The CCS consists of three distinct currents: (1) the California Current, flowing southward with a dispersed, eddy-ridden character that typifies eastern boundary surface currents (Hickey, 1979); (2) the subsurface California Countercurrent, flowing northward in a more focused manner than the diffuse, turbulent California Current, although little is known of its influence north of San Francisco (Hickey, 1979; Karlin, 1980); and (3) the surface Davidson Current, flowing northward along the coast north of Point Conception (~35°N), but only during fall and winter (Hickey, 1979). Some workers (e.g., Smith, 1992) have suggested that the Davidson Current may represent the surface manifestation of the California Countercurrent, and water property measurements seem to support this idea (Hickey, 1979). The onset of the Davidson Current during winter further suppresses upwelling along the northern California margin; otherwise, its oceanography is poorly understood.
On seasonal time scales, changes in the intensity and orientation of flow within the CCS reflect the influence of basinwide wind patterns (Fig. 2; Huyer, 1977, 1983). The strength of the gradient between the North Pacific high and the continental thermal low pressure system over California drives local surface winds, which blow weakly from the north, south of Mendocino (Huyer, 1983). These southward winds initiate Ekman transport in the surface layer, resulting in elevated sea-surface topography, depressed isopycnals in the gyre, and the upwelling of cool, saline, nutrient-rich waters along the coast (Huyer, 1983).
On interannual time
scales, changes in the CCS reflect the influence of ENSO events that originate
in the equatorial Pacific (Chelton, 1981). During El Niņo conditions, warmer
water propagates northward along the western margin of North America (Simpson,
1983; Emery and Hamilton, 1985; Johnson and O'Brien, 1990; Lyle et al., 1992;
Van Scoy and Druffel, 1993; Ramp et al., 1997). This warm-water intrusion
changes the overall density field of the surface water, reduces upwelling along
the coast of California, and results in lower sediment alkenone and marine Corg
concentrations. In fact, previous very high-resolution 
-SST
reconstructions show evidence of these subdecadal scale (3-5 yr) phenomena
(Kennedy and Brassell, 1992; Herbert et al., 1998). On the glacial-interglacial
time scales seen at Site 1020, the opposite scenario may exist, coupling warmest
-SST with
highest concentrations of alkenones in the sediments.
