Dataset: GP16 Trace Metals Dissolved

Analysis:
Samples were analyzed with an adaptation of Biller and Bruland (2012). For this method, 24 mL of sample was pipetted into 30 mL teflon jars with quartz lids, and spiked with In and Lu to 5 nM (natural concentrations of In and La are sub pM, so this spike overwhelms the natural concentrations). This In and Lu spike is used as a check of consistent recovery across different resin columns and sampling days. The samples were UV irradiated for 2 hours to break the chelation of the organic complexes on Co and Cu. We had observed that 2 hours in our UV irradiation box is sufficient to plateau the concentrations of Cu and Co. After UV irradiation, samples lids were changed from lids with quartz-inserts to fully-teflon lids, and the samples were allowed to sit at least overnight.

Samples were pre-concentrated on resin columns of Nobias-chelate PA1 resin (IDA and EDTA functional groups). We use 8 columns at a time, and therefore pre-concentrate 8 samples at a time. Columns are stored in weak (~0.1N) HNO3, and every day before samples are analyzed, the columns are cleaned with alternating pH 6 seawater, 1N HNO3, and pH 6 rinse/conditioning solution (0.05M NH4Ac). Just before pre-concentration on resin columns, 8 samples were buffered to pH 5.7-6.2 with an NH4Ac buffer, inverted and weighed. For each set of samples, the columns are conditioned with the rinse/conditioning solution (to get the columns the correct pH before the sample arrives), then loaded with the sample, then rinsed with the rinse/conditioning solution (to remove the salts) and then eluted with ~1 mL of 1M quartz-distilled HNO3. The eluent vials are weighed before and after elution, and the (now empty) sample jars are weighed as well. This method results in a concentration factor of about 24.

Column blanks were determined for each column by following the same procedure for samples, but loading a low-metal seawater for just 1 min rather than the 40 min a sample usually takes to load. Reagent blanks were determined by analyzing low-metal seawater twice normally (rx1) and twice with double the reagents (rx2; reagent doubled include the acid used to originally acidify the sample, the buffer used to get the sample to pH 5.7-6.2, and the In/Lu spike). In this way, the rx2 sample was the correct pH for analysis, but contained twice the amount of blank from the reagents. The difference between the rx2 and rx1 was used as the reagent blank.

Standards were made by spiking low-metal seawater and analyzing the standards in the same manner as the samples. The resulting standard curve was compared with a standard curve made in clean eluent. This allowed us to calculate and monitor the percent recovery of each metal over time. We also had a Mo standard curve that allowed us to correct for the MoO interference on Cd.

We analyzed samples, reference samples, standards and blanks in the Thermo-Element high resolution XR ICP-MS at UCSC. Consistently throughout the XR run, we ran clean eluent and a QC, to monitor drift of the instrument and changes in the instrument blank. We used the clean eluent as our “instrument blank.” To monitor drift in the blank of our columns and preconcentration procedure, we also ran “internal QC” samples, which are seawater samples from a large volume of homogenous seawater that our lab analyzed once every ~16 samples. We also ran every 4th sample in duplicate.

Data Processing:
We used the seawater standard calibration curve for each metal. We subtracted the instrument, column, and reagent blanks from each metal. We monitored the percent recovery for each metal and checked that reference samples analyzed and processed in the same way resulted in reasonable values.

We had a frequent contamination issue with Cu, Ni and Zn contamination, which we observed in the same ratios across many samples. We have had this problem in the past in our lab, but have yet to determine the cause. Due to the consistent ratios in the contamination, this was easily spotted and the impacted data removed from the dataset.

DMO notes:
took out first column. put it in header description.
changed 'nodata' to nd
took out 'n/a' in last station; replaced with nd. (illegal character)
changed precision of measurements to reflect PI instructions:
- Round to one decimal place: Y, Cd, Pb, Co, Ga
- Round to two decimal places: La, Ce, Sc, Mn, Fe, Ni, Cu, Zn
- changed variable names to conform to NAT and current GT where applicable
Joined and split into BOTTLE and FISH

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.