Origin and Hemispheric Linkage of Millennial-Scale Climate Variability in the Pacific

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This award will assess various mechanisms thought to be responsible for millennial-scale variability in surface and shallow subsurface water masses in high-sedimentation rate cores from the eastern margin of the Pacific over the past ~65,000 years. Three key regions were chosen for detailed study in the Northeast Pacific, Equatorial Pacific, and Southeast Pacific, because they offer an opportunity to test three hypotheses that might affect patterns of climate variability derived from coupled atmosphere-ocean model studies.The first hypothesis assumes that sea-surface temperature anomalies are transmitted rapidly from the North Atlantic to the North Pacific via the atmosphere. This implies a strong response in the North Pacific and little or no response in the south.The second hypothesis assumes that global temperature anomalies propagate slowly in response to changes in thermohaline circulation and predicts large changes in intermediate water temperatures and ventilation in the Southeast Pacific that are shifted in phase relative to changes in the northern hemisphere.The third hypothesis assumes that rapid climate oscillations originate in the tropical Pacific via El Nino-Southern Oscillation (ENSO) type mechanisms with attendant effects on the ocean and atmosphere. This implies major changes in sea-surface temperatures (SST) and pycnocline structure in the eastern tropical Pacific and transmission of energy poleward into both hemispheres along the eastern margin. The researchers expect, based on a careful selection of sampling sites and the application of high-resolution paleoclimatic proxies, to establish the spatial "fingerprint" of millennial-scale variability in the Eastern Pacific. This is important because it will help resolve the primary mechanisms responsible for millennial-scale changes in the region especially the linkage between the hemispheres and the interaction between tropical and extratropical climate variability.