METHODS

Hole 1006A was sampled on board the JOIDES Resolution during Leg 166 with the idea of sampling additional selected intervals of Hole 1006B at the Core Repository in Bremen to bridge missing intervals in Hole 1006A. Sampling densities throughout Hole 1006A were typically one sample every 20 cm, although the sampling density was greater in several intervals. This study was designed to develop the stable isotope record to ~1.4 Ma, while our shipboard colleagues would extend the stable isotope record farther down into the Pliocene and Miocene. Biostratigraphic datum levels used in this study are given by T. Sato (unpubl. data).

Splits of each sample were oven dried at 60°C, weighed, and washed over a 63-µm stainless-steel mesh sieve. The coarse sediment fraction (>63 µm) was dry sieved through 250- and 355-µm mesh sieves. Tests of the planktonic foraminiferal species Globigerinoides ruber (d'Orbigny, 1839) were hand picked under a binocular microscope from the 250- to 355-µm sediment fraction. We have chosen G. ruber because it dwells in the mixed layer for all size fractions (Kroon and Darling, 1995). Tests were soaked in methyl alcohol (analytical reagent) for several minutes and later cleaned in an ultrasonic bath to remove adherent contaminants. Following ultrasonic cleaning, excess methyl alcohol was drawn off with tissue paper and any residual alcohol was allowed to evaporate. Foraminiferal sample weights were typically <0.1 mg and composed of 5-8 specimens. Following cleaning, foraminiferal tests were reacted in orthophosphoric acid (specific gravity = 1.9) at 90°C, and the resulting CO₂ gas was analyzed using a VG Isogas precision isotope ratio mass spectrometer located at the University of Edinburgh. Precision for oxygen isotope analysis was 0.08 (standard deviation for 100 analyses of an 'in-house' standard carbonate [SM1] conducted over several months). The oxygen isotope data for Holes 1006A and 1006B are given in Table 1 and Table 2.

Marine sediments accumulating on basin and ocean floors adjacent to shallow-water carbonate banks and platforms (<200 m water depth), termed "periplatform ooze" by Schlager and James (1978), consist predominantly of a mixture of carbonate platform-derived and planktonic-derived sediments (Boardman et al., 1986). The shallow-water carbonates have a different mineralogical composition than the deep-water carbonates. Modern tropical shallow-water carbonate sediments are primarily composed of aragonite and high-Mg calcite (HMC), with subordinate amounts of low-Mg calcite (LMC) (Friedman, 1965; Land, 1967; Milliman, 1974; Ginsburg and James, 1974). This mineralogy reflects the composition of the skeletal and nonskeletal components that dominate the shallow-water setting. In contrast, the mineralogy of deep-water carbonate sediments is largely controlled by the production of pelagic-driven carbonate and by the selective dissolution of the more soluble carbonate minerals (Friedman, 1965). Deep-water carbonate-rich sediments contain abundant LMC with minor amounts of aragonite and HMC.

The relative abundance of a variety of carbonate minerals present in Site 1006 sediments was quantified by X-ray diffraction (XRD). These minerals include aragonite, LMC, HMC, and dolomite. XRD was typically performed on ~0.5 g of the <63 µm fraction of the sediment. Each sample was oven dried at 60°C before being hand ground in an agate mortar (with analytical grade acetone) for exactly 4 min (Milliman, 1974). Individual samples were drawn up in a pipette, dispersed on a glass slide (2-cm diameter), smeared out to produce a sediment slurry of standard thickness and diameter, and dried at room temperature before being subject to X-rays. Each individually prepared sample was then analyzed using a Philips PW 1011/1050 automatic powder diffractometer (PW 1808 sample changer) at 40 kV and 50 mA through a scan from 5° to 40° 2q (Cu-ka) at a low scanning speed of 0.040° per second for optimal resolution. A calibration curve was produced for aragonite using a modified version of the sample-spiking method proposed by Gunatilaka and Till (1971) and Alexander (1996). The aragonite percentage data of Hole 1006A and 1006B are given in Table 1 and Table 2, respectively.