GRA) were converted into dry bulk densities (dry) using the equation
The weight percentage of the bulk parameter >63 µm (coarse fraction) was measured on 274 samples from Cores 188-1165B-4H through 14H and Core 188-1165C-7R. The sample resolution is 30 cm, equivalent to a time resolution of 5 to 15 k.y., depending on sedimentation rate. All bulk samples were freeze dried, and the total mass of the bulk sample was determined. No further disaggregation procedure was used. Sand content was determined after wet sieving at 63 µm. The >63-µm samples were wet sieved into three subsamples (63-125, 125-250, and 250-500 µm). The sand subsamples were dried and weighed.
Splits of 76 samples (1-2 per section) used for grain-size analyses were also measured for opal-A content. Homogenized dry bulk samples were analyzed using an automated leaching technique after Müller and Schneider (1993), which was shown to be reliable in an interlaboratory comparison (Conley, 1998). Silica was extracted by wet chemical means with 1-M NaOH, and concentrations of dissolved silica were measured by molybdate blue spectrophotometry. The proportion of biogenic silica was determined by graphical analysis of the absorbance vs. time plot (DeMaster, 1981). Resulting silica values were converted into weight percent biogenic SiO2 and are given as weight percent biogenic silica by assuming a uniform bound water content of 10 wt% within the opaline substance. According to Müller and Schneider (1993), the relative accuracy of the method is better than 2% for samples rich in biogenic silica and 4%-10% for samples with <10 wt% biogenic silica, respectively. Bonn et al. (1998) assumed an artificial background value of 1-2 wt% "pseudo-opal," caused by a partial leaching of clay minerals. In contrast, Hillenbrand and Fütterer (2001) measured opal contents down to 0.4 wt% on discrete samples, suggesting a negligible background opal signal. No correction was applied to the opal data reported here.
Data sets of magnetic susceptibility and bulk density measured with the shipboard multisensor track (MST) on Cores 188-1165B-1H through 17H and Core 188-1165C-7R (Shipboard Scientific Party, 2001) have been edited for erroneous measurements resulting from section breaks and voids. Section 188-1165-11H-5, which was not run on the MST during the cruise, was measured using a split-core logger located in the ODP core repository. Because of different measurement conditions, shore-based (MS point sensor, split cores, and dryer sediment) and shipboard (MS loop sensor, whole cores, and fresh sediment) corrections had to be made to the shore-based data sets. This was accomplished by remeasuring Section 188-1165-11H-6 with the split-core logger and from this deriving a linear correlation between ship- and shore-based data sets. The GRA bulk densities (GRA) were converted into dry bulk densities (dry) using the equation
dry = -1.5228 + 1.5432 x GRA.
The linear relationship between wet bulk density and dry bulk density measurements is derived from shipboard moisture and density measurements performed on discrete samples (Fig. F1). To quantify the correlation between the different parameters, the MST data were resampled at the exact depths for which grain size and opal-A data are available.
