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

该项目的主要目标是重建过去500至2000年间加州海流和阿拉斯加湾北部系统的鲑鱼丰度趋势，比较不同系统之间的鲑鱼丰度趋势，并确定气候变化与鲑鱼丰度之间的关系。该项目将使用新开发的技术，从湖泊沉积物岩心的稳定同位素分析中重建鲑鱼丰度趋势。将对加州海流系统和阿拉斯加湾北部系统中的几个地点进行研究，以比较区域内和区域之间的趋势。鲑鱼丰度的记录将与通过研究树木年轮、冰川推进和其他来源确定的古气候数据进行比较。通过分析沉积物岩心中的稳定氮同位素，将重建鲑鱼丰度的长期记录。氮稳定同位素的这一新应用是基于观察到太平洋鲑鱼在返回产卵时向淡水系统提供可测量数量的元素。相对于陆源氮，来自成鱼的氮在15N中富含，因此，过去回归成鱼数量的变化反映在沉积三角洲15N的下部变化中。硫的稳定同位素也有可能将鲑鱼衍生的元素追踪到淡水生态系统中，因为海洋和陆地的Delta34S特征有很大的差异。由于N和S有不同的地球化学控制和不同的地球化学循环过程，这两种示踪剂的使用应该会导致鲑鱼丰度的强劲重建。

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.