Millennial scale climate variability of the northeast Pacific Ocean and northwest North America based on radiolaria and pollen

Abstract

Radiolaria and pollen abundances in marine sediment cores from the northeast Pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle (0–150 kyr). These data allow direct comparison of the climate response of continental and oceanic systems. Detailed δ 18O and AMS- 14C measurements provide a link into global stratigraphic frameworks. Canonical correlation analysis extracts two modes of variation common to both the Radiolaria and pollen records. The first mode of variation correlates an assemblage of Radiolaria associated with coastal upwelling with increased redwood, western hemlock, and alder pollen. This association is consistent with the modern relationship between coastal upwelling, coastal fog and redwood forests. A second canonical mode relates an oceanic fauna now found in highest abundance in the far North Pacific with reduced pine and western hemlock pollen abundance. Comparison of these records to an ice core δ 18O record suggests that at wavelengths >3000 years, warm events in Greenland are correlated to intervals of increased coastal upwelling off Oregon, decreases in importance of very cold North Pacific fauna (suggesting warming), and increases in pollen associated with wetter coastal environments. Radiolarian based sea-surface temperature estimates suggest that the variability of the northeast Pacific on this time scale is about 2°C. Warming in the coastal regions reflects reduced advection of the California Current, but is moderated by increases in cool coastal upwelling. We infer that the response of the northeast Pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid- to high latitudes. Preliminary analysis suggests that oceanic variability off Oregon at wavelengths <3000 years is similar to the Dansgaard–Oeschger cycles of the ice core δ 18O records. This variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements. This finding suggests that, unlike longer-period millennial scale events, the propagation of the shorter wavelength events to the Northeast Pacific is through subtropical or tropical teleconnections.