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doi:10.2204/iodp.proc.346.203.2017

Methods and materials

Interstitial water collection

Interstitial water samples were extracted from sediment cores using two methods: whole-round squeezing and Rhizon sampling (see the “Methods” chapter [Tada et al., 2015a]). In general, two whole-round samples were taken per core, usually at the base of Sections 1 and 4. Rhizon samples then were obtained at higher resolution in Holes B and C, especially where Hole A showed major changes in chemical gradients. This combined strategy resulted in an IW sample approximately every 25–50 cm over the upper 40 m at Sites U1426 and U1427. Separate aliquots were taken from the IW samples for a range of measurements. On the ship, this included salinity, alkalinity and pH, major anions (Cl^–, SO₄^2–, Br^–) and cations (Ca, Mg, K, Na), minor elements (B, Ba, Fe, Li, Mn, Sr), ammonium (NH₄⁺), phosphate (PO₄^3–), silica (H₄SiO₄), hydrogen sulfide (HS^–), and “yellowness.” The results of these analyses were presented in the “Site U1426” and “Site U1427” chapters (Tada et al., 2015b, 2015c).

A separate set of IW aliquots, each between 0.5 and 5 mL in volume, were placed in 3 mL plastic vials, “preserved” by adding 10 µL of ultrapure HNO₃, and stored in a shipboard refrigerator. Following the expedition, these aliquots were shipped to Houston, Texas, but stayed in customs for several weeks. When the samples arrived at Rice University, they were immediately placed in refrigerators; however, they likely reached ambient temperatures while in customs.

Interstitial water analyses

A total of 134 IW samples from Site U1426 (105) and U1427 (29) were reanalyzed (Table T1). For 29 of these samples, replicate analyses were made to assess analytical precision. Shore-based analyses occurred on 31 December 2013 (52), 13 January 2014 (83), and 18 January 2014 (28), 95–113 days after the expedition (Table T2). However, no damaged or otherwise compromised vials were observed.

Concentrations of S, Ba, and Fe were measured with an Agilent Vista Pro ICP-AES housed in the geochemistry facilities at Rice University. Standards were prepared by diluting International Association for the Physical Sciences of the Ocean (IAPSO) P-series seawater and Fisher Scientific reference standard certified solutions of known concentrations (Gieskes et al., 1991). IW samples were diluted 1:20 with deionized water (>18 MΩ resistivity). Scandium (10 µL; NIST-traceable certified reference material) was added to standards and samples to correct for instrumental drift (Sc emission line = 361.383 nm). Wavelengths used for elemental analysis were 181.972, 493.403, and 238.204 nm for S, Ba, and Fe, respectively.

Two blanks and one S and Ba standard solution spiked control sample were placed every 20 samples. Of the duplicate samples, 21 of the 29 were analyzed on a different day than the original. The method detection limit (MDL) for each species is determined by the following equation (Skoog et al., 2007):

where C = concentration and I = intensity (counts per second on the ICP-AES).

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