GLOBEC Northeast Pacific Retrospective Study: Long-Term Variability in Salmon Abundance in the Gulf of Alaska and California Current Systems

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PROJECT SUMMARY The main goals of this project are to reconstruct trends in salmon abundance in the California Current and Northern Gulf of Alaska systems over the past 500 to 2000 years, to compare trends in abundance between the systems, and to determine relationships between climate change and salmon abundance. This project will use newly developed techniques to reconstruct salmon abundance trends from stable isotopic analysis of lake sediment cores. Several sites will be studied in each of the California Current and Northern Gulf of Alaska systems to compare trends within and between regions. The records of salmon abundance will be compared with paleoclimatic data determined from studies of tree rings, glacial advances and other sources. Long-term records of salmon abundance will be reconstructed by analyses of stable nitrogen isotopes in sediment cores. This new application of N stable isotopes is based on the observation that Pacific salmon supply measurable quantities of elements into freshwater systems when they return to spawn. Nitrogen derived from adult salmon is enriched in 15N relative to terrestrially-derived N. and thus past changes in the number of returning adult salmon are reflected by downcore changes in sedimentary delta15N. The stable isotopes of sulfur also have potential to trace salmon-derived elements into freshwater ecosystems, because there is a large difference between marine and terrestrial signatures of delta34S. Because N and S have different geochemical controls and different geochemical cycling processes, the use of both tracers should lead to a robust reconstruction of salmon abundance.