Index properties measurements on Core 17H included bulk water content, dry water content, bulk density, grain density, dry density, porosity, and void ratio (Table 1). The measurements were collected on board ship following standard ODP procedures using the weight of the wet samples and the weight and volume of the dry samples (Lyle, Koizumi, Richter, et al., 1997).
The CaCO3 content of the Core 17H samples was determined using the modified vacuum-gasometric technique method (Jones and Kaiteris, 1983). The samples were dried for 12 hr in a 110°C oven and then crushed. Approximately 150-200 mg of sample was weighed, and 3 cm3 of 50% solution of phosphoric acid was used for analysis. A control sample consisting of pure calcium carbonate was analyzed every 10 samples, yielding an analytical precision of better than 2 wt%. The replicated analyses of 50 samples were performed in the Boise State University geochemistry laboratory (M. Lyle, pers. comm., 1998). The reproducibility of the measurements was within 1.5 wt% of the absolute value.
For biogenic opal extraction (Table 1), Mortlock and Froelich's technique was applied (Mortlock and Froelich, 1989), except that acetic acid buffered with sodium acetate was used instead of HCl to digest the carbonates, and the Si extraction was performed for 6 hr instead of 5 hr using hot Na2CO3 (D. Murray, pers. comm., 1997). Although samples were ground, there were diatom and radiolarian parts in the residues. This was quantified by sieving several leach residues at 38 µm, and the portion >38 µm was treated with a hot NaOH solution for 6 hr. Most of the biogenic Si was dissolved using the standard technique, but the remaining portion resulted in the small underestimation of the total opal content. The percent of underestimation of the total opal varies from 2.24 to 17.29 wt% with an average of 7.37% and is of a nonsystematic nature. This error has to be taken into consideration to use the data for quantitative studies (Table 2). The remaining sample residues were not sieved to avoid doubling the analytical time and cost.