The California Current system is probably the best investigated eastern boundary current system in the world, with numerous studies of its physical dynamics, chemical structure, biological standing stocks, and biogeochemical fluxes. Nevertheless, the response of the California Current system and associated coastal upwelling systems to climate change is poorly documented. Climate models and available paleoceanographic data indicate that the California Current system changed dramatically with the growth and decay of the North American ice sheets. The paleoceanographic records, however, remain too sketchy to test the models (Kutzbach, 1987; Lyle et al.,1992).
Ocean Drilling Program (ODP) Leg 167 (Fig. 1) represents the first time since 1978 that the Pacific margin of North America will be drilled to study ocean history. It will collect both high-resolution records appropriate for study of the late Pleistocene, as well as long-term sediment records to examine the entire Neogene interval. The proposed drilling program will drill sites to understand the links between the evolution of north Pacific climate and the development of the California Current system. The same material will also be used to understand the links between the north Pacific and North American climate. Other important scientific objectives that could be pursued along this margin (e.g., the development of the Alaska Gyre, involving drilling along Canada and Alaska, or the investigation of climatic connections between the eastern north Pacific and the tropical Pacific, involving drilling along the Mexican continental margin) cannot be addressed in this program.
The last major drilling effort along the California margin, Deep Sea Drilling Project (DSDP) Leg 63, occurred immediately before the first deployment of the advanced hydraulic piston core (APC), and to date there is only one APC core in this climatically sensitive region, ODP Site 893, in the Santa Barbara Basin (Table 1, Kennett, J. P., Baldauf, J. G., et. al., 1994; Kennett, J. P., Baldauf, J. G., and Lyle, M. (Eds.), 1995). Recovered core from DSDP drilling is discontinuous and very disturbed, so it is impossible to use this material for modern high-resolution paleoceanographic studies. Reconnaissance studies have shown, however, that the Leg 167 survey area is highly sensitive to climate change (Fig. 2; Ingle, 1973). Strong climate signals are expected in the new ODP sites.
High-resolution studies of piston cores and the Site 893 drill site indicate that the region responds strongly to insolation changes. Strong signals that appear to be in the Milankovitch frequency bands are commonly observed. In addition, there appear to be suborbital frequency events that may be related to Dansgaard-Oeschger events in the Santa Barbara Basin (Behl and Kennett, 1995). What the sedimentary record reveals to us about Pleistocene paleoceanography of the region is now a subject of lively research (Gardner and Hemphill-Haley, 1986; Anderson et al.,1989; Lyle et al., 1992; Sancetta et al., 1992; Karlin et al., 1992; Prahl et al., 1995; Kennett and Ingram, 1995; Kennett et al., 1995). Much of the current research focuses upon the large temperature changes along the coast since the last glacial maximum and the possible formation in glacial intervals of a strong source of cold, oxygenated, intermediate waters.