Peak height (in nA) was measured relative to a linear baseline for the Co reduction peak ca. -1.15V. All seven scans (3 baseline and 4 standard additions) were used to determine a sample specific sensitivity (nA/pM Co added, mean r2 = 0.998). Cobalt concentrations were calculated from the baseline peak height, divided by the sensitivity and corrected from volume changes from sodium nitrite addition, followed by subtraction of the mean blank for at sea, or in lab analyses.

At sea analyses were characterized with mild to moderate electrical inference that mandated additional processing before peak height could be reliably measured. We adopted a simplified least squared fitting routine included in the NOVA software package that conducted a 15-point weighted moving average according to a 2nd order polynomial. This method did not distort cobalt concentrations when noise was low. A small fraction of scans (~2.6%) were not adequately fit using this routine and were instead smoothed using a 9-point linear moving average (22.1 mV window), also included in NOVA. For all samples peak height was measured manually to minimize distortion due to added noise. Subsequent investigation in the laboratory, on land, was able to remove this signal by increasing the current sampling step (but without changing the scan speed) from 2.46 mV to 4.88 mV, which eliminated the need for smoothing prior to sample analysis. We observed good agreement between samples analyzed at sea and in lab, indicating that the smoothing procedures applied at sea did not bias the data and that gas adsorbing satchels preserved original concentrations reasonably well.

On occasion, analyses were repeated due to obvious electrode malfunction or to confirm oceanographic consistency of measured values. If the repeated measurement was similar to the initial, the initial value is reported. If the repeated analysis was more oceanographically consistent with adjacent values in the water column, that analysis was used instead.

Flags for both total and labile cobalt follow WOCE conventions, where:

2 = Good value.
3 = Questionable value, due to need for increased smoothing of scan or loss of mercury drop during scanning.
4 = Bad value, identified by poor r2 of standard addition and/or large disagreement between triplicate baseline scans.
5 = No reported result because analysis was not performed or because of instrument malfunction.

BCO-DMO Processing:
- moved GeoFish data into separate columns per GEOTRACES naming conventions;
- replaced blanks with "nd" (no data);
- 17 July 2017: made dataset publicly available (was previously restricted to GEOTRACES PIs only).

Additional GEOTRACES Processing by BCO-DMO:
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 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.

cobalt_joined.csv