INTRODUCTION

Ocean Drilling Program (ODP) Site 1016 (34°32´N, 122°17´W) is located about 150 km west of Point Conception, California, on an abyssal hill in water 3835 m deep (Fig. 1). Although the Monterey Fan and the Arguello Fan extend to the north and south, respectively, of this abyssal hill (Chase et al., 1981), this site is covered with hemipelagic sediments. The core of southward flow of the California Current is located near this site (Hickey, 1979; Lynn and Simpson, 1987). The site is, therefore, suitable for reconstructing sea-surface temperature (SST) of the California Current and the intensity of its associated upwelling. The SST of the California Current is the result of mixing the West Wind Drift subarctic water and the North Pacific Current subtropical water (Hickey, 1979), and it is possibly sensitive to climate changes in the North Pacific Ocean and the surrounding areas. The coastal upwelling is induced by northerly winds along the California margin (Huyer, 1983), and the changes in its intensity affect primary productivity and the ecosystem (e.g., Parsons et al., 1984; Roemmich and McGown, 1995). Thus the assessments of paleo-sea-surface temperature (paleo-SST), primary productivity, and the marine ecosystem provide a clue to understanding the responses of the California Current system to Quaternary climate changes.

Many investigations have been conducted on the paleoenvironmental changes along the California margin, and most of them focused on the changes during the last 30,000 yr. ODP Site 893 provided 197-m-long core of sediments from the Santa Barbara Basin for high-resolution late Quaternary paleoenvironmental studies (Shore-based Scientific Party, 1994). During Leg 167, we drilled Sites 1016 (3846 m water depth) and 1017 (967 m water depth) at the open-ocean side of the Santa Barbara Basin. The location of Site 1016 is a hemipelagic, deep-sea site; therefore, the sediments record sensitively the changes of marine surface environment and carbonate compensation depth.

Assessments of paleo-SST were conducted using proxies of alkenones, foraminifers, radiolarians, and pollens during the last 30,000 yr at many locations along the California margin and during the last 160,000 yr at Site 893. Along the northern California margin, the paleo-SST estimated using (Prahl et al., 1995; Doose et al., 1997) agrees with those estimated using radiolarian assemblages (Prahl et al., 1995) and foraminiferal ¹⁸O and their assemblages (Ortiz et al., 1997), and both indicate about 4°C lower SST in the last glacial maximum (LGM; Stage 2) than the Holocene (Stage 1). In contrast, in the California Borderland, -derived SST disagrees with foraminiferal and pollen-derived SST during LGM. The -SST estimates indicate that LGM was 0°-2°C cooler than Holocene (Herbert et al., 1995; Hinrichs et al., 1997), whereas the SST estimations using sinistral/dextral ratio of N. pachyderma, ¹⁸O of planktonic foraminifers, and foraminiferal assemblages indicate that LGM was more than 5°C cooler than Holocene (Kahn et al., 1981; Kennett and Ingram, 1995; Kennett and Venz, 1995; Thunell and Mortyn, 1995; Mortyn et al., 1996). Pollen assemblages at Site 893 agreed with foraminiferal SST estimation (Heusser, 1995).

Primary productivity changes along the California margin were assessed based on the contents and accumulation rates of organic carbon, calcium carbonate, trace elements, and opaline skeletons. Along the northern California margin, changes in the organic carbon and diatom accumulation rates and trace metal concentrations suggest that the productivity during LGM was lower than Holocene (Lyle et al., 1992; Sancetta et al., 1992; Ortiz et al., 1997; Dean et al., 1997; Gardner et al., 1997), which was attributed to weaker coastal-upwelling-favorable northerly winds off northern California and Oregon during LGM (Lyle et al., 1992; Sancetta et al., 1992). The weaker upwelling during LGM was also indicated by Doose et al. (1997), who suggested the decreased intensity of the California Current during LGM, based on the increased SST gradient along the California margin. In the California Borderland, lower productivity during LGM than Holocene was suggested in the Santa Barbara Basin (Berger et al., 1997), whereas higher productivity was suggested in several other basins (Mortyn and Thunell, 1997). Mortyn and Thunell (1997) suggested that southerly migration of the North Pacific High resulted in upwelling intensification and increased productivity during LGM. In the Santa Barbara Basin, the studies of cores from Site 893 demonstrated the higher organic accumulation rates at Substages 5a, 5c, and 5e (Gardner and Dartnell, 1995: Stein and Rack, 1995), which was attributed to higher productivity at these periods (Stein and Rack, 1995).

The changes of carbonate compensation depth (CCD) in the last 300,000-yr were examined in the range 2700-4300 m deep along the northern California and Oregon margins, and it was suggested that the CCD has migrated more than 1800 m between glacial and interglacial times (Karlin et al., 1992). This large carbonate fluctuation was attributed to regional mechanisms, such as the glacial deep-water formation in the northern Pacific Ocean or the enhanced dissolution due to interglacial noncarbonate productivity related to coastal upwelling (Karlin et al., 1992). On the other hand, Gardner et al. (1997) found a carbonate preservation event at 10 ka in cores from the northern California margin and attributed it to the global mechanism, hypothesized by Broecker et al. (1993), that the expansion of boreal forests in the northern hemisphere removed CO₂ from the atmosphere and the surface water of the ocean, and in turn increased alkalinity of ocean water, which should have resulted in greater preservation of calcium carbonate.

The origin of organic matter in California and Oregon margin sediments was investigated in detail using various organic geochemical indicators including C/N value and Rock-Eval parameters (e.g., Rullkötter et al., 1981; Stein and Rack, 1995), lignin concentration (e.g., Hedges and Mann, 1979), and biomarker concentrations (e.g., Simoneit, 1977; Simoneit and Kaplan, 1980; Venkatesan et al., 1980; McEvoy et al., 1981; Louda and Baker, 1981; Simoneit and Mazurek, 1981; Rullkötter et al., 1981; Prahl and Carpenter, 1984; Venkatesan et al., 1990; Kennedy and Brassell, 1992; Hinrichs et al., 1995). Sediment trap samples were also examined for the biomarkers associated with sinking particles in the California Borderland (e.g., Crisp et al., 1979; Venkatesan and Kaplan, 1992). These studies indicate the contributions of marine algae, bacteria, and higher plants to the organic matter in California and Oregon margin sediments. In addition, petroleum-type components were characteristically observed in recent sediments (Simoneit and Kaplan, 1980; Venkatesan et al., 1980), late Pleistocene sediments (Hinrichs et al., 1995), and sinking particles (Crisp et al., 1979; Venkatesan and Kaplan, 1992) from the California Borderland, and their source was hypothesized to be anthropogenic pollution, submarine seep oils, and weathered matured petroleum source rocks.

In this preliminary study, we examine the changes of organic carbon and calcium carbonate contents, alkenone unsaturation indices, and biomarker concentrations in Core 167-1016C-1H, and discuss the responses of the marine ecosystem to climate changes during the late Quaternary, carbonate dissolution changes, and the origin of petroleum-type components in the sediments.