Understanding the causes and manifestations of biological variability over long time scales remains a critical and elusive goal for ecosystem ecology. In the Northeast Pacific, long-term variation in atmosphere-ocean coupling appears to have organized biological production into a series of distinct interdecadal regimes during the last century. For instance, up to three-fold changes in salmon fishery catches in the Alaska Current were coindicent with shifts between interdecadal climate regimes. Despite this enormous temporal variability in fish population dynamics, we have only a weak understanding of the long-term climatic drivers that control biological productivity in this vast and important ecosystem. A key hypothesis proposes that the main drivers of biological change in the Northeast Pacific involve the interactive effects of pan-Pacific, bi-decadal and penta-decadal climate oscillations. Historical records of biological productivity prior to the 20th century have not been established for the Alaskan Current domain of the Northeast Pacific; their absence represents a major impediment towards understanding the temporal organization of biological productivity in this ecosystem. Here, the investigators propose to quantify the fundamental modes and magnitude of interdecadal variability in sockeye salmon populations of the Alaska Current during the last 500 years, to improve our understanding of the critical sources of temporal organization in the Northeast Pacific.
These scientists will use paleoecology to characterize the long-term patterns of biological variability in the Alaskan Current domain of the Northeast Pacific. Specifically, they will infer historical changes in populations of sockeye salmon (Oncorhynchus nerka) by tracking variation of a natural geochemical tracer (15N) that accumulates in the sediments of spawning lakes in proportion to salmon density. High resolution dating of sedimentary sequences will be accomplished through detailed radio-isotope analyses of sediments and by identifying volcanic ash layers with known ages. Existing 35-to-100 year long historical records of salmon population dynamics, climatic conditions, and lake production will enable them to calibrate sedimentary chronologies of geochemical and biological markers. They will also use carbon stable isotopes and fossil algal pigments from sediments to quantify the impact of salmon-derived nutrients on lake productivity. They will use spectral analysis and temporal domain time-series models to quantify the frequency, duration, and magnitude of historical shifts in fish production, and how these relate to independent proxies of paleoclimatic conditions. They will then apply the time-series models developed from sedimentary and other existing paleoclimate records to forecast future changes in the biological productivity of the Northeast Pacific for the next century.
This synthesis of new and existing data will provide a high-resolution, concrete description of the long-term variability in the biological productivity of the Alaska Current domain of the Northeast Pacific. They will test the hypothesis that the biological productivity within this oceanic domain has been synchronized by inter-decadal climate regimes associated with bidecadal and pentadecadal climate oscillations. These data will provide the information needed to investigate the spatial and temporal coupling of biological productivity to climate oscillations throughout the Northeast Pacific. In particular, our work will provide the data needed to test the hypothesis that biological productivity in the Alaska and California current domains of the Northeast Pacific respond synchronously, but out of phase, to interdecadal climatic forcing. The synthesis of historical- and paleo-indicators of oceanic conditions, climatic conditions, and biological productivity will place the recent century of ecosystem dynamics in a substantially longer temporal context than is currently available. This knowledge will provide a scientific basis for adapting management to the time scales relevant to the coastal marine, freshwater and riparian ecosystems of the Northeast Pacific.
