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doi:10.2204/iodp.proc.320321.210.2013

Methods and materials

Archived pore water whole-round and Rhizon samples collected during Expedition 320/321 were analyzed simultaneously for dissolved nitrate and silicate concentrations. Samples were filtered and sealed in glass ampules during Expedition 320/321. Ampules were opened on the day of analysis. Samples and standards were diluted with glass-distilled water (6:1 for nitrate and 20:1 for silicate), and constituents were measured using an automated coulometric technique in a flow injection analysis system (Lachat QuickChem 8000 FIA) using standard methods (Parsons et al., 1984; Strickland and Parsons, 1968). When sample size was limited, measurements of nitrate were prioritized.

Standards were made from a stock solution of potassium nitrate, sodium fluorosilicate, and glass-distilled water. A consistency standard (a mixture of sodium nitrate, sodium fluorosilicate, and sodium chloride dissolved in glass-distilled water and kept under refrigeration) was processed and analyzed with each batch of samples for long-term calibration and quality control purposes. Analytical error on the consistency standard analyzed in multiple replicates (n = 57) over the course of several months was 48.6 ± 3.4 µM for nitrate and 722 ± 12 µM for silicate (Table T2). Detection limits, determined from replicates (n = 10) of the glass-distilled water used for dilution and run as samples were 0.7 ± 0.2 µM for nitrate and 1 ± 0.4 µM for silicate (Table T2).