The oceanographic and climate histories of the eastern and western equatorial Pacific (Ocean Drilling Program [ODP] Legs 138 and 130, respectively) and the high-latitude North Pacific (ODP Leg 145) have already been explored with scientific drilling, but sediments reflecting the history of the California Current and the temperate North Pacific, the oceanographic link between the two regions, had not previously been recovered using modern drilling techniques. ODP Leg 167 represents the first time since 1978 that the North American Pacific margin was drilled to study ocean history (Fig. 1). The leg shipboard scientific party collected not only high-resolution records within the Pleistocene through Pliocene but also lower resolution records since the middle Miocene. Sites were drilled to collect sediments needed to study the links between the evolution of North Pacific climate and the development of the California Current system.
The California Current system is probably the best investigated eastern boundary current system in the world. Nevertheless, the response of the California Current system and associated coastal upwelling systems to climate change is poorly documented. During Leg 167, 13 sites were drilled—Sites 1010 through 1022—along the climatically sensitive California margin (Fig. 1). These sites are arrayed in a series of depth and latitudinal transects to reconstruct the Neogene history of deep, intermediate, and surface ocean circulation and to understand the paleoceanographic and paleoclimatic history of this region (Table 1).
Biostratigraphic research objectives for the California margin sites focus on a few major threads. These are (1) documenting the record of surface ocean processes in the northeastern Pacific, (2) investigating the longer term linkage between the oceanographic evolution of the northeastern Pacific and continental records of marine and terrestrial processes, and (3) defining accurate depth and age frameworks for all sites. The sediments collected on Leg 167 provide one of the first direct opportunities to enhance current biostratigraphies and biochronologies to improve the temporal framework for refined paleoceanographic analysis.
Extensive Miocene to Pleistocene diatom records were recovered at several sites. The purpose of this paper is (1) to document the diatom stratigraphy at each site, (2) to test the utility of diatom datum levels in relation to the magnetostratigraphy, and (3) to present a diatom zonation for the middle Miocene through Quaternary. Because the paleomagnetic calibration of early Miocene through Pleistocene diatom datum levels in the North Pacific is generally completed (Koizumi and Tanimura, 1985; Barron and Gladenkov, 1995; Yanagisawa and Akiba, 1998), the emphasis is laid upon the testing the isochroneity of diatom datum levels in the northeastern Pacific sediments.