Paleogeochemical and oxygenation history of the Eastern Pacific Ocean

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The western continental slopes of North and South America are bathed at intermediate water depths by large pools of oxygen-poor water that are thought to play a significant role in global climate modulation by limiting the nitrate content of the world's oceans. Because nitrate is a key nutrient for phytoplankton, its biochemically-mediated loss from the low oxygen water constrains the productivity of the sea. We have been investigating controls, both biological and physical, on the intensity of such oxygen depletion through time, focusing on the NE subtropical and subarctic Pacific. We propose to expand this work through a focus on several of 22 giant-piston cores raised from the western margin of North America in 2002. Cores from the Vancouver Island, Oregon, and northern California margins, as well as the Gulf of California are the initial targets in this project.  Our objective is to reconstruct marine production and intermediate water circulation across a broad swath of the North Pacific over the last 100,000 or so years. The research includes a focus on the distribution of silver in continental margin sediments. Our new data show that the sedimentary silver content increases with water depth, while water-column measurements we have made indicate scavenging of silver from solution in upper North Pacific intermediate waters. These phenomena--for which no explanations currently exist--will receive particular attention in the proposed research. Finally, we shall explore the history of productivity in the Galapagos Archipelago and its link to El Niño over the last 10,000-20,000 years through intensive study of a sediment core to be collected during a research cruise to the eastern equatorial Pacific proposed for 2007. We anticipate that this research program will contribute to an improved understanding of both climate history and oceanographic processes that influence and respond to climate changes on Earth.