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Sample collection and filtering: <\/strong>Water column samples were collected by the U.S. GEOTRACES sampling team from 24 modified 12 L Teflon-lined GoFlo samplers (General Oceanics) deployed on the GEOTRACES clean CTD rosette system. The U.S. GEOTRACES sampling team filtered the samples through 0.2 \u00b5m Supor Acropak filter cartridges (Pall) inside the U.S. GEOTRACES clean-air laboratory van. Near-surface samples (~2 m depth) were collected underway either on approach or leaving each station using the Ken Bruland lab towfish (\u201cGeoFish\u201d) deployed to collect surface samples from outside the wake of the ship. Seawater from the towfish was pumped directly into the Bruland lab clean air laboratory van and filtered through 0.2 \u00b5m Supor Acropak filter cartridges. Filtered seawater samples for Fe speciation (organic complexation) analyses were collected in 500 mL acid-cleaned Nalgene narrow-mouth fluorinated high-density polyethylene bottles that were conditioned with a Milli-Q fill for at least two weeks, and rinsed three times with filtered sample prior to sample collection. All filtered seawater samples for dissolved iron speciation from leg 1 were provided directly to the PI (Buck), who either analyzed the sample shipboard or froze the sample at -20 \u00baC for laboratory-based analyses post cruise.<\/p>\n Dissolved iron speciation (organic complexation) analyses: <\/strong>Dissolved Fe speciation (organic complexation) was analyzed using a competitive ligand exchange- adsorptive cathodic stripping voltammetry (CLE-ACSV) method with salicylaldoxime as the added competing ligand (Buck et al. 2007, 2010, 2012), modified from the original Rue and Bruland (1995) method. Dissolved Fe additions of 0 to 7.5 nM were used in the titrations, for a total of at least 10 points in each titration. Deposition times of 90 to 120 s were applied to the analyses. All analyses were performed on Bioanalytical Systems (BASi<\/em>) Controlled Growth Mercury Electrodes (static mercury drop setting, size 14) with Epsilon e2 (BASi<\/em>) electrochemical analyzers. There are no reference samples available for iron speciation\/ organic complexation measurements of iron in seawater, though this method was shown to compare well with other labs and techniques in the GEOTRACES intercalibration exercises (Buck et al. 2012, 2016).<\/p><\/div>","@type":"rdf:HTML"}],"http:\/\/ocean-data.org\/schema\/hasBriefDescription":[{"@value":"Profiles of concentrations of dissolved iron-binding ligands and their respective conditional stability constants","@language":"en-US"}],"http:\/\/purl.org\/dc\/terms\/description":[{"@value":" Concentrations of dissolved iron-binding ligands and their respective conditional stability constants in water column samples from full depth stations occupied during the first leg (KN199-4) of the U.S. GEOTRACES North Atlantic zonal transect cruises on the R\/V Knorr in 2010.<\/p>\n The FISH and BOTTLE data have been split into separate columns as per GEOTRACES Parameter Naming Conventions. The FISH data are to the far right.<\/p>\n Versions:<\/strong><\/p>\n version 6, 2016-12-08: separate columns for Fish and Bottle samples; quality flags added. Dissolved iron (DFe) concentrations determined by flow injection analysis (FIA) in Peter Sedwick\u2019s lab at Old Dominion University were used in the data interpretation to calculate ligand concentrations and conditional stability constants from the sample titrations. The DFe values used for this dataset are provided in the speciation submission for reference, please see Sedwick et al. (2015) for the complete dissolved iron data and methods.<\/p>\n Titration data was interpreted with a combination of Scatchard (Scatchard 1949) and van den Berg-Ruzic (Ruzic 1982; van den Berg 1982) linearization techniques, as has been described previously (Buck et al. 2012, 2015, 2016). An inorganic side reaction coefficient, aFe<\/sub>\u00a2<\/sub>, of 1010<\/sup> was used in the iron speciation calculations (Buck et al. 2012). Ligand concentrations and conditional stability constants determined from each linearization of a titration dataset were then combined for a final ligand concentration and conditional stability constant for each sample. When available, results from replicate titration analyses were averaged together and the average with standard deviations of all sample titrations were then reported for each parameter in the spreadsheet.<\/p>\n The detection limit for the electroactive Fe-SA complex has been found to be 0.01 nM (Buck et al. 2007), calculated as three times the standard deviation of measured peak height from a 0.05 nM Fe addition to UV-oxidized and chelexed seawater with a 900 s deposition time. For a 90 s deposition time, the detection limit for Fe-SA is ~0.1 nM. Two stations from the US GTNA cruises (2010-Stn5 and 2010-Stn 9) were analyzed in triplicate complete titrations, typically two conducted shipboard and one in the laboratory after storing frozen (-20 \u00baC). Over the full water column from both stations, the average standard deviation from the triplicate titrations of each sample was 0.11 nM (n = 36 samples, 108 titrations), and three times this standard deviation estimates a detection limit for ligand concentrations of 0.33 nM. For log K1<\/sub> values of this ligand class, from the same profiles, the average standard deviation was 0.15 (log units).<\/p>\n Related files and references:\u00a0 <\/strong><\/p>\n Buck, K. N., L. J. A. Gerringa, and M. J. A. Rijkenberg. 2016. An intercomparison of dissolved iron speciation at the Bermuda Atlantic Time-series Station (BATS): Results from the GEOTRACES Crossover Station A. Frontiers in Marine Biogeochemistry 3: article 262.<\/p>\n Buck, K. N., M. C. Lohan, C. J. M. Berger, and K. W. Bruland. 2007. Dissolved iron speciation in two distinct river plumes and an estuary: Implications for riverine iron supply. Limnology and Oceanography 52: 843-855.<\/p>\n Buck, K. N., K. E. Selph, and K. A. Barbeau. 2010. Iron-binding ligand production and copper speciation in an incubation experiment of Antarctic Peninsula shelf waters from the Bransfield Strait, Southern Ocean. Marine Chemistry 122: 148-159.<\/p>\n Buck, K. N., J. W. Moffett, K. A. Barbeau, R. M. Bundy, Y. Kondo, and J. Wu. 2012. The organic complexation of iron and copper: an intercomparison of competitive ligand exchange- adsorptive cathodic stripping voltammetry (CLE-ACSV) techniques. Limnology and Oceanography: Methods 10: 496-515.<\/p>\n Buck, K. N., B. Sohst, and P. N. Sedwick. 2015. The organic complexation of dissolved iron along the U.S. GEOTRACES (GA03) North Atlantic Section. Deep-Sea Research 116: 152-165.<\/p>\n Rue, E. L., and K. W. Bruland. 1995. 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. Marine Chemistry 50: 117-138.<\/p>\n Ru\u017ei\u0107, I. 1982. Theoretical aspects of the direct titration of natural waters and its information yield for trace metal speciation. Analytica Chimica Acta 140: 99-113.<\/p>\n Scatchard, G. 1949. The attractions of proteins for small molecules and ions. Annals of the New York Academy of Sciences 51: 660-672.<\/p>\n Sedwick, P. N., B. M. Sohst, S. J. Ussher, and A. R. Bowie. 2015. A zonal picture of the water column distribution of dissolved iron(II) during the U.S. GEOTRACES North Atlantic transect cruise (GEOTRACES GA03). Deep-Sea Research II 116: 166-175.<\/p>\n van den Berg, C. M. G. 1982. Determination of copper complexation with natural organic ligands in sea water by equilibrium with MnO2: I. Theory. Marine Chemistry 11: 307-322.<\/p>\n \u00a0<\/p>\n
\nversion 5, 19 Nov. 2014: Added L3 data.
\nversion 4, 14 April 2014: Revised values for KN204-1 measurements.
\nversion 3, 26 June 2013: KN199-04 station 7 values corrected.
\nversion 2, 10 June 2013: KN199-04 data updated, KN204-01 data added.
\nversion 1, 31 Dec. 2012: Initial data submitted.<\/p><\/div>","@type":"rdf:HTML"}],"http:\/\/www.w3.org\/2000\/01\/rdf-schema#label":[{"@value":"GT10-11 - Fe Speciation","@type":"xsd:string"}],"http:\/\/ocean-data.org\/schema\/hasProcessingDescription":[{"@value":"