Dataset: GP16 Dissolved iron speciation
Deployment: TN303

Dissolved iron speciation from 2013 U.S. GEOTRACES Eastern Pacific Zonal Transect

Principal Investigator:

Kristen Nicolle Buck (University of South Florida, USF)

BCO-DMO Data Manager:

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

Project:

U.S. GEOTRACES East Pacific Zonal Transect (GP16) (U.S. GEOTRACES EPZT)

US GEOTRACES Pacific Section: Measurement of the organic complexation of dissolved iron, copper and cobalt, and total dissolved cobalt (EPZT Fe Cu Co)

Deployment Synonyms:

GP16, GEOTRACES EPZT, GEOTRACES East Pacific Zonal Transect (EPZT), GT13, 325020131025

Version Date:

2016-12-07

Data URL:

https://www.bco-dmo.org/dataset-deployment/668560/data

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Description

Dissolved iron-binding organic ligand concentrations and conditional stability constants from surface GeoFish and GO-FLO water column samples collected in 2013 during the U.S. GEOTRACES GP16 cruise in the Eastern Pacific between Peru and Tahiti on the R.V. Thomas G. Thompson, cruise TN303.

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.

* To access the data with the FISH and BOTTLE data merged, see: http://data.bco-dmo.org/jg/serv/BCO/GEOTRACES/EPZT/Fe_spec_EPZT_joined.html0%7Bdir=data.bco-dmo.org/jg/dir/BCO/GEOTRACES/EPZT/,info=data.bco-dmo.org/jg/info/BCO/GEOTRACES/EPZT/Fe_speciation%7D

Methods & Sampling

Dataset acquisition description

Sample collection and filtering: Water column samples were collected by the U.S. GEOTRACES sampling team from 24 modified 12-L Teflon-coated GO-FLO samplers (General Oceanics) deployed on the GEOTRACES clean CTD rosette system (Cutter and Bruland 2012). The U.S. GEOTRACES sampling team filtered the samples through 0.2 µm 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, “GeoFish”, deployed to collect surface samples from outside the wake of the ship. Seawater from the GeoFish was pumped directly into the Bruland lab clean air laboratory van and filtered through 0.2 µm Supor Acropak filter cartridges.

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 University of South Florida for laboratory-based analyses post cruise.

Dissolved iron speciation (organic complexation) analyses: Dissolved iron speciation (organic complexation) was analyzed using competitive ligand exchange- adsorptive cathodic stripping voltammetry (CLE-AdCSV) with salicylaldoxime as the added competing ligand (Buck et al. 2015), modified from the original Rue and Bruland (1995) method. A borate-ammonium buffer was added to all vials, for a final pH of 8.2 (NBS scale; Buck et al. 2007, 2012). Dissolved iron additions of 0 to 10 nM were used in the titrations, for a total of at least 15 points in each titration. These dissolved iron additions were chosen to match those of the U.S. GEOTRACES North Atlantic dataset and include additional datapoints within this range to allow higher resolution data within titrations (Buck et al. 2016). Deposition times of 90 to 600 s were applied to the analyses, with typically longer deposition times for deeper water column samples. CLE-AdCSV 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 measurements of iron in seawater, though this method has been shown to compare well with other labs and techniques in 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

Dataset Processing Description

CLE-AdCSV data was interpreted using a freely available interpretation program, ProMCC (Omanovic et al. 2015; https://sites.google.com/site/mccprosece), which employs matrix based optimization of titration data fitting to obtain ligand concentrations and conditional stability constants for each sample. Uncertainties in the fitted parameter are presented as the 95% confidence interval provided by the interpretation program. When replicate titrations were conducted, results were presented as averages of the replicates.

Dissolved iron (DFe) concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) in Peter Sedwick’s lab at Old Dominion University were used in the ProMCC interpretation program 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’s EPZT dataset for the complete dissolved iron data and metadata.

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. In the U.S. GEOTRACES North Atlantic dataset using the same analytical techniques, samples from two stations were analyzed in triplicate complete titrations, typically two conducted shipboard and one in the laboratory after storing frozen (-20 ºC). 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 values of this ligand class, from the same profiles, the average standard deviation was 0.15 (log units).

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., 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.

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.

Cutter, G., P. Andersson, L. Codispoti, P. Croot, R. Francois, M. Lohan, H. Obata, and M. Rutgers van der Loeff [eds.]. 2010. Sampling and sample-handling protocols for GEOTRACES cruises version 1.0 ed. GEOTRACES.

Cutter, G. A., and K. W. Bruland. 2012. Rapid and noncontaminating sampling system for trace elements in global ocean surveys. Limnology and Oceanography: Methods 10: 425-436.

Omanović, D., C. Garnier, and I. Pižeta. 2015. ProMCC: An all-in-one tool for trace metal complexation studies. Marine Chemistry 173: 25-39.

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.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- column names reformatted to comply with BCO-DMO standards
- replaced 1 blank cell with nd, 'no data'
- joined with the master file to get columns: GEOTRC_EVENTNO, GEOTRC_INSTR, ISO_DATETIME_UTC_START_EVENT

Additional GEOTRACES Processing

As was done for the GEOTRACES-NAT data, BCO-DMO added standard US GEOTRACES information, such as the US GEOTRACES event number, to each submitted dataset lacking this information. To accomplish this, BCO-DMO compiled a 'master' dataset composed of the following parameters:

cruise_id, EXPOCODE,SECT_ID, STNNBR, CASTNO, GEOTRC_EVENTNO, GEOTRC_SAMPNO, GEOTRC_INSTR, SAMPNO, GF_NO, BTLNBR, BTLNBR_FLAG_W, DATE_START_EVENT, TIME_START_EVENT, ISO_DATETIME_UTC_START_EVENT, EVENT_LAT, EVENT_LON, DEPTH_MIN, DEPTH_MAX, BTL_DATE, BTL_TIME, BTL_ISO_DATETIME_UTC, BTL_LAT, BTL_LON, ODF_CTDPRS, SMDEPTH, FMDEPTH, BTMDEPTH, CTDPRS, CTDDEPTH.

This added information will facilitate subsequent analysis and inter comparison of the datasets.

Bottle parameters in the master file were taken from the GT-C_Bottle and ODF_Bottle datasets. Non-bottle parameters, including those from GeoFish tows, Aerosol sampling, and McLane Pumps, were taken from the TN303 Event Log (version 30 Oct 2014). Where applicable, pump information was taken from the PUMP_Nuts_Sals dataset.

A standardized BCO-DMO method (called "join") was then used to merge the missing parameters to each US GEOTRACES dataset, most often by matching on GEOTRC_SAMPNO or on some unique combination of other parameters.

If the master parameters were included in the original data file and the values did not differ from the master file, the original data columns were retained and the names of the parameters were changed from the PI-submitted names to the standardized master names. If there were differences between the PI-supplied parameter values and those in the master file, both columns were retained. If the original data submission included all of the master parameters, no additional columns were added, but parameter names were modified to match the naming conventions of the master file.

See the dataset parameters documentation for a description of which parameters were supplied by the PI and which were added via the join method.

More information about this dataset deployment

Funding

Award Number	Funding Source
OCE-1441969	NSF Division of Ocean Sciences

Instruments

BASi Controlled Growth Mercury Electrode

Supplied Description:

For CLE-AdCSV analyses

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:

For CLE-AdCSV analyses

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/

CTD Sea-Bird

Supplied Name:

Supplied Description:

Instrument Type

Generic Name: CTD Sea-Bird

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/130/

Generic Description:

Conductivity, Temperature, Depth (CTD) sensor package from SeaBird Electronics, no specific unit identified. This instrument designation is used when specific make and model are not known. See also other SeaBird instruments listed under CTD. More information from Sea-Bird Electronics.

GeoFish Towed near-Surface Sampler

Supplied Name:

Supplied Description:

Instrument Type

Generic Name: GeoFish Towed near-Surface Sampler

Acronym: GeoFish

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/31/

Generic Description:

The GeoFish towed sampler is a custom designed near surface (<2m) sampling system for the collection of trace metal clean seawater. It consists of a PVC encapsulated lead weighted torpedo and separate PVC depressor vane supporting the intake utilizing all PFA Teflon tubing connected to a deck mounted, air-driven, PFA Teflon dual-diaphragm pump which provides trace-metal clean seawater at up to 3.7L/min. The GeoFish is towed at up to 13kts off to the side of the vessel outside of the ship's wake to avoid possible contamination from the ship's hull. It was developed by Geoffrey Smith and Ken Bruland (University of California, Santa Cruz).

GO-FLO Teflon Trace Metal Bottle

Supplied Name: 24 modified 12-L Teflon-coated GO-FLO samplers (General Oceanics)

Supplied Description:

Used for water sample collections

Instrument Type

Generic Name: GO-FLO Teflon Trace Metal Bottle

Acronym: GO-FLO Teflon TM

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/30/

Generic Description:

GO-FLO Teflon-lined Trace Metal free sampling bottles are used for collecting water samples for trace metal, nutrient and pigment analysis. The GO-FLO sampling bottle is designed specifically to avoid sample contamination at the surface, internal spring contamination, loss of sample on deck (internal seals), and exchange of water from different depths.

Parameters

Supplied Name	Supplied description	Supplied Units	Standard Name
cruise_id	cruise identification	unitless	cruise_id
station	station number	unitless	station
GEOTRC_SAMPNO	Unique identifying number for US GEOTRACES samples. PI-supplied values were identical to those in the intermediate US GEOTRACES EPZT master file	unitless	sample
GEOTRC_EVENTNO	Unique identifying number for US GEOTRACES sampling event. Added by BCO-DMO from the intermediate US GEOTRACES EPZT master file.	unitless	event
GEOTRC_INSTR	Unique identifying number for US GEOTRACES instruments. Added by BCO-DMO from the intermediate US GEOTRACES EPZT master file.	unitless	instrument
ISO_DATETIME_UTC_START_EVENT	Event start date/time (UTC) formatted to ISO8601 standard. T indicates start of time string; Z indicates UTC. Calculated from original date and time fields. Values were added from the intermediate US GEOTRACES EPZT master file (see Processing Description). Formatted as YYYY-mm-ddTHH:MM:SS.ssZ	year-month-day-hour-minute-second	ISO_DateTime_UTC
date	GMT date when rosette cast was started; formatted as yyyymmdd	year-month-day	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
Fe_D_CONC_BOTTLE	Dissolved iron (Fe) concentration value from bottle samples 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 from bottle samples 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
L1Fe_D_LogK_BOTTLE	log conditional stability constant from bottle samples of L1 complexes with iron (logK^cond FeL1.Fe'). "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_95pcnt_CI	95% confidence limit of log K1 determined from data fit by ProMCC. "nd = no data" used when maximum value of 13 assigned due to ProMCC returning values > 13 and large 95% CI indicating results outside of analytical window.	No units; K1 has units of M-1	no_bcodmo_term
L2Fe_D_CONC_BOTTLE	concentration of dissolved iron-binding ligand with log K2 = 11-12 from bottle samples. "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_95pcnt_CI	95% confidence limit of [L2] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term
L2Fe_D_LogK_BOTTLE	log conditional stability constant of L2 complexes with iron (logK^cond FeL2.Fe') from bottle samples. "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_95pcnt_CI	95% confidence limit of log K2 determined from data fit by ProMCC. "nd" = "not detected".	No units; K2 has units of M^-1	no_bcodmo_term
L3Fe_D_CONC_BOTTLE	concentration of dissolved iron-binding ligand with log K3 = 10-11 from bottle samples. "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_95pcnt_CI	95% confidence limit of [L3] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term
L3Fe_D_LogK_BOTTLE	log conditional stability constant of L3 complexes with iron (logK^cond FeL3.Fe') from bottle samples. "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_95pcnt_CI	95% confidence limit of log K3 determined from data fit by ProMCC. "nd" = "not detected".	No units; K3 has units of M^-1	no_bcodmo_term
Fe_D_CONC_FISH	Dissolved iron (Fe) concentration value used in the speciation data interpretation; from Fish samples. 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_FISH	concentration of dissolved iron-binding ligand with log K1 = 12; from Fish samples. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L1_FLAG_FISH	L1 quality flag	unitless	q_flag
L1Fe_D_LogK_FISH	log conditional stability constant of L1 complexes with iron (logK^cond FeL1.Fe'); from Fish samples. "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_FISH	K1 quality flag	unitless	q_flag
log_K1_95pcnt_CI_FISH	95% confidence limit of log K1 determined from data fit by ProMCC. "nd = no data" used when maximum value of 13 assigned due to ProMCC returning values > 13 and large 95% CI indicating results outside of analytical window.	No units; K1 has units of M-1	no_bcodmo_term
L2Fe_D_CONC_FISH	concentration of dissolved iron-binding ligand with log K2 = 11-12; from Fish samples. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L2_FLAG_FISH	L2 quality flag	unitless	q_flag
L2_95pcnt_CI_FISH	95% confidence limit of [L2] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term
L2Fe_D_LogK_FISH	log conditional stability constant of L2 complexes with iron (logK^cond FeL2.Fe'); from Fish samples. "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_FISH	K2 quality flag	unitless	q_flag
log_K2_95pcnt_CI_FISH	95% confidence limit of log K2 determined from data fit by ProMCC. "nd" = "not detected".	No units; K2 has units of M^-1	no_bcodmo_term
L3Fe_D_CONC_FISH	concentration of dissolved iron-binding ligand with log K3 = 10-11; from Fish samples. "not_detected" used when this parameter was not determined in sample analyses.	nanomoles/liter (10^-9 M)	trace_metal_conc
L3_FLAG_FISH	L3 quality flag	unitless	q_flag
L3_95pcnt_CI_FISH	95% confidence limit of [L3] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term
L3Fe_D_LogK_FISH	log conditional stability constant of L3 complexes with iron (logK^cond FeL3.Fe'); from Fish samples. "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_FISH	K3 quality flag	unitless	q_flag
log_K3_95pcnt_CI_FISH	95% confidence limit of log K3 determined from data fit by ProMCC. "nd" = "not detected".	No units; K3 has units of M^-1	no_bcodmo_term
L1_95pcnt_CI	95% confidence limit of [L1] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term
L1_95pcnt_CI_FISH	95% confidence limit of [L1] determined from data fit by ProMCC. Units "nd" = "not detected".	nanomoles/liter (10^-9 M)	no_bcodmo_term

Database

Contribute Data

Dataset: GP16 Dissolved iron speciation
Deployment: TN303

Dataset acquisition description

Dataset Processing Description

Database

Contribute Data

Dataset: GP16 Dissolved iron speciationDeployment: TN303

Dataset acquisition description

Dataset Processing Description

Dataset: GP16 Dissolved iron speciation
Deployment: TN303