Abstract:
A regional set of marine cores now exists to study the evolution of ocean surface temperatures and other paleoclimatic signals along the west coast of North America. Core locations range from Vancouver Island to the north, to the tip of Baja California to the south. We report on the evolution of sea surface temperatures (SST) and marine productivity, as recorded by alkenones. Several sites also have pollen records, allowing us to compare marine and terrestrial responses. We find that surface climate signals covary tightly with global climate, as represented by benthic d18O, through 80% of a typical glacial-interglacial cycle. However, the associations between SST and ice volume break into three regional patterns during glacial maxima and terminations. North of Point Conception (heart of the California Current), SST patterns are very similar to benthic d18O and to Greenland ice core surface temperature data (ODP Site 1019). The abundance of redwood pollen very closely follows SST in this northern province. In the California borderland region, warmings begin during peak glacial conditions, and significantly precede the deglacial sea level rise. Off Baja California, SST follows benthic d18O, but without the high frequency oscillations of temperature observed in Greenland. These changes outline regional reorganizations of surface winds and currents during times of maximum ice volume. Our data suggests that the geographic extent and intensity of the California Current system was much reduced during glacial maxima in comparison to modern conditions. Furthermore, the regional patterns in ocean temperature change that we observe caution against matching terrestrial records directly to ice volume, a mistake that we believe has been made in interpreting the Devils Hole calcite record.