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Sampling was performed aboard the RV Blue Heron during cruise BH15-11, which sailed from Duluth MN to Duluth MN during August 2015. Best-practice metal-clean protocols were followed to the greatest extent possible before, during, and after the cruise using only acid-washed sample containers, filters, labware, etc. Particulate sampling comprised one cast at FWM and two casts at WM. The first water drawn from each Nisken was used to fill a 20 mL high-density polyethylene bottle for analysis of total dissolvable barium concentrations and barium-isotopic compositions; the remaining water (~8 L) was transferred to 10 L low-density polyethylene cubitainers to be taken below deck for filtration.
\nSamples were filtered immediately after collection using negative pressure from a central vacuum line. Each sample was drawn across a polyethersulphone filter membrane (0.45 \u03bcm cutoff) from a collapsible cubitainer. Filters were held in place using acid-cleaned Swinnex filter holders (EMD Millipore) and connected to the tubing lines with Luer taper fittings; filters were stored before and after use in sealed polycarbonate petri slide holders and manipulated using plastic forceps. Filtration proceeded for a minimum of three hours or until the filters clogged, at which point the filters were removed from their holders, stored, and the water level recorded; filtered volumes ranged from 0.5-3 L.
\nParticulate samples were prepared for analysis by leaching in 0.6 M hydrochloric acid at 80 \u00b0C for \u226516 hours. Total dissolvable (i.e. unfiltered) samples were weighed and acidified with hydrochloric acid to a concentration of 0.01 M. Samples were left to equilibrate for several months before any sample processing took place.
\nFollowing multi-element geochemical analyses\u2014but before ion-exchange chromatography\u2014all samples were dried and spiked with an appropriate amount of barium double spike to ensure the ratio of spike- to sample-derived barium was between one and two. Samples were additionally fluxed in a 1:1 mixture of concentrated hydrogen peroxide and nitric acid for \u226516 hours at 135 \u00b0C to oxidize any organic matter in the sample that could interfere with column chemistry or mass spectrometry.
\nProblem report:
\nTwo minor issues to note:
\n- The shallowest particulate samples contained insufficient barium to perform a precise isotopic measurement. As such, samples from these depths were \u2018pooled\u2019 to yield a depth-integrated value; the depth noted for these pooled samples reflects the average depth of the pooled sample, weighted by the fractional contribution to the total (measured) barium present in each pooled sample. This pooling does not apply to the multi-element geochemical data as these measurements were performed on separate aliquots.
- One sample yielded an anomalous total particulate titanium concentration (002.02.12) and one sample yielded an anomalous total particulate aluminum concentration (002.02.10); these have been listed as \u2018nd\u2019.
This dataset includes geochemical profiles of water samples collected in August 2015 at two stations in the western arm of Lake Superior.
\nThese data were published in:
\nTristan J. Horner, Helena V. Pryer, Sune G. Nielsen, Peter W. Crockford, Julia M. Gauglitz, Boswell A. Wing & Richard D. Ricketts (2017) Pelagic barite precipitation at micromolar ambient sulfate. Nature Communications 8, Article number: 1342 (2017) doi:10.1038/s41467-017-01229-5
Other relevant files and publications:
\nHorner, T. J., Kinsley, C. W., & Nielsen, S. G. (2015). Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation. Earth and Planetary Science Letters, 430, 511-522.
Elemental quantification in sample solutions was achieved via comparison of blank-corrected ion beam intensities to those of a reference curve constructed from measurement of eight standards with known concentrations (seven serially diluted standards plus origin). Ion beam intensities of barium, cadmium, and yttrium were measured in low-mass resolution mode whereas aluminum, calcium, iron, manganese, phosphorus, strontium, titanium, and vanadium were measured in medium-mass resolution mode; In was monitored in both modes and internal normalization was performed separately for low- and medium-mass resolution elements. Analytical uncertainties from ICP-MS analysis refer to the propagated uncertainties from ion counting statistics, In normalization, and from the goodness-of-fit of the standard reference curve. Measured concentrations were converted to Lake Superior particulate concentrations by subtracting the blank from the leachate and then normalizing by the measured volume of water passed through each filter.
\nBarium-isotopic data reduction was performed using baseline-corrected ion beams corresponding to m/z 131 (Xe, xenon), 135 (Ba), 136 (Xe; Ba; Ce, cerium), 137 (Ba), 138 (Ba; La, lanthanum; Ce), 139 (La) and 140 (Ce), which were measured simultaneously. Barium-isotopic compositions were calculated using the three-dimensional geometric interpretation of the double spike problem, with data reported in parts per one thousand deviations (\u2030) relative to NIST SRM 3104a.
\nBCO-DMO Processing Notes:
\n- added conventional header with dataset name, PI name, version date
\n- modified parameter names to conform with BCO-DMO naming conventions