Dissolved lead (Pb) along the US GEOTRACES East Pacific Zonal Transect from the R/V Thomas G. Thompson TN303 cruise in the Eastern Tropical Pacific, Peru to Tahiti during 2013 (NCEI Accession 0291317)

Acquisition Description:
Sampling:
Sample bottles were LDPE and cleaned in accordance with the GEOTRACES cookbook (). Sample bottles were stored in weak (~0.1 N) HNO 3 , and were emptied before shipping.

Samples were collected using the U.S. GEOTRACES sampling system of 24 Teflon-coated GO-FLO bottles (Cutter and Bruland, 2012). At each station, the bottles were deployed open and tripped on ascent at 3 m/min. GO-FLOs were sampled in the GEOTRACES trace metal clean sampling van that contained HEPA-filtered air.

During sampling, the GO-FLO bottles were pressurized to ~0.4 atm with HEPA-filtered air, and their spigots were fitted with an acid-cleaned piece of Bev-a-Line tubing that fed into an Acropak-200 Supor capsule filter (0.2 µm pore size made of polyethersulfone). Before use, this filter had been filled with filtered surface seawater that had been acidifed to pH 2 with trace metal clean HCl and left overnight to rinse. Before collecting any subsamples, at least 500mL of seawater was passed through the filter (while eliminating air bubbles in the capsule reservoir). Sample bottles were rinsed three times with 10% sample volume before filling. Acropak filters were used for at most 3 casts before a new filter was used, and they were stored empty in a refrigerator while not in use. GEOFish surface samples were taken using an all-plastic "towed fish" pumping system as described in Bruland et al. 2005 at approximately 3 m depth and were similarly filtered and sampled.

Samples were acidified at sea with the equivalent of 4mL quartz-distilled 6M HCl per liter of seawater (resulting in pH 1.7-1.8). Samples were sitting acidified for several months before analysis back in the laboratory.

Analysis:
Samples were analyzed using the method of Ndung’u et. al. (2003) with adaptations from Zurbrick, et. al. (2013). Aliquots of samples are poured in to 15mL LDPE bottles for analysis. Samples, blanks, reference materials and standards are all treated equally. They are buffered with trace metal clean ammonium acetate (pH 9) in line and sent across a Toyopearl AF-Chelate 650 M resin column. The column is rinsed with diluted ammonium acetate, and eluted in 1.5N quartz distilled nitric acid (with added bismuth as an internal standard) into the injector of the HR-ICP-MS. Counts of lead are measured throughout the elution, yielding a curve which is then integrated to give our raw values.

Standards are made by spiking lead into low concentration seawater. Blanks are 24mL HCl in Milli-Q. Reference materials used were SAFe S1, SAFe D2, and GEOTRACES reference samples GS and GD. Standard curves are run at the beginning and the end of runs and reference materials and blanks are run throughout (every 10 or less samples).