, together with a minimum of four titration points where the ligands are saturated, are necessary to obtain statistically reliable estimates of S, K′ and [Lt]. As a result estimating the individual concentration of two ligands, although perhaps present, might not always be justified.
References
[1] H. J. W. de Baar, A. G. J. Buma, R. F. Nolting, G. C. Cadée, G. Jacques, P. J. Tréguer, On iron limitation of the Southern Ocean: experimental observations in the Weddell and Scotia Seas Mar. Ecol. Prog. Ser. 1990, 65, 105.| On iron limitation of the Southern Ocean: experimental observations in the Weddell and Scotia SeasCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3MXhslSlt7o%3D&md5=994a5f2cda961a6d70f6e001f34271baCAS |
[2] H. J. W. de Baar, J. T. M. de Jong, D. C. E. Bakker, B. M. Löscher, C. Veth, U. Bathmann, V. Smetacek, Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern Ocean Nature 1995, 373, 412.
| Importance of iron for plankton blooms and carbon dioxide drawdown in the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXjsFCjs7w%3D&md5=3f1675f48a01eb97be2ac62b3be3feffCAS |
[3] K. S. Johnson, R. M. Gordon, K. H. Coale, What controls dissolved iron concentrations in the world ocean? Mar. Chem. 1997, 57, 137.
| What controls dissolved iron concentrations in the world ocean?Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXks12msbg%3D&md5=a96aadd612e3dfeccd8367410deda1cbCAS |
[4] M. C. Nielsdóttir, C. M. Moore, R. Sanders, D. J. Hinz, E. P. Achterberg, Iron limitation of the postbloom phytoplankton communities in the Iceland Basin Global Biogeochem. Cycles 2009, 23, GB3001.
| Iron limitation of the postbloom phytoplankton communities in the Iceland BasinCrossref | GoogleScholarGoogle Scholar |
[5] C. M. Moore, M. M. Mills, E. P. Achterberg, R. J. Geider, J. LaRoche, M. I. Lucas, M. L. McDonagh, X. Pan, A. J. Poulton, M. J. A. Rijkenberg, D. J. Suggett, S. J. Ussher, E. M. S. Woodward, Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability Nat. Geosci. 2009, 2, 867.
| Large-scale distribution of Atlantic nitrogen fixation controlled by iron availabilityCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhsVyqsbrL&md5=83c45d2ee26ad850725866d1f3e9fe17CAS |
[6] M. Gledhill, C. M. G. van den Berg, Determination of complexation of iron(III) with natural organic complexing ligands in seawater using cathodic stripping voltammetry Mar. Chem. 1994, 47, 41.
| Determination of complexation of iron(III) with natural organic complexing ligands in seawater using cathodic stripping voltammetryCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2cXmtFansbc%3D&md5=657fe2c9f36df81d37cf7624a1f9828aCAS |
[7] M. J. A. Rijkenberg, C. F. Powell, M. Dall’Osto, M. C. Nielsdottir, M. D. Patey, P. G. Hill, A. R. Baker, T. D. Jickells, R. M. Harrison, E. P. Achterberg, Changes in iron speciation following a Saharan dust event in the tropical North Atlantic Ocean Mar. Chem. 2008, 110, 56.
| Changes in iron speciation following a Saharan dust event in the tropical North Atlantic OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXls1KqtrY%3D&md5=efde93abb88d7a3aa6db54c2ccd9d478CAS |
[8] L. J. A. Gerringa, A.-C. Alderkamp, P. Laan, C.-E. Thuróczy, H. J. W. de Baar, M. M. Mills, G. L. van Dijken, H. van Haren, K. R. Arrigo, Iron from melting glaciers fuels the phytoplankton blooms in Amundsen Sea (Southern Ocean); iron biogeochemistry Deep Sea Res. Part II Top. Stud. Oceanogr. 2012, 71–76, 16.
| Iron from melting glaciers fuels the phytoplankton blooms in Amundsen Sea (Southern Ocean); iron biogeochemistryCrossref | GoogleScholarGoogle Scholar |
[9] C.-E. Thuróczy, A.-C. Alderkamp, P. Laan, L. J. A. Gerringa, H. J. W. de Baar, K. R. Arrigo, Key role of organic complexation of iron in sustaining phytoplankton blooms in the Pine Island and Amundsen Polynyas (Southern Ocean) Deep Sea Res. Part II Top. Stud. Oceanogr. 2012, 71–76, 49.
| Key role of organic complexation of iron in sustaining phytoplankton blooms in the Pine Island and Amundsen Polynyas (Southern Ocean)Crossref | GoogleScholarGoogle Scholar |
[10] S. A. Bennett, E. P. Achterberg, D. P. Connelly, P. J. Statham, G. R. Fones, C. R. German, The distribution and stabilisation of dissolved Fe in deep-sea hydrothermal plumes Earth Planet. Sci. Lett. 2008, 270, 157.
| The distribution and stabilisation of dissolved Fe in deep-sea hydrothermal plumesCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXmvVOmtLY%3D&md5=4e8c88060f10fff9361aa3df06f06c30CAS |
[11] M. B. Klunder, P. Laan, R. Middag, H. J. W. de Baar, K. Bakker, Dissolved iron in the Arctic Ocean: important role of hydrothermal sources, shelf input and scavenging removal J. Geophys. Res. – Oceans 2012, 117, C04014.
| Dissolved iron in the Arctic Ocean: important role of hydrothermal sources, shelf input and scavenging removalCrossref | GoogleScholarGoogle Scholar |
[12] C. S. Hassler, V. Schoemann, Bioavailability of organically bound Fe to model phytoplankton of the Southern Ocean Biogeosciences 2009, 6, 2281.
| Bioavailability of organically bound Fe to model phytoplankton of the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXltVCqsg%3D%3D&md5=0239f68561f6d9da5332dcd10ac65205CAS |
[13] M. T. Maldonado, N. M. Price, Utilization of iron bound to strong organic ligands by plankton communities in the subarctic Pacific Ocean Deep Sea Res. Part II Top. Stud. Oceanogr. 1999, 46, 2447.
| Utilization of iron bound to strong organic ligands by plankton communities in the subarctic Pacific OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1MXnsVCqt74%3D&md5=1cf33a9c2d1ae38118c22cbcf74412e7CAS |
[14] M. J. A. Rijkenberg, L. J. A. Gerringa, V. E. Carolus, I. Velzeboer, H. J. W. de Baar, Enhancement and inhibition of iron photoreduction by individual ligands in open ocean seawater Geochim. Cosmochim. Acta 2006, 70, 2790.
| Enhancement and inhibition of iron photoreduction by individual ligands in open ocean seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XksFyrsLo%3D&md5=d34d4cad240f1548e590e9f4b5892a34CAS |
[15] R. J. M. Hudson, Which aqueous species control the rates of trace metal uptake by aquatic biota? Observations and predictions of non-equilibrium effects Sci. Total Environ. 1998, 219, 95.
| Which aqueous species control the rates of trace metal uptake by aquatic biota? Observations and predictions of non-equilibrium effectsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXlslWltrw%3D&md5=15b3421dda9c965b1fab3e25ccdce913CAS |
[16] Y. Shaked, A. B. Kustka, F. M. M. Morel, A general kinetic model for iron acquisition by eukaryotic phytoplankton Limnol. Oceanogr. 2005, 50, 872.
| A general kinetic model for iron acquisition by eukaryotic phytoplanktonCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlt1ChsLk%3D&md5=bedf80827f0eb472a792f79a1038a168CAS |
[17] T. P. Salmon, L. Andrew, A. L. Rose, B. A. Neilan, T. D. Waite, The FeL model of iron acquisition: non-dissociative reduction of ferric complexes in the marine environment Limnol. Oceanogr. 2006, 51, 1744.
| The FeL model of iron acquisition: non-dissociative reduction of ferric complexes in the marine environmentCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xot1antbo%3D&md5=8974e114b057f2cd0c118a834d7698ffCAS |
[18] J. Buffle, G. G. Leppard, Characterization of aquatic colloids and macromolecules. 1 Structure and characterization of aquatic colloids Environ. Sci. Technol. 1995, 29, 2169.
| Characterization of aquatic colloids and macromolecules. 1 Structure and characterization of aquatic colloidsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXntFKksrs%3D&md5=1ad0a10d15bf6de9a399777fddbb1378CAS | 22280252PubMed |
[19] J. Buffle, G. G. Leppard, Characterization of aquatic colloids and macromolecules. 2. Key role of physical structures on analytical results Environ. Sci. Technol. 1995, 29, 2176.
| Characterization of aquatic colloids and macromolecules. 2. Key role of physical structures on analytical resultsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXntFKksrg%3D&md5=2fc454f0873cd316955a1bb861a01f91CAS | 22280253PubMed |
[20] H. M. Macrellis, C. G. Trick, E. L. Rue, G. Smith, K. W. Bruland, Collection and detection of natural iron-binding ligands from seawater Mar. Chem. 2001, 76, 175.
| Collection and detection of natural iron-binding ligands from seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXnslSms74%3D&md5=74a45f82d491befd716ecb10b537883eCAS |
[21] E. Mawji, M. Gledhill, J. A. Milton, G. A. Tarran, S. Ussher, A. Thompson, G. A. Wolff, P. J. Worsfold, E. P. Achterberg, Hydroxamate siderophores: occurrence and importance in the Atlantic Ocean Environ. Sci. Technol. 2008, 42, 8675.
| Hydroxamate siderophores: occurrence and importance in the Atlantic OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhtlWqurzI&md5=e644b31df3c31400d24a182f5bbd5314CAS | 19192780PubMed |
[22] E. Mawji, M. Gledhill, J. A. Milton, M. V. Zubkov, A. Thompson, G. A. Wolff, E. P. Achterberg, Production of siderophore type chelates in Atlantic Ocean waters enriched with different carbon and nitrogen sources Mar. Chem. 2011, 124, 90.
| Production of siderophore type chelates in Atlantic Ocean waters enriched with different carbon and nitrogen sourcesCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXksVCgtbg%3D&md5=f18e34c6b12270a98d72b9b8f9c019caCAS |
[23] L. M. Laglera, C. M. G. van den Berg, Evidence for geochemical control of iron by humic substances in seawater Limnol. Oceanogr. 2009, 54, 610.
| Evidence for geochemical control of iron by humic substances in seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXhsVCrtrrP&md5=99395040952acc6d3c6053b6a68142fbCAS |
[24] L. M. Laglera, G. Battaglia, C. M. G. van den Berg, Effect of humic substances on the iron speciation in natural waters by CLE/CSV Mar. Chem. 2011, 127, 134.
| Effect of humic substances on the iron speciation in natural waters by CLE/CSVCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhsVyksb3F&md5=b462c021c8628fce3b6ea56c14dcad12CAS |
[25] C. S. Hassler, V. Schoemann, C. Mancuso Nichols, E. C. V. Butler, P. W. Boyd, Saccharides enhance iron bioavailability to Southern Ocean phytoplankton Proc. Natl. Acad. Sci. USA 2011, 108, 1076.
| Saccharides enhance iron bioavailability to Southern Ocean phytoplanktonCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXhtlWrs7c%3D&md5=c93ac5f299959077daea2b90ed7fa02dCAS | 21169217PubMed |
[26] E. L. Rue, K. W. Bruland, Complexation of iron(III) by natural organic ligands in the central north Pacific as determined by a new competitive ligand equilibration/absorptive cathodic stripping voltammetric method Mar. Chem. 1995, 50, 117.
| Complexation of iron(III) by natural organic ligands in the central north Pacific as determined by a new competitive ligand equilibration/absorptive cathodic stripping voltammetric methodCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXotVaqu74%3D&md5=a8f89901edd4c7cc1d6bbfd4a2ec2449CAS |
[27] P. L. Croot, M. Johansson, Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-p-cresol (TAC) Electroanalysis 2000, 12, 565.
| Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-p-cresol (TAC)Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXjs12hurw%3D&md5=3c94bfceeeb5de9659c8d2d5ab1fca56CAS |
[28] C. M. G. van den Berg, Chemical speciation of iron in seawater by cathodic stripping voltammetry with dihydroxynaphthalene Anal. Chem. 2006, 78, 156.
| Chemical speciation of iron in seawater by cathodic stripping voltammetry with dihydroxynaphthaleneCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXht1KjsbvN&md5=63cc1270d1ede351bc33193dd0324becCAS |
[29] I. Langmuir, The constitution and fundamental properties of solids and liquids, part 1: solids J. Am. Chem. Soc. 1916, 38, 2221.
| The constitution and fundamental properties of solids and liquids, part 1: solidsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaC28Xhs1egsQ%3D%3D&md5=235454b25895022671b61d8290370047CAS |
[30] C. M. G. van den Berg, Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO, I. Theory Mar. Chem. 1982, 11, 307.
| Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO, I. TheoryCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL38XlsFShsbc%3D&md5=7b55329a8171d566b8d65defa535a862CAS |
[31] I. Ružić, Theoretical aspects of the direct titration of natural waters and its information yield for trace metal speciation Anal. Chim. Acta 1982, 140, 99.
| Theoretical aspects of the direct titration of natural waters and its information yield for trace metal speciationCrossref | GoogleScholarGoogle Scholar |
[32] M. Cheize, G. Sarthou, P. L. Croot, E. Bucciarelli, A.-C. Baudoux, A. R. Baker, Iron organic speciation determination in rainwater using cathodic stripping voltammetry Anal. Chim. Acta 2012, 736, 45.
| Iron organic speciation determination in rainwater using cathodic stripping voltammetryCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38XoslSltrk%3D&md5=f25f8e5ffcfb5d67b963c7a2389037ceCAS | 22769004PubMed |
[33] G. Scatchard, The attractions of proteins for small molecules and ions Ann. N. Y. Acad. Sci. 1949, 51, 660.
| The attractions of proteins for small molecules and ionsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaH1MXktFGktw%3D%3D&md5=933a5e3e938fb9474ba0ba20ea4d8183CAS |
[34] L. J. A. Gerringa, P. M. J. Herman, T. C. W. Poortvliet, Comparison of the linear Van den Berg–Ružić transformation and the non-linear fit of the Langmuir isotherm applied to Cu speciation data in the estuarine environment Mar. Chem. 1995, 48, 131.
| Comparison of the linear Van den Berg–Ružić transformation and the non-linear fit of the Langmuir isotherm applied to Cu speciation data in the estuarine environmentCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXivFygu7g%3D&md5=c0f476121a767fd325cc51b970f69e2dCAS |
[35] R. J. M. Hudson, E. L. Rue, K. W. Bruland, Modeling complexometric titrations of natural water samples Environ. Sci. Technol. 2003, 37, 1553.
| Modeling complexometric titrations of natural water samplesCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3sXitVOlsbk%3D&md5=6a651be522c3e2527b8de56e0e2711e4CAS |
[36] N. J. Turoczy, J. E. Sherwood, Modification of the van den Berg–Ruzic method for the investigation of complexation parameters of natural waters Anal. Chim. Acta 1997, 354, 15.
| Modification of the van den Berg–Ruzic method for the investigation of complexation parameters of natural watersCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXnvVShu74%3D&md5=ca88c151af6937db9f6eb825ce3554ccCAS |
[37] J. Wu, M. Jin, Competitive ligand exchange voltammetric determination of iron organic complexation in seawater in two-ligand case: examination of accuracy using computer simulation and elimination of artifacts using iterative non-linear multiple regression Mar. Chem. 2009, 114, 1.
| Competitive ligand exchange voltammetric determination of iron organic complexation in seawater in two-ligand case: examination of accuracy using computer simulation and elimination of artifacts using iterative non-linear multiple regressionCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXmsFOnsrY%3D&md5=201e21ec2650fac0649bbf20e788f732CAS |
[38] E. Ibisanmi, S. G. Sander, P. W. Boyd, A. R. Bowie, K. A. Hunter, Vertical distributions of iron(III) complexing ligands in the Southern Ocean Deep Sea Res. Part II Top. Stud. Oceanogr. 2011, 58, 2113.
| Vertical distributions of iron(III) complexing ligands in the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXht1WksbnE&md5=cc91df761b3d4afc9900c79a432ee638CAS |
[39] S. G. Sander, K. A. Hunter, H. Harms, M. Wells, Numerical approach to speciation and estimation of parameters used in modeling trace metal bioavailability Environ. Sci. Technol. 2011, 45, 6388.
| Numerical approach to speciation and estimation of parameters used in modeling trace metal bioavailabilityCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3MXovFCntb8%3D&md5=ad430edabcc4f986efdd6e7431a1a68cCAS | 21751821PubMed |
[40] M. Gledhill, K. N. Buck, The organic complexation of iron in the marine environment: a review Front. Microbiol. 2012, 3, 69.
| The organic complexation of iron in the marine environment: a reviewCrossref | GoogleScholarGoogle Scholar | 22403574PubMed |
[41] A. Tagliabue, L. Bopp, O. Aumont, K. R. Arrigo, Influence of light and temperature on the marine iron cycle: from theoretical to global modelling Global Biogeochem. Cycles 2009, 23, GB2017.
| Influence of light and temperature on the marine iron cycle: from theoretical to global modellingCrossref | GoogleScholarGoogle Scholar |
[42] Y. Ye, C. Völker, D. A. Wolf-Gladrow, A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory site Biogeosciences 2009, 6, 2041.
| A model of Fe speciation and biogeochemistry at the Tropical Eastern North Atlantic Time-Series Observatory siteCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXltVCktQ%3D%3D&md5=a47642d1601eb2367d663686f1be8c12CAS |
[43] C.-E. Thuróczy, L. J. A. Gerringa, M. Klunder, P. Laan, H. J. W. de Baar, Organic complexation of dissolved iron in the Atlantic sector of the Southern Ocean Deep Sea Res. Part II Top. Stud. Oceanogr. 2011, 58, 2695.
| Organic complexation of dissolved iron in the Atlantic sector of the Southern OceanCrossref | GoogleScholarGoogle Scholar |
[44] C.-E. Thuróczy, L. J. A. Gerringa, M. P. Klunder, P. Laan, M. Le Guitton, H. J. W. de Baar, Distinct trends in the speciation of iron between the shelf seas and the deep basins of the Arctic Ocean J. Geophys. Res. 2011, 116, C10009.
| Distinct trends in the speciation of iron between the shelf seas and the deep basins of the Arctic OceanCrossref | GoogleScholarGoogle Scholar |
[45] S. C. Apte, M. J. Gardner, J. E. Ravenscroft, An evaluation of voltammetric titration procedures for the determination of trace metal complexation in natural waters by use of computer simulation Anal. Chim. Acta 1988, 212, 1.
| An evaluation of voltammetric titration procedures for the determination of trace metal complexation in natural waters by use of computer simulationCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1cXlvFKltbw%3D&md5=7e4b9b21453c40022517989d61b74758CAS |
[46] C. M. G. van den Berg, M. Nimmo, P. Daly, D. R. Turner, Effects of the detection window on the determination of organic copper speciation in estuarine waters Anal. Chim. Acta 1990, 232, 149.
| Effects of the detection window on the determination of organic copper speciation in estuarine watersCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3cXkt12js7c%3D&md5=98d42b28b8b3f59e92c6cd66f72f63c6CAS |
[47] J. F. Wu, G. W. Luther, Complexation of FeIII by natural organic-ligands in the northwest Atlantic Ocean by a competitive ligand equilibration method and a kinetic approach Mar. Chem. 1995, 50, 159.
| Complexation of FeIII by natural organic-ligands in the northwest Atlantic Ocean by a competitive ligand equilibration method and a kinetic approachCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2MXotVaqu7w%3D&md5=9354da47cbb61e7370295e0e8abbd10eCAS |
[48] A. E. Witter, D. A. Hutchins, A. Butler, G. W. Luther, Determination of conditional stability constants and kinetic constants for strong model Fe-binding ligands in seawater Mar. Chem. 2000, 69, 1.
| Determination of conditional stability constants and kinetic constants for strong model Fe-binding ligands in seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXhvVCktbw%3D&md5=02e4c29260f23162e1c109d0676bcce2CAS |
[50] M. Boye, C. M. G. van den Berg, J. T. M. de Jong, H. Leach, P. L. Croot, H. J. W. de Baar, Organic complexation of iron in the Southern Ocean Deep Sea Res. Part I Oceanogr. Res. Pap. 2001, 48, 1477.
| Organic complexation of iron in the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXis1Oitrs%3D&md5=70d9e5cde2f51a32afb7a9b6a590ef65CAS |
[49] P. L. Croot, K. Andersson, M. Öztürk, D. R. Turner, The distribution and speciation of iron along 61°E in the Southern Ocean Deep Sea Res. Part II Top. Stud. Oceanogr. 2004, 51, 2857.
| The distribution and speciation of iron along 61°E in the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXhtVChu7zK&md5=fe1fea178223eb055c0724ee3adead21CAS |
[51] M. Boye, J. Nishioka, P. L. Croot, P. Laan, K. R. Timmermans, H. J. W. de Baar, Major deviations of iron complexation during 22 days of a mesoscale iron enrichment in the open Southern Ocean Mar. Chem. 2005, 96, 257.
| Major deviations of iron complexation during 22 days of a mesoscale iron enrichment in the open Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXmvFGjtL8%3D&md5=6e1b6dadbf42f2915ac0a5a1727679d1CAS |
[52] L. J. A. Gerringa, M. J. W. Veldhuis, K. R. Timmermans, G. Sarthou, H. J. W. de Baar, Co-variance of dissolved Fe-binding ligands with biological observations in the Canary Basin Mar. Chem. 2006, 102, 276.
| Co-variance of dissolved Fe-binding ligands with biological observations in the Canary BasinCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XhtVWrt7nI&md5=365d97e27b4c8aa4c58babeab17965b0CAS |
[53] J. T. Cullen, B. A. Bergquist, J. W. Moffett, Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic Ocean Mar. Chem. 2006, 98, 295.
| Thermodynamic characterization of the partitioning of iron between soluble and colloidal species in the Atlantic OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28XjsF2ltg%3D%3D&md5=f26dd0e66379157192d79e83cac146e7CAS |
[54] K. N. Buck, M. C. Lohan, C. J. M. Berger, K. W. Bruland, Dissolved iron speciation in two distinct river plumes and an estuary: implications for riverine iron supply Limnol. Oceanogr. 2007, 52, 843.
| Dissolved iron speciation in two distinct river plumes and an estuary: implications for riverine iron supplyCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXkt1Wgs7Y%3D&md5=0f55f933998a06da900adbeb216c2dd0CAS |
[55] C.-E. Thuróczy, L. J. A. Gerringa, M. Klunder, R. Middag, P. Laan, K. R. Timmermans, H. J. W. de Baar, Speciation of Fe in the north east Atlantic Ocean Deep Sea Res. Part I Oceanogr. Res. Pap. 2010, 57, 1444.
| Speciation of Fe in the north east Atlantic OceanCrossref | GoogleScholarGoogle Scholar |
[56] K. N. Buck, J. Moffett, K. A. Barbeau, R. M. Bundy, Y. Kondo, J. Wu, The organic complexation of iron and copper: an intercomparison of competitive ligand exchange–adsorptive cathodic stripping voltammetry (CLE-ACSV) techniques Limnol. Oceanogr. Methods 2012, 10, 496.
| 1:CAS:528:DC%2BC38XhtlyntrbE&md5=270edffe026d67e4a6212d6c8d9e1f49CAS |
[57] X. Liu, F. J. Millero, The solubility of iron in seawater Mar. Chem. 2002, 77, 43.
| The solubility of iron in seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXptFemt7c%3D&md5=a5e7c62e5b446e60a8db3d83709f990dCAS |
[58] L. A. Miller, K. W. Bruland, Competitive equilibration techniques for determining transition metal speciation in natural waters: evaluation using model data Anal. Chim. Acta 1997, 343, 161.
| Competitive equilibration techniques for determining transition metal speciation in natural waters: evaluation using model dataCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXis1Wmsr0%3D&md5=b985e67fc1c07376ae9d7a2204089c7fCAS |
[59] G. L. Atkins, I. A. Nimmo, A comparison of seven methods for fitting the Michaelis–Menten equation Biochem. J. 1975, 149, 775.
| 1:CAS:528:DyaE2MXlslCkt78%3D&md5=b56121395845f9ba0536995a0e6746b7CAS | 1201002PubMed |
[60] A. C. Fischer, J. J. Kroon, T. G. Verburg, T. Teunissen, H. T. Wolterbeek, On the relevance of iron adsorption to container materials in small-volume experiments on iron marine chemistry: 55Fe-aided assessment of capacity, affinity and kinetics Mar. Chem. 2007, 107, 533.
| On the relevance of iron adsorption to container materials in small-volume experiments on iron marine chemistry: 55Fe-aided assessment of capacity, affinity and kineticsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXhsVSisL7O&md5=d43303cf56ec05e540df617115a999fdCAS |
[61] J. N. Fitzsimmons, E. A. Boyle, An intercalibration between the GEOTRACES GO-FLO and the MITESS/Vanes sampling systems for dissolved iron concentration analyses (and a closer look at adsorption effects) Limnol. Oceanogr. Methods 2012, 10, 437.
| 1:CAS:528:DC%2BC38XhtlyntrnJ&md5=928730508632deb3c077402f05de0a6cCAS |
[62] R. M. Town, H. P. van Leeuwen, Measuring marine iron(III) complexes by CLE-AdSV Environ. Chem. 2005, 2, 80.
| Measuring marine iron(III) complexes by CLE-AdSVCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlvVChs7g%3D&md5=ead42ff82809e091681336085f85135dCAS |
[63] K. A. Hunter, Comment on ‘Measuring marine iron(III) complexes by CLE-AdSV’ Environ. Chem. 2005, 2, 85.
| Comment on ‘Measuring marine iron(III) complexes by CLE-AdSV’Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlvVChs74%3D&md5=42a29954613aaed846ef9e90c207d7b7CAS |
[64] C. M. G. van den Berg, Organic iron complexation is real, the theory is used incorrectly; comment on ‘Measuring marine iron(III) complexes by CLE-AdSV’ Environ. Chem. 2005, 2, 88.
| Organic iron complexation is real, the theory is used incorrectly; comment on ‘Measuring marine iron(III) complexes by CLE-AdSV’Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlvVChs78%3D&md5=ab009d70544395da42e333f91869f58aCAS |
[65] R. M. Town, H. P. van Leeuwen, Reply to comments on ‘Measuring marine iron(III) complexes by CLE-AdSV’ Environ. Chem. 2005, 2, 90.
| Reply to comments on ‘Measuring marine iron(III) complexes by CLE-AdSV’Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2MXlvVChsrc%3D&md5=380d14ece2c1d2708c9950ac90c7e330CAS |
[66] P. L. Croot, M. I. Heller, The importance of kinetics and redox in the biogeochemical cycling of iron in the surface ocean Front. Microbiol. 2012, 3, 219.
| The importance of kinetics and redox in the biogeochemical cycling of iron in the surface oceanCrossref | GoogleScholarGoogle Scholar | 22723797PubMed |
[67] J. Buffle, Complexation Reactions in Aquatic Systems – An Analytical Approach, 1988, pp. 165–303 (Ellis Horwood Limited: Chichester, UK).
[68] R. S. Altmann, J. Buffle, The use of differential equilibrium functions for interpretation of metal binding in complex ligand systems: its relation to site occupation and site affinity distributions Geochim. Cosmochim. Acta 1988, 52, 1505.
| The use of differential equilibrium functions for interpretation of metal binding in complex ligand systems: its relation to site occupation and site affinity distributionsCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaL1cXltFOis7w%3D&md5=58b1193f6b0dabe7153078cdc35ff8e7CAS |
[69] R. Yang, C. M. G. van den Berg, Metal complexation by humic substances in seawater Environ. Sci. Technol. 2009, 43, 7192.
| Metal complexation by humic substances in seawaterCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1MXmvFOisr8%3D&md5=0a721e2f2401151b6784779d7735ac70CAS | 19848121PubMed |
[70] M. B. Kogut, B. M. Voelker, Kinetically inert Cu in coastal waters Environ. Sci. Technol. 2003, 37, 509.
| Kinetically inert Cu in coastal watersCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD38Xps1Wqt7Y%3D&md5=676f7df8f1c37c79278478d4039e5cc5CAS | 12630466PubMed |
[71] R. F. Nolting, L. J. A. Gerringa, M. J. W. Swagerman, K. R. Timmermans, H. J. W. de Baar, FeIII speciation in the high nutrient, low chlorophyll Pacific region of the Southern Ocean Mar. Chem. 1998, 62, 335.
| FeIII speciation in the high nutrient, low chlorophyll Pacific region of the Southern OceanCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXlt1ajsLg%3D&md5=b3c769ac89b8063619c9466b74065b2aCAS |
[72] L. Wilkinson, M. Hill, J. P. Welna, G. K. Birkenbeuel, SYSTAT for Windows: Statistics, Ver. 5 1992 (SYSTAT: Evanston, IL).
[73] L. M. Laglera, J. Downes, J. Santos-Echeandia, Comparison and combined use of linear and non-linear fitting for the estimation of complexing parameters from metal titrations of estuarine samples by CLE/AdCSV Mar. Chem. 2013, 155, 102.
| Comparison and combined use of linear and non-linear fitting for the estimation of complexing parameters from metal titrations of estuarine samples by CLE/AdCSVCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3sXhtlCnsLfL&md5=638ae157873b82f24e8b3a0651cd67f8CAS |
[74] K. N. Buck, K. W. Bruland, The physicochemical speciation of dissolved iron in the Bering Sea, Alaska Limnol. Oceanogr. 2007, 52, 1800.
| The physicochemical speciation of dissolved iron in the Bering Sea, AlaskaCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXht1ahsLzF&md5=77cab365fddce8d47e979546aff25cf5CAS |
[75] W. H. Press, B. P. Flannery, S. A. Teukolsky, W. T. Vetterling, root finding and nonlinear sets of equations, in Numerical Recipes, 1986, pp. 347–393 (Cambridge University Press: Cambridge, UK).
[76] E. L. Rue, K. W. Bruland, 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. 1997, 42, 901.
| The role of organic complexation on ambient iron chemistry in the equatorial Pacific Ocean and the response of a mesoscale iron addition experimentCrossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK1cXjsFCm&md5=c303bbd389654c6c79f3a5d4fa3e7df1CAS |
