Dataset: Dissolved iron speciation - CoFeMUG KN192-05

Name: Dissolved iron-binding ligands and their respective conditional stability constants in upper water column, R/V Knorr KN192-05, S. Atlantic subtropical gyre and Benguela upwelling region, Nov. 2007 (CoFeMUG project)
Published: 2016-12-02
Keywords: oceans

Cite This Dataset

Spatial Extent: N:-11.5 E:12.5 S:-25 W:-25

Project:

Cobalt, Iron and Micro-organisms from the Upwelling zone to the Gyre (GAc01) (CoFeMUG)

Program:

Ocean Carbon and Biogeochemistry (OCB)

U.S. GEOTRACES (U.S. GEOTRACES)

Principal Investigator:

Kristen Buck (Bermuda Institute of Ocean Sciences, BIOS)

BCO-DMO Data Manager:

Nancy Copley (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

Version Date:

2016-12-02

Restricted:

Validated:

Yes

Current State:

Final with updates expected

Dissolved iron-binding ligands and their respective conditional stability constants in upper water column, R/V Knorr KN192-05, S. Atlantic subtropical gyre and Benguela upwelling region, Nov. 2007 (CoFeMUG project)

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Description

Dissolved iron-binding organic ligand concentrations and conditional stability constants from CoFeMUG water column samples collected in 2007 in the Eastern South Atlantic on the R.V. Knorr, cruise KN192-05.

Samples were obtained through the CoFeMUG program, funded by NSF OCE-0452883 to Mak Saito (WHOI). Buck was funded for these analyses by the Walwyn Hughes Fund for Innovation at the Bermuda Institute of Ocean Sciences (BIOS).

These data should be considered and cited as preliminary until the public release of the GEOTRACES Intermediate Data Product in August 2017.

Methods & Sampling

Sampling and analytical methodology:

Sample collection and filtering: Water column samples were collected from a trace metal rosette outfitted with Teflon-coated X-Niskin samplers (Ocean Test Equipment) and deployed on a nonmetallic line. Samples were filtered through acid-cleaned 142-mm polycarbonate filters with a 0.4 µm pore size (Geotech Environmental) in a laminar flow clean hood. Please see Noble et al. (2012) for detailed information on sample acquisition and processing.

Filtered seawater samples for iron speciation (organic complexation) were collected in 500 mL acid-cleaned Nalgene narrow-mouth fluorinated high-density polyethylene (FPE) bottles that had been filled with Milli-Q for at least two weeks after acid cleaning and rinsed three times with filtered seawater prior to sample collection (Buck et al. 2012). All filtered seawater samples for dissolved iron speciation were frozen at -20 ºC shipboard by the sampling team and shipped to the Bermuda Institute of Ocean Sciences for laboratory-based analyses post cruise.

Dissolved iron speciation (organic complexation) analyses: 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, 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 12 points in each titration. Deposition times of 120 s were applied to the analyses. All analyses were performed on Bioanalytical Systems (BASi) Controlled Growth Mercury Electrodes (static mercury drop setting, size 14) with Epsilon e2 (BASi) 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).

FLAG: The standard Ocean Data View qualifying flags were used (reference all flags at https://www.bodc.ac.uk/data/codes_and_formats/odv_format/):

1: Good Value: Good quality data value that is not part of any identified malfunction and has been verified as consistent with real phenomena during the quality control process. [Used when data were shown to be reproducible]

2: Probably Good Value: Data value that is probably consistent with real phenomena but this is unconfirmed or data value forming part of a malfunction that is considered too small to affect the overall quality of the data object of which it is a part. [Used when the reported value reflects analysis of a single or unverified replicate]

3: Probably Bad Value: Data value recognized as unusual during quality control that forms part of a feature that is probably inconsistent with real phenomena. [Not used]

4: Bad Value: An obviously erroneous data value. [Not used]

5: Changed Value: Data value adjusted during quality control. [Not used]

6: Value Below Detection Limit: The level of the measured phenomenon was too small to be quantified by the technique employed to measure it. The accompanying value is the detection limit for the technique or zero if that value is unknown. [We report “not_detected” rather than zero or a detection limit value for this case]

7: Value in Excess: The level of the measured phenomenon was too large to be quantified by the technique employed to measure it. The accompanying value is the measurement limit for the technique. [Not used]

8: Interpolated Value: This value has been derived by interpolation from other values in the data object. [Not used]

9: Missing Value: The data value is missing. Any accompanying value will be a magic number representing absent data. [Not used]

Data Processing Description

Data processing:

Dissolved Fe concentrations for each sample from the Mak Saito lab at Woods Hole Oceanographic Institution were used to calculate ligand concentrations and conditional stability constants from the titrations; see Noble et al. (2012) for details of dissolved iron analyses. 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¢, of 1010 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.

Related files and references:

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.

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.

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.

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.

Noble, A. E., C. H. Lamborg, D. C. Ohnemus, P. J. Lam, T. J. Goepfert, C. I. Measures, C. H. Frame, K. L. Casciotti, G. R. Ditullio, J. Jennings, and M. A. Saito. 2012. Basin-scale inputs of cobalt, iron, and manganese from the Benguela-Angola front to the South Atlantic Ocean. Limnology and Oceanography 57: 989-1010.

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.

Ruzic, 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.

Scatchard, G. 1949. The attractions of proteins for small molecules and ions. Annals of the New York Academy of Sciences 51: 660-672.

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.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- column names reformatted to comply with BCO-DMO standards
- replaced blank cells with nd, 'no data'
- version 2016-12-05 replaced v2013-07-01: revised parameter names, added data columns for flags and ligand 3.

Data Files

File
Fe_speciation_v20161202.csv (Comma Separated Values (.csv), 6.95 KB) MD5:7062f6e79e27613316ffc03cbc2627c0 Primary data file for dataset ID 3986

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-0452883

Deployments

Deployment	Synonyms	Start Date	Platform	Investigator
KN192-05	GAc01 CoFeMUG KN192-5	2007-11-16	R/V Knorr	Mak A. Saito (Chief Scientist)	data info

Instruments

BASi Controlled Growth Mercury Electrode

Supplied Description:

http://www.basinc.com/products/ec/cgme.php

Instrument Type

Generic Name: BASi Controlled Growth Mercury Electrode

Acronym: BASI CGME

Generic Description:

Bioanalytical Systems (BASi) Mercury drop electrodes are generated by the BASi Controlled Growth Mercury Electrode (CGME) in three modes:

DME (Dropping Mercury Electrode) - mercury is allowed to flow freely from the reservoir down the capillary and so the growth of the mercury drop and its lifetime is controlled by gravity. (The optional 100 um capillary is recommended for this mode.)

SMDE (Static Mercury Drop Electrode) - the drop size is determined by the length of time for which the fast-response capillary valve is opened, and the drop is dislodged by a drop knocker. The dispense/knock timing is microprocessor-controlled and is typically coordinated with the potential pulse or square-wave waveform. This mode can also used to generate the Hanging Mercury Drop Electrode required for stripping experiments.

CGME (Controlled Growth Mercury Electrode) - the mercury drop is grown by a series of pulses that open the capillary valve. The number of pulses, their duration, and their frequency can be varied by PC control, providing great flexibility in both the drop size and its rate of growth. This CGME mode can be used for both polarographic and stripping experiments.

http://www.basinc.com/products/ec/cgme.php

BASi EC-epsilon 2 Autoanalyzer

Supplied Description:

http://www.basinc.com/products/ec/epsilon/

Instrument Type

Generic Name: BASi EC-epsilon 2 Autoanalyzer

Acronym: BASi EC-epsilon 2

Generic Description:

The Bioanalytical Systems EC epsilon is a family of potentiostat/galvanostats for electrochemistry. The most basic epsilon instrument can be used for standard techniques, as well as chronopotentiometry for materials characterization (e.g., characterization of transition metal complexes by cyclic voltammetry and controlled potential electrolysis, or of biosensors by cyclic voltammetry and constant potential amperometry). Pulse, square wave, and stripping techniques can be added by a software upgrade, and a second channel can be added by a hardware upgrade.

http://www.basinc.com/products/ec/epsilon/

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
cruise_id	cruise identification	unitless	cruise_id
station	station number	unitless	station
date	GMT date when rosette cast was started; formatted as yyyymmdd	unitless	date
lat	Station latitude; north is positive: position when sampling cast was started (2 m sample = underway sample collected typically on approach to station)	decimal degrees	lat
lon	Station longitude; east is positive; position when sampling cast was started (2 m sample = underway sample collected typically on approach to station)	decimal degrees	lon
depth	sample collection depth below sea surface	meters	depth
depth_w	water column depth at sampling location	meters	depth_w
N_TITRATIONS	number of titrations performed for sample analyses	unitless	num_reps
Fe_D_CONC_BOTTLE	Dissolved iron (Fe) concentration value used in the speciation data interpretation. Data received from Mak Saito’s lab at Woods Hole Oceanography Institution; contact Saito for additional information. Units	nanomoles/liter (10^-9 M)	Fe
L1Fe_D_CONC_BOTTLE	concentration of dissolved iron-binding ligand with log K1 = 12. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L1_FLAG	L1 quality flag	unitless	q_flag
L1_stdev	standard deviation of averaged results from replicate analyses; only available for samples with n>1 titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	nanomoles/liter (10^-9 M)	std_dev
L1Fe_D_LogK_BOTTLE	log conditional stability constant of L1 complexes with iron (log). "not_detected" used when this parameter was not determined in sample analyses.	No units; K1 has units of M-1	no_bcodmo_term
log_K1_FLAG	K1 quality flag	unitless	q_flag
log_K1_stdev	standard deviation of averaged results from replicate analyses; only available for samples with n>1 titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	No units; K1 has units of M-1	std_dev
L2Fe_D_CONC_BOTTLE	concentration of dissolved iron-binding ligand with log K2 = 11-12. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L2_FLAG	L2 quality flag	unitless	q_flag
L2_stdev	standard deviation of averaged results from replicate analyses; only available for samples with n>1 titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	nanomoles/liter (10^-9 M)	std_dev
L2Fe_D_LogK_BOTTLE	log conditional stability constant of L2 complexes with iron (log). "not_detected" used when this parameter was not determined in sample analyses.	No units; K2 has units of M^-1	no_bcodmo_term
log_K2_FLAG	K2 quality flag	unitless	q_flag
log_K2_stdev	standard deviation of averaged results from replicate analyses; only available for samples with n>1 titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	No units; K2 has units of M^-1	std_dev
L3Fe_D_CONC_BOTTLE	concentration of dissolved iron-binding ligand with log K3 = 10-11. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L3_FLAG	L3 quality flag	unitless	q_flag
L3_stdev	standard deviation of averaged results from replicate analyses; only available for samples with n>1 titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	nanomoles/liter (10^-9 M)	std_dev
L3Fe_D_LogK_BOTTLE	log conditional stability constant of L3 complexes with iron (log). "not_detected" used when this parameter was not determined in sample analyses.	No units; K3 has units of M^-1	no_bcodmo_term
log_K3_FLAG	K3 quality flag	unitless	q_flag
log_K3_stdev	standard deviation of averaged results from replicate titrations; only available for samples with replicate titrations. "nd = no data" used when standard deviations were not available either because of single replicate sample analyses or this ligand classes was not detected in the analyses.	No units; K3 has units of M^-1	std_dev

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Dataset: Dissolved iron speciation - CoFeMUG KN192-05