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doi:10.2204/iodp.proc.344.207.2017

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 (Manheim and Sayles, 1974). Gauge pressures up to 30 MPa were applied using a hydraulic press to extract pore fluids. The extracted 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 in the Methods chapter (Harris et al., 2013d).

High-precision chloride concentrations were acquired on board using a Metrohm 785 DMP autotitrator and silver nitrate (AgNO₃). International Association for the Physical Sciences of the Oceans (IAPSO) seawater was used as the standard (see the Methods chapter [Harris et al., 2013d]). The Cl concentrations were reanalyzed on shore at Scripps Institution of Oceanography by titration with AgNO₃ (1% precision).

Rubidium and cesium concentrations in the pore fluids were analyzed using a Thermo Scientific iCAP Q inductively coupled plasma–mass spectrometer (ICP-MS) in the Scripps Isotope Geochemistry Lab (SIGL) at Scripps Institute of Oceanography. Concentrations were determined using a calibration curve methodology.

A primary standard of 500 ppb Rb and 5 ppb Cs in 1% HNO₃ was diluted to 50%, 25%, 10%, 5%, and 1% concentrations with 1% 15 M ultra-pure (optima) HNO₃. For analysis, a 100 uL aliquot of 500 ppb indium standard was added to an empty, acid cleaned analysis vial. A 300 uL aliquot of this standard and 4.7 mL of 1% HNO₃ were added to the analysis vial. Additionally, 150 uL of a 560 mM NaCl solution was added to the analysis vial to account for matrix suppression of the plasma ionization efficiency. In total, the standard was diluted to 5.7% of its original concentration. The 25% standard was diluted as above and analyzed after every five samples throughout the analysis series to determine precision of the results. A blank solution was analyzed before and after the sample set was analyzed to determine residual carryover of any elements throughout the analysis.

Prior to sample analysis, the ICP-MS was calibrated using an internal indium (In) standard to maximize the intensity of the elements to be analyzed. Instrumental drift was corrected online by normalization of the intensity of the analyte with the intensity of the indium standard. A secondary drift correction was applied offline on each measured concentration using a 1.0 ppb indium calibration standard that was analyzed after every four samples.

Before diluting samples, a 100 uL aliquot of 500 ppb In standard was added to empty, acid cleaned analysis vials. Then a 300 uL aliquot of the sample and 4.7 mL of 1% HNO₃ were added to the analysis vial (diluting the sample to 5.7% of its original concentration) based on previous determination of the detection limits; previous attempts of 150 uL sample with 4.85 mL 1% HNO₃ proved to have low precision. There were 50 samples tested in total, 12 of which were duplicates to ensure conformity of results within samples.

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