Dataset: GP16 Cu Ni Mn V

For analysis of dissolved V, Ni, Cu, and Mn, 14 mL of sample was spiked with a mixture of isotopically-enriched Ni-62, Cu-65, and V-50 (Oak Ridge Nat’l. Labs). Each spike was >90% enriched in the listed isotopes, except for V-50 (0.25% natural abundance) which was 44.3% enriched. The sample/spike ratio was chosen so as to have the analytical isotope ratios approximately the geometric mean of the natural and enriched spike isotope ratios. Samples were then extracted/pre-concentrated using a SeaFAST system (Elemental Scientific, Inc.) operated in offline mode. A 10-mL sample loop was employed and the elution volume was 750 µL. A similar online SeaFAST extraction procedure is described by Hawthorn et al. (2012) for rare earth elements. The extracted samples were subsequently analyzed using a Thermo-Fisher high resolution ICP-MS with an Apex-FAST high efficiency sample introduction system with Spiro desolvator (Elemental Scientific, Inc.). All elements were determined in medium resolution. For Mn-55 the V, Ni, and Cu spikes served as internal standards. Calibration was checked by analysis of a large-volume composite North Atlantic surface seawater sample. Spiked (with a natural isotopic abundance elemental spike) and unspiked aliquots of this sample were analyzed twice in each analytical run. Ti-47 and Cr-52 were monitored to correct for any Ti-50 or Cr-50 isobaric interference on V-50; the correction was generally <1%.

The reproducibility error of this method was estimated by comparing samples collected at the same depths on different casts at the same station. For 32 pairs of these replicate samples, the average absolute deviation was 0.8 nmol/kg or typically 2%. Repeated runs of US GEOTRACES intercalibration samples and in-house reference solutions suggest a precision of ±1.5%; the limit of detection for vanadium was ~0.5 nmol/kg. Recovery of the method, as determined by repeated analysis of a spiked and unspiked seawater sample was 99.5 ± 2.8%.

Data Version Information:

Current Version 20 Dec 2016 replaces the version from  08 Jun 2016. This change corrected V, Ni, Cu, and Mn data and data flags that were in the wrong column.  They were bottle samples and they were in the fish sample columns. After consulting the master event log to confirm they were bottle samples, the values were moved to the bottle column.

BCO-DMO Processing notes:

- variable names changed to conform to GEOTRACES conventions
- split GeoFISH data and bottle sample data into separate columns so GEOTRACES naming conventions of _BOTTLE and _FISH would be appropriate
- added DEPTH_FISH to distinguish between that and CTDDEPTH
- 20 Dec 2016, moved data from station 25 cast 1 from FISH to BOTTLE columns
- 04 March 2019: removed embargo on dataset.

Additional Information (including references) can be found in GEOTRACES Intercalibration Document 

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.