History and future of coastal upwelling modes and biological responses in the California Current
Climate variability on multiple temporal scales is increasingly recognized as a major factor influencing the structure, functioning, and productivity of the California Current Ecosystem (CCE). Despite many long-term and integrative studies, a detailed understanding of climatic impacts on upwelling and biological processes is still lacking, compromising our ability to assess important concepts such as ecosystem "health" and "resilience". In this project sponsored by the National Science Foundation Biological Oceanography program, we tested the hypothesis that seasonal upwelling modes are forced by contrasting atmospheric-oceanographic processes, exhibit different patterns of low- and high-frequency variability, and will be differentially impacted by global climate change, with corresponding impacts on biology. To address this hypothesis we took a three-tiered approach focusing on the past, present, and future of upwelling in the CCE. First, for the past, tree-ring data co-varies with fish growth and seabird reproductive success and all are similarly sensitive to a driver of winter upwelling, the Northern Oscillation Index (NOI). Therefore, we used tree rings to reconstruct winter climate variability. Our reconstruction indicates that variability in upwelling has increased over the instrumental record, but nonetheless remains within the range of natural variability (Black et al. 2014; Bryan Black, University of Texas).
Second, for the present, we examined the responses of a suite of species to seasonal modes of upwelling, including Pacific sardine (recruitment), black rockfish (growth), rhinoceros auklet and Brandt's cormorant (survival), and coho salmon (survival). To conduct this work, we integrated winds and temperatures from local buoy data to better capture climate variability on finer timescales than we had in the past (Garcia-Reyes et al. 2013). Third, for the future, we investigated seasonal upwelling modes in relation to various climate-change scenarios using IPCC-class global climate models (GCM; Ryan Rykaczewski, University of South Carolina, Program for Climate Model Diagnosis and Intercomparison).
Overall, this study is of significance because it provided information about the past variability, current causal forces, and potential future changes in upwelling as well as its biological consequences in the California Current. In addition to the basic intellectual merits of our study, we have contributed results to state, national, and international policy-makers, including the IPCC's Assessment Report 5 (AR5), Chapter 30.