MATERIAL AND METHODS

Hole 1017E consists of three cores composed of 24.9 m of grayish olive, homogeneous hemipelagic clayey silt to silty clay (Lyle, Koizumi, Richter, et al., 1997). Sand layers are relatively rare in the core but form a few thin (average 1-3 cm thick), medium- to fine-grained layers considered to be turbidites. These are largely associated with marine isotope Stages (MIS) 2 and 4 (Tada et al., Chap. 25, this volume). Core recovery exceeded 100%, and the depths used in this contribution have been corrected for this expansion. Stratigraphic evidence indicates that the top of Hole 1017E marks the sediment/water interface.

Hole 1017E was sampled at high stratigraphic resolution for oxygen isotopic analyses that were employed in the age model. Samples were continuously taken down the core, each with a thickness of 3 cm (15-cm³ volume). The raw samples were disaggregated in warm water, washed over a 63-µm sieve, and oven dried at 50°C. All of the samples contained sufficient numbers of benthic and planktonic foraminifers for isotopic analyses.

Specimens of the benthic foraminifer Uvigerina peregrina curticosta and the planktonic foraminifer Globigerina bulloides d'Orbigny were continuously present throughout and were picked for isotopic analyses. From five to ten specimens of Uvigerina and 10 to 20 specimens of G. bulloides from the >150-µm-size fraction were used for each stable isotopic measurement. Foraminiferal specimens are well preserved and show no evidence of diagenetic recrystallization of the calcium carbonate. Foraminifers in assemblages from Hole 1017E often contain infillings of pyrite, and specimens were picked with minimal amounts of pyrite.

Specimens selected for isotopic analysis were ultrasonically cleaned in reagent grade methanol, dried, and roasted under vacuum at 375°C for 1 hr to remove organic contaminants. The samples were reacted in orthophosphoric acid at 90°C with an on-line, automated carbonate CO₂ preparation device. The evolved CO₂ was then analyzed using a Finnegan/MAT 251 light stable isotope mass spectrometer at the University of California, Santa Barbara. Instrumental precision for ¹⁸O is 0.09 or better. All isotopic data are expressed using standard notation in per mil () relative to the Peedee belemnite (PDB) carbonate standard. Isotopic analyses were related to PDB through repeated analyses of NBS-19 with values, following Craig (1957), of ¹⁸O = -2.19. This contribution presents the oxygen isotopic data for Hole 1017E based on 794 analyses. The oxygen isotopic data are reported without corrections. Uvigerina has been shown to calcify its test close to oxygen isotopic equilibrium (Shackleton, 1974), whereas oxygen isotopic values for G. bulloides deviate from equilibrium by -0.27 (Bemis et al., 1998).

The age model for the upper part of Hole 1017E (<7.45 meters below seafloor) was constructed using 13 calendar-corrected ¹⁴C ages. The radiocarbon ages are based on 3.0- to 8.5-mg samples of mixed planktonic foraminifers. The planktonic foraminiferal samples were dominated by G. bulloides and Neogloboquadrina pachyderma, which were hand-picked. The samples were cleaned with deionized water and then leached with dilute HCl during ultrasonication. Dried samples were placed in individual reaction chambers, evacuated, heated, and then acidified with orthophosphoric acid at 90°C. The evolved CO₂ was purified, trapped, and converted to graphite in the presence of cobalt catalyst in individual reactors (Vogel et al., 1987). Graphite targets were measured at the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory (Davis et al., 1990).

Radiocarbon ages are reported using the Libby half-life of 5568 yr, following conventions defined by Stuiver and Polach (1977), and include a constant ¹³C correction of 0.900. A constant surface ocean reservoir correction of 633 yr is used for the calibration of ¹⁴C ages to calendar years. This value is the sum of the global surface-water reservoir-age correction of 400 yr from Stuiver and Braziunas (1993) and the regional reservoir-age correction (R) of 233 ± 60 yr from Ingram and Southon (1996).

Radiocarbon dates younger than 11,000 ¹⁴C age were converted to calendar ages using the reservoir-corrected age following Stuiver and Braziunas (1993). Radiocarbon dates older than 11,000 ¹⁴C age were converted to calendar ages using the equation from Bard et al. (1992):

corrected age [cal(BP)] = -5.85 × 10^-6 (A²) + (1.39A) - 1807,

where A equals the reservoir-corrected ¹⁴C age: i.e., ¹⁴C age - 630 yr.

This equation can be used to calibrate samples from 10,000 to 38,000 ¹⁴C yr. However, ages older than 22,000 ¹⁴C yr are constrained by only two points and could therefore be problematic. The resulting calibrated ages using the above two methods all fall within the maximum and minimum calibrated age ranges (one sigma) obtained from the latest ¹⁴C calibration data set, INTCAL98 (Stuiver et al., 1998). These are the same methods used to construct the age model for ODP Hole 893A in Santa Barbara Basin, which should facilitate the comparison of these two records.