PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Equatorial Zonal Sections of Al, Fe and MnSlide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Lecture 15 – Iron Ocean ChemistrySee:Johnson, Gordon and Coale (1997)What controls dissolved iron concentrations in the world ocean?Marine Chemistry, 57, 137-161Iron DistributionsIron Speciation and SolubilityBiological componentBiochemistry and PhysiologyChemical component Concentrations of and exchange between different Fe species Ecological/Physical/Geochemical componentEcosystem structure, Fe and C inputs, exports, and internal cyclingThe Biogeochemical Cycle of Iron in SeawaterVertical Profiles of Selected Metals in the North Pacific Ocean(from Butler (1998) Science, 281, 207)All Fe data as of 1997 (Johnson et al, 1997)coastalWhat are key features?Dissolved Fe model (Johnson et al 1997)Vertical flux of POC FC = F100 (Z/100)-bQ = Fe/CRemineralization Flux PFe = Q FC/Z = (b/100-b) QF100 Z-(1+b) = 45 Q F100 Z-1.858Scavenging sink = RFe = kFe [(Fe) – (Fe)solubility]where Fesolubility = 0.6 nmol kg-1Fe/t = 45 Q F100 Z-1.858 - kFe [(Fe) – (Fe)soly] + KZ 2Fe/Z2remineralization scavenging mixingDissolved Iron (nmol kg-1)0.0 0.2 0.4 0.6Depth (m)0100200300400FeLine 90JGOFS 3/92JGOFS 4/92JGOFS 10/92Dissolved Iron (nmol kg-1)0.0 0.2 0.4 0.6Depth (m)0100200300400MBARIRue & BrulandWu et alEqPac - 140W, 0N HOT Stn ALOHAFe at EqPac and HOT –different years; different methodsAverage Surface Ocean NitrateHNLC : High Nitrate Low Chlorophyll Due to Fe limitation??Dust Transport from continentsNorth Atlantic dust storm from the SaharaAerosol optical depthFe flux from dust to the ocean (Duce and Tindale, 1991)EqPac results (1992)Meridional section acrossequator at 140°W.Is there an Fe maximumin the EUC???What is the EUC??Fe dissolvedFe particulateCruise Track – EUCFe on the R/V Kilo Moana 2006Equatorial Undercurrent during Kilo 0625ADCP From P. Dutrieux(Hawaii)ө(EUC) =25.0 to 25.5Origin of theEquatorialUndercurrent(EUC)Equatorial Zonal Sections of Al, Fe and MnnMSpeciation is important!What constitutes “bioavailable” iron in seawater? soluble species colloids particulates1nm 10nm 0.1m 1m 10m 100mFe(III)' - Fe(OH)2+ Fe(OH)30 Fe(OH)4-Fe(II)' - Fe2+ FeCO30NOCO(CH2)2CONH(CH2)5CO(CH2)2CONH(CH2)5NOCOCH3NO(H2C)5H2NFeIIIFeNNNNCOO-COO-Fe(III)HOHOOHOHFe(III)OH2+OHiron oxide mineralorganic detritusInorganic speciation of iron – hydrolysis reactionsHydrolysis ReactionsFe3+ + H2O = FeOH2+ + H+log *K1 = -2.2FeOH2+ + H2O = Fe(OH)2+ + H+log *K2 = -3.4 or log *2 = -5.6 Fe(OH)2+ + H2O = Fe(OH)3º + H+log *K3 = -6.8Fe(OH)3º + H2O = Fe(OH)4- + H+log *K4 = -9.1Metals are acidsFor a homogeneous system: FeT = [Fe3+] + [FeOH2+] + [Fe(OH)2+] + [Fe(OH)3º] + [Fe(OH)4-]Heterogeneous System – Mass Balance with Iron SolubilityMass balance:FeT = [Fe3+] + [FeOH2+] + [Fe(OH)2+] + [Fe(OH)3º] + [Fe(OH)4-]FeT = [Fe3+] + [Fe3+] *K1/H+ + [Fe3+] *2/(H+)2 + [Fe3+] *2 / (H+)3 + [Fe3+] *4 / (H+)4FeT = [Fe3+] { 1 + *K1/H + *2/H2 + *3/H3 + *4/H4 }Fe3+ = Fe3+ / FeTSolubility product of iron oxide is written as:Fe(OH)3am = Fe 3+ + 3 OH-3 OH- + 3 H+ = 3 H2OorFe(OH)3am + 3H+ = Fe3+ + 3 H2O*KSO = 103.2 = [Fe3+] / (H+)3Then: FeT = (*KSO (H)3 ) { 1 + *K1/H + *2/H2 + *3/H3 + *4/H4 }Example:What is the solubility of Fe(OH)3(s) in terms of the uncharged dissolved species, Fe(OH)3º?Add two reactions:Fe(OH)3(s) + 3H+ = Fe3+ + 3 H2O log K = 3.2Fe3+ + 3H2O = Fe(OH)3º + 3H+ log K = -12.4-------------------------------------------------------------------Fe(OH)3 (s) = Fe(OH)3º log K = -9.2K = Fe(OH)3º / Fe(OH)3(s) ≈ Fe(OH)3º0Dissolved Fe = Fe(OH)3º = 10-9.2 MSolubility diagram for iron oxideFe in deep seawater= 0.7 x 10-9M= 10-9.15Solubility minimum at pH 8Other inorganic species of ironOrganic Ligands(see Rue and Bruland, 1995)Organic Ligand ReactionsFe3+ + Ln- = FeL K = [FeL] / [Fe3+] [Ln-] = 1026.5 for DesferolThe ligands (L) can be made by (an iron chelating siderophore)both bacteria and plankton so: FeL = K [Fe3+] [Ln-]Then:FeT = Fe’ + FeL (inorganic species) (organic species) FeT = [Fe3+] { 1 + *K1/H + *2/H2 + *3/H3 + *4/H4 + KFeL [L]}Example assuming a ligand concentration Ln- = 0.44nM = 10-9.35M and pH = 8FeT = [Fe3+] ( 1 + 105.8 + 1010.3 + 1011.5 + 1010.4 + 1017.5)Then: Fe’ = 0.0039%FeL = 99.996%Rue and Bruland (1995) analyzed natural seawater and foundFe’ = 0.03%FeL = 99.97%In surface SW most Fe is chelated!Much of dissolved iron is colloidal (from Wu et al (2001) Science, 293, 847)Concentration of soluble (<0.02m) ligands in the eastern North Atlantic.(Wu et al (2001) Science 293, 847)Metallenzymes containingIron and other transition Metals. From Butler (1998)Science, 281, 207.Fe redox/photo chemistryFe – redox/photo chemistrySpeciation of Major Ions in SeawaterExample CalculationThe MgSO4° ion pairMgSO4° = Mg2+ + SO42- log K = -2.4 = 4 x 10-3K = (MgSO4°) / (Mg2+)(SO42-)MgT = Mg2+ + MgSO4° = 50 x 10-3 MSO4T = 28 x 10-3 MAnswer:11% of MgT is MgSO421.5% of SO4T is