Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Shipboard flow injection analysis (FIA) data of dissolved metals from the GT10 (KN199-04) cruise. Samples were collected using GO-FLO bottles and filtered through 0.2 µm Acropak filters. Concentrations and quality flags are reported for each metal.

Sampling Methods
The samples (with the exception of surface samples) were collected for trace metal determinations at 11 stations from the RV Knorr using a custom-built US GEOTRACES trace metal clean rosette consisting of an epoxy painted Al rosette frame containing 24x12 L GO-FLO bottles (Cutter and Bruland, 2012). Immediately after the package was recovered, the tops of the GO-FLO bottles were covered with plastic bags and the bottles were removed from the frame and carried into the US GEOTRACES clean van for sub-sampling. The GO-FLO bottles were pressurized to 10 psi using 0.2 µm-filtered compressed air and samples were filtered through 0.2 µm Acropak filters. All sub-sampling was undertaken in the clean van using rigorous trace metal protocols. Surface samples are from the towed fish surface sampling system.

Analytical Methods
FIA Sample Preparation: Samples were drawn into pre-numbered 125 ml PMP bottles after three rinses and were stored in plastic bags in the dark at room temperature before determination which was usually within 12 -36 hours of collection. Prior to determination samples were acidified by the addition of 125 ul sub-boiling distilled 6N HCl (hereinafter 6N HCl) and were microwaved in groups of 4 for 3 minutes in a 900 W microwave oven to achieve a temperature of 60+10 °C. Samples were allowed to cool for at least 1 hour prior to determination. Samples were determined in groups of 8.

FIA Standards: Shipboard mixed standards (Al and Fe, Mn) were prepared in the shore-based laboratory by serial dilution of commercial Al, Fe, and Mn standards (BDH Aristar) into distilled water which was acidified with the equivalent of 4 ml sub-boiled 6N HCl.  Standards for instrument calibration were prepared daily from filtered seawater by acidifying 1 L of low Fe seawater from a previous cast with 1 ml of 6N HCl and microwaving for 5 minutes to reach a temperature of 60 + 10°C.  After 1 hour, 200 + 2 ml of the cooled seawater was added to each of three 250 ml PMP bottles each of which had been rinsed three times with the microwaved seawater and shaken dry. Working standards were prepared by adding 0, +100µL, +200µL spikes of the shipboard mixed standard to these bottles, to yield a standard curve of +28.4nM and +56.81nM for Al, +1.26nM and +2.53nM for Fe, +5.11nM and +10.22nM for Mn. The system blank from the addition of the acid and buffer to samples was determined by double spiking a replicate sample i.e. by adding 2 x 125 ul 6N HCl and 5 ml of sample buffer to the replicate bottle and comparing the resulting signal to the original sample.

Dissolved Al Concentrations: Dissolved Al was determined using a Flow Injection Analysis scheme with fluorometric detection. Major components were a Rabbit peristaltic pump, a Dynamax FL-1 fluorometer, a Rainin A/D board and a Macintosh G3 computer running Rainin MacIntegrator v 1.4.3 to log and reduce data. The analytical scheme produces a complex between lumogallion and dissolved Al which when excited at 484 nm produces fluorescence at 552 nm.  Detailed description of the methodology is published in Resing and Measures (1994).

A 3-minute pre-concentration of sample (~9 ml) onto an 8-hydroxyquinoline (8-HQ) resin column yielded a detection limit of 1.02 and a precision of 1.94% at 17.58 nM.

Dissolved Fe: Dissolved Fe was determined using a Flow Injection Analysis scheme with spectrophotometric detection (Rainin Dynamax UV-C). Major components were a Rabbit peristaltic pump, a Dynamax FL-1 fluorometer, a Rainin A/D board and a Macintosh G3 computer running Rainin MacIntegrator v 1.4.3 to log and reduce data. The spectrophotometric detection of the iron eluted from the column is achieved through its catalytic effect on the oxidation of N,N-dimethylp-phenylenediamine dihydrochloride (DPD) the oxidised product is measured at 514 nm. Detailed description of the methodology is published in Measures et al (1995).

A 3-minute pre-concentration of sample (~9 ml) onto an 8-hydroxyquinoline (8-HQ) resin column yielded a detection limit of 0.064 nM and a precision of 3.1%.

Calculation of FIA data: Calculation of sample concentrations was by dividing the peak height derived from sample using the A/D software by the calculated slope of the standard curve. Variations in the slope of the standard curve during a day's run were corrected by the following procedure.

The change in the value of the slope of the standard curve between each run of standards was divided by the number of samples run between those standards to provide a calculated value for the slope of the standard curve at the point each sample was run. The value of the peak height for each sample was then recalculated by the estimated ratio of the standard curve slope at the point that sample was run. The estimate of the slope at each sample run is calculated by: (Initial slope + (incremental change per sample X # of samples run since initial standard was run)). The sample concentration is then calculated from the initial standard curve slope.

Data correction with shore-based ICPMS data
Shipboard determined dissolved Fe and Mn have been corrected using the shore-based ICPMS data that was measured by co-PI Dr. Jingfeng Wu. That data will be submitted separately. The corrected FIA data was calculated using the slope and the intercept of the correlation plot between the ICPMS data and FIA data on each of the days the FIA was run.

Shipboard dissolved Fe: Shipboard calculation:
The Fe concentration of samples was determined by dividing the sample peak height by the slope of the Fe standard solution. The standard curve was produced by adding +0 µL (+0 nM), +100 µL (+1.01 nM), +200 µL (+2.02 nM) of the shipboard standard solution into 200mL aliquots of seawater. This seawater was obtained from a 1L sample of seawater (usually from near the chlorophyll max) that had been filtered through a 0.2 µm pore-size Acropack cartridge, acidified with 1 ml of 6N HCl (sub boiling distilled) and microwaved to achieve a temperature of 60 + 10°C. A typical standard curve is shown in Figure 1 below.
 
Figure 1. Fe standard curve from the standard addition method. (click on the image to view a larger version)

The shipboard standard solution was 2.020 µM and had been prepared by gravimmetric dilution from a high purity standard solution (1000 µg/mL) at the shore-based laboratory of University of Hawaii. Overall precision is 3.1%, and the average detection limit is 0.064 nM.

Blank calculation:
At sea, the blank calculation of the data was made using the value derived from a sample that had been spiked with EDTA. This process yields a sample that should have no uncomplexed Fe thus allowing subtraction of the system blank.

Shore based adjustment of the shipboard data was made by comparison with the shore-based ICP MS data measured by J. Wu at U Miami. A plot of each station's data (FIA vs ICP MS) yielded a slope and intercept that was then used to recalculate the shipboard data. This indicated that the shipboard blank correction was underestimating the system blank.

Table: Slope and intercept between shipboard FIA (substituted EDTA blank) and ICPMS data
Station            Slope    Intercept    R2
USGT10-01     0.930    0.635           0.670
USGT10-03     0.644    0.316           0.868
USGT10-05     0.807    0.383           0.908
USGT10-06     0.930    0.112           0.910
USGT10-07     0.930    0.112           0.910
USGT10-09     1.183    0.051           0.909
USGT10-10     1.208    0.057           0.857
USGT10-11     1.150    0.091           0.863
USGT10-12     1.281    0.191           0.947

The ICPMS data reported by Miami (Dr. Wu) were only for full depth stations. One of the demi stations were determined at sea on the same day that full depth stations were run specifically GT10-06 and GT 10-07. Thus, these samples were adjusted using the same slope and intercept used for the full depth station. However, the other demi station samples were determined on separate days. Thus, the samples cannot currently be adjusted with existing ICPMS data.

The following demi stations have not been adjusted and are not reported: USGT10-02, USGT10-08.

Quality flags
Data have been flagged using the WOCE system of flags. Good is 2. Questionable is 3. Bad is 4. Samples that appear to be contaminated have been flagged 3.

Determination of contamination was by agreement with ICP MS data after adjustment (see above).

For dissolved Fe, samples in which both the ICP MS and the FIA data appear to be bad (not oceanographically consistent) have been flagged 4.

Flagged data from GT10 (2010 cruise):
Total reported sample count: 211
Flag 2 (Good): 175
Flag 3 (Questionable): 49
Flag 4 (Bad): 7

Accuracy results:
There are no shipboard results for the recoveries of Certified Reference Materials (CRMs) or consensus reference materials (e.g., SAFe water) as these samples are too acid to be run using this protocol. Instead these data are corrected using the shore-based ICP MS values which are calibrated against SaFe samples.

BCO-DMO Processing Notes
- Parameter names were modified to conform with BCO-DMO conventions.
- '-999' values were replaced with 'nd' to indicate 'no data'.
- The 'lon' parameter was calculated using the 'lon_360' values provided in the original data submission. (lon = lon_360 - 360).
- Original data submission received on 12/18/12 was replaced with updated data received on 12/21/12, in which a small error and quality flags have been corrected.
- Dataset updated to new version on 22 May 2013.
- The dataset was again updated to a newer version (including updates and error fixes) on 14 October 2013 (most recent version).

Additional GEOTRACES Processing:
After the data were submitted to the International Data Management Office, BODC, the office noticed that important identifying information was missing in many datasets. With the agreement of BODC and the US GEOTRACES lead PIs, 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: station_GEOTRC, cast_GEOTRC (bottle and pump data only), event_GEOTRC, sample_GEOTRC, sample_bottle_GEOTRC (bottle data only), bottle_GEOTRC (bottle data only), depth_GEOTRC_CTD (bottle data only), depth_GEOTRC_CTD_rounded (bottle data only), BTL_ISO_DateTime_UTC (bottle data only), and GeoFish_id (GeoFish data only). 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_GT10, GT-C_Bottle_GT11, ODF_Bottle_GT10, and ODF_Bottle_GT11 datasets. Non-bottle parameters, including those from GeoFish tows, Aerosol sampling, and McLane Pumps, were taken from the Event_Log_GT10 and Event_Log_GT11 datasets. McLane pump cast numbers missing in event logs were taken from the Particulate Th-234 dataset submitted by Ken Buesseler.

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 sample_GEOTRC 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.

Much of this text appeared in an article published in OCB News, October 2008, by the OCB Project Office.

The first U.S. GEOTRACES Atlantic Section will be specifically centered around a sampling cruise to be carried out in the North Atlantic in 2010. Ed Boyle (MIT) and Bill Jenkins (WHOI) organized a three-day planning workshop that was held September 22-24, 2008 at the Woods Hole Oceanographic Institution. The main goal of the workshop, sponsored by the National Science Foundation and the U.S. GEOTRACES Scientific Steering Committee, was to design the implementation plan for the first U.S. GEOTRACES Atlantic Section. The primary cruise design motivation was to improve knowledge of the sources, sinks and internal cycling of Trace Elements and their Isotopes (TEIs) by studying their distributions along a section in the North Atlantic (Figure 1). The North Atlantic has the full suite of processes that affect TEIs, including strong meridional advection, boundary scavenging and source effects, aeolian deposition, and the salty Mediterranean Outflow. The North Atlantic is particularly important as it lies at the "origin" of the global Meridional Overturning Circulation.

It is well understood that many trace metals play important roles in biogeochemical processes and the carbon cycle, yet very little is known about their large-scale distributions and the regional scale processes that affect them. Recent advances in sampling and analytical techniques, along with advances in our understanding of their roles in enzymatic and catalytic processes in the open ocean provide a natural opportunity to make substantial advances in our understanding of these important elements. Moreover, we are motivated by the prospect of global change and the need to understand the present and future workings of the ocean's biogeochemistry. The GEOTRACES strategy is to measure a broad suite of TEIs to constrain the critical biogeochemical processes that influence their distributions. In addition to these "exotic" substances, more traditional properties, including macronutrients (at micromolar and nanomolar levels), CTD, bio-optical parameters, and carbon system characteristics will be measured. The cruise starts at Line W, a repeat hydrographic section southeast of Cape Cod, extends to Bermuda and subsequently through the North Atlantic oligotrophic subtropical gyre, then transects into the African coast in the northern limb of the coastal upwelling region. From there, the cruise goes northward into the Mediterranean outflow. The station locations shown on the map are for the "fulldepth TEI" stations, and constitute approximately half of the stations to be ultimately occupied.

Figure 1. The proposed 2010 Atlantic GEOTRACES cruise track plotted on dissolved oxygen at 400 m depth. Data from the World Ocean Atlas (Levitus et al., 2005) were plotted using Ocean Data View (courtesy Reiner Schlitzer). [click on the image to view a larger version]

Hydrography, CTD and nutrient measurements will be supported by the Ocean Data Facility (J. Swift) at Scripps Institution of Oceanography and funded through NSF Facilities. They will be providing an additional CTD rosette system along with nephelometer and LADCP. A trace metal clean Go-Flo Rosette and winch will be provided by the group at Old Dominion University (G. Cutter) along with a towed underway pumping system.

The North Atlantic Transect cruise began in 2010 with KN199 leg 4 (station sampling) and leg 5 (underway sampling only) (Figure 2).

KN199-04 Cruise Report (PDF)

Figure 2. The red line shows the cruise track for the first leg of the US Geotraces North Atlantic Transect on the R/V Knorr in October 2010.  The rest of the stations (beginning with 13) will be completed in October-December 2011 on the R/V Knorr (courtesy of Bill Jenkins, Chief Scientist, GNAT first leg). [click on the image to view a larger version]

The section completion effort resumed again in November 2011 with KN204-01A,B (Figure 3).

KN204-01A,B Cruise Report (PDF)

Figure 3. Station locations occupied on the US Geotraces North Atlantic Transect on the R/V Knorr in November 2011.  [click on the image to view a larger version]

Data from the North Atlantic Transect cruises are available under the Datasets heading below, and consensus values for the SAFe and North Atlantic GEOTRACES Reference Seawater Samples are available from the GEOTRACES Program Office: Standards and Reference Materials

ADCP data are available from the Currents ADCP group at the University of Hawaii at the links below:
KN199-04   (leg 1 of 2010 cruise; Lisbon to Cape Verde)
KN199-05   (leg 2 of 2010 cruise; Cape Verde to Charleston, NC)
KN204-01A (part 1 of 2011 cruise; Woods Hole, MA to Bermuda)
KN204-01B (part 2 of 2011 cruise; Bermuda to Cape Verde)

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.