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doi:10.2204/iodp.proc.344.201.2015

Analytical methods

Pore fluid was collected from whole-round cores that were cut on the catwalk immediately after recovery, capped, and taken to the laboratory for processing using a titanium squeezer, modified after the stainless-steel squeezer of Manheim and Sayles (1974). Gauge pressures up to 30 MPa were applied using a laboratory hydraulic press to extract pore water. Pore fluid was passed through a prewashed Whatman No. 1 filter fitted above a titanium screen, filtered through a 0.2 µm Gelman polysulfone disposable filter, and subsequently extruded into a precleaned (10% HCl), 60 mL plastic syringe attached to the bottom of the squeezer assembly. Details of this procedure are given Expedition 334 Scientists (2012b) and in the “Methods” chapter (Harris et al., 2013d).

Strontium concentrations in pore fluids collected during Expedition 334 were measured postcruise by inductively coupled plasma–optical emission spectrometry (ICP-OES) at Oregon State University, as reported by Torres et al. (2014). During Expedition 344, pore fluid Sr concentrations were measured on board by inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and the data are reported in the “Expedition 344 summary” chapter (Harris et al., 2013a).

High-precision chloride concentrations were acquired on board during both Expeditions 334 and 344 using a Metrohm 785 DMP autotitrator and silver nitrate (AgNO₃). International Association for the Physical Sciences of the Oceans seawater was used as the standard (Expedition 334 Scientists, 2012b; see also the “Methods” chapter [Harris et al., 2013d]).

During Expedition 334, sulfate data were obtained using the shipboard ICP-AES, and the data are reported by Vannucchi, Ujiie, Stroncik, and the Expedition 334 Scientists (2012). During Expedition 344, sulfate concentrations were determined with a Metrohm 861.004 advanced compact ion chromatograph (IC). Details of the procedure and results are given in the “Methods” chapter (Harris et al., 2013d).

For analysis of the ⁸⁷Sr/⁸⁶Sr ratios, aliquots of acidified pore fluid samples containing ~300 ng Sr were directly loaded onto chromatographic columns. Samples were collected in acid-washed Nalgene bottles and acidified with ultrapure HNO₃ at a ratio of 20 µL acid per milliliter of sample. Strontium separation was carried out using 50 µL Sr-Spec resin from EICHROM. Isotopic analysis was performed using the NU multicollector inductively coupled plasma mass spectrometer (MC-ICPMS) housed in the W.M. Keck Collaboratory for Plasma Spectrometry in the College of Earth, Ocean and Atmospheric Science at Oregon State University (USA). Instrument mass bias was corrected using an ⁸⁸Sr/⁸⁶Sr ratio of 8.375209, and ⁸⁷Sr/⁸⁶Sr ratio data were normalized to the NBS 987 standard, with a reported ⁸⁷Sr/⁸⁶Sr ratio of 0.71025, with an internal error of ±0.00005 (2σ_mean; n = 91). Replicate analysis of an in house standard yielded a ⁸⁷Sr/⁸⁶Sr ratio of 0.70819 ± 0.00006 (2σ_mean; n = 79), representing our external error.

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