Sediments were recovered from Cores 191-1179B-1H through 4H under N2 atmosphere to minimize exposure to oxygen. A part of each sample was packed in an airtight bag. These samples were used for XANES analysis to determine the oxidation states of Mn and Ce. The remainder of each sample was washed twice with Milli-Q water and dried for chemical analysis.
The major element composition of the sediment samples were determined by X-ray fluorescence (XRF) spectroscopy (Rigaku ZSX-101e). The samples were dried overnight at 110°C. The fusion glass was made from a mixture of sample (2.00 g), flux (4.00 g; Li2B4O7:LiBO2 = 1:4, Johnson Matthey Spectro flux 100B), and LiNO3 (0.60 g). Details of the procedure used for the XRF analysis are found in Kanazawa, Sager, Escutia, et al. (2001). Abundances of the REE were measured using an inductively coupled plasma–mass spectrometer (ICP-MS) as described previously (Takahashi et al., 2002b). Approximately 0.1 g of sediment sample was first digested in a mixture of HClO4 and HF, and the solution was then redissolved into HClO4 after being dried. The sample was redissolved in HCl and evaporated. The residue was redissolved using 2% HNO3 for measurement with ICP-MS using In and Bi as internal standards.
XANES spectra were recorded at BL-12C in the Photon Factory, KEK (Tsukuba, Japan) (Nomura and Koyama, 1996), or at BL01B1 in SPring-8 (Hyogo, Japan) (Uruga et al., 1999). Experimental procedures are similar to those in Takahashi et al. (2002a). A Si(111) double-crystal monochromator was used to obtain the incident X-ray beam. The energy step was typically 0.25 eV. The energy of the peak top did not shift >0.25 eV throughout all measurements. All spectra were collected in the fluorescence mode with the sample positioned at an angle of 45° with respect to the beam. The fluorescence yield was measured using a 19-element Ge semiconductor detector. It was necessary to correct the single-channel analyzer windowed signal because of the increase in dead time when the incoming count rate was high because of the large intensity from fluorescence and scattered X-rays.