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). Yet, despite many long-term and integrative studies, a detailed understanding of climatic impacts on upwelling and biological processes is still lacking, compromising our abilities to assess important concepts such as ecosystem "health" and "resilience." To address these issues in the central-northern CCE, the PIs have recently collated and analyzed records of rockfish and salmon growth and seabird reproductive success with respect to upwelling variability (NSF award #0929017). These diverse, multi-decadal time series revealed the importance of wintertime upwelling on ecosystem structure and function, even though upwelling, a principal driver of productivity in the CCE, is largely a summertime process. This research led to an unexpected discovery that winter and summer upwelling vary independently of one another in distinct seasonal "modes", with some biological processes affected by the winter mode and others by the summer mode. This is of significance because the summer mode shows a long-term increase (despite inter-decadal variability) while the winter mode does not.
Intellectual Merit: In this new project, the PIs will test the overarching hypothesis that upwelling modes are forced by contrasting atmospheric-oceanographic processes, exhibit contrasting 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 the PIs propose a three-tiered approach to better understand seasonal upwelling modes and their differential impacts on biology of the CCE. First, they will examine the responses of an entirely new suite of species to upwelling modes, including Pacific sardine (recruitment), black rockfish (growth), rhinoceros auklet and Brandt's cormorant (survival), and coho salmon (survival). Previously, coarsely resolved upwelling indices were used in these analyses, but the PIs now will integrate winds and temperatures from local buoy data to better capture climate variability on finer timescales. Second, they will derive a more mechanistic understanding of seasonal upwelling modes and use this information in combination with global climate models to forecast upwelling responses under various climate-change scenarios. Third, preliminary results indicate that tree-ring data co-vary with the fish and seabirds and are similarly sensitive to a driver of winter upwelling, the Northern Oscillation Index (NOI). The PIs will use tree-ring data to provide a 300-400 year reconstruction of the winter NOI to assess the historical range of variability in upwelling mean and variance. This study will reveal the past, present forcing, and potential future of upwelling and its biological consequences in the California Current.
Broader Impacts: This study will explore the history, future, and biological impacts of independent, seasonal climate modes and their impacts on key species. In so doing, the PIs will develop an understanding of coupled climate-ecosystem change that will be contributed to state, national, and international policy-makers, including the California Cooperative Climate Adaptation Team (CO-CAT)and the IPCC Assessment Report 5. The PIs will develop and test biological and physical indicators of California Current ecosystem productivity and will make this information available for management, specifically fisheries stock and integrated ecosystem assessments. The project will provide cross-training for 2 post-doctoral research associates, 2 other young scientists, and 1 undergraduate in physical oceanography, marine ecology, quantitative skills, communication, as well as the business of science, such as project and fiscal management and fund-raising.
BA Black, WJ Sydeman, and SJ Bograd Climate variability is increasingly recognized as a major influence on the structure, functioning, and productivity of the California Current Ecosystem (CCE). Yet despite many long-term and integrative studies, a detailed understanding of climatic impacts on upwelling and biological processes is still lacking, compromising our abilities to assess important concepts such as ecosystem "health" and "resilience". To address these issues in the central-northern CCE, we have recently collated and analyzed records of rockfish and salmon growth and seabird reproductive success with respect to upwelling variability (NSF award #0929017). These diverse, multi-decadal indicators revealed the importance of wintertime upwelling on ecosystem structure and function, even though upwelling, a principal driver of productivity in the CCE, is largely a summertime process. This research led to an unexpected discovery that winter and summer upwelling vary independently of one another in distinct seasonal "modes", with some biological processes affected by the winter mode and others affected by the summer mode. This is of significance because the summer mode shows a long-term increase (despite inter-decadal variability) while the winter mode does not. In this current project, we have tested the overarching hypothesis that upwelling modes are forced by contrasting atmospheric-oceanographic processes, exhibit contrasting 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 take a three-tiered approach: Employ a suite of temperature and wind data to better describe seasonal CCE climate modes, then compile a broad dataset of growth, survival, and recruitment data to better establish their biological importance. Demonstrate that the same broad-scale atmospheric conditions that drive wintertime upwelling also drive wintertime precipitation in coastal forests, then use tree-ring data to hind-cast wintertime climate over the past several centuries to describe historical ranges of variability. Derive a more mechanistic understanding of seasonal upwelling modes and use this information in combination with global climate models to project upwelling responses under various climate-change scenarios. Outcomes for each of these objectives are: Multivariate indicators of upwelling and species’ responses were developed using wind and sea surface temperature (SST) data as well as growth and reproductive data for 11 species of fish and seabirds. From previous work, we predicted that winds and SST from nearshore buoys could be decomposed into winter and spring/summer ‘modes’ of variability, but only a single mode of "winter/spring" environmental variability was observed. We attribute this difference from expectations to the local and shorter-term measurements of winds and SST used in this study. Most species responded to winds and SST variability similarly, but SST was a better predictor of most biological responses. We found that broad-scale, wintertime high pressure systems over the northeast Pacific synchronize growth in marine and terrestrial ecosystems by affecting upwelling intensity in the ocean and precipitation over land. Thus, tree-ring data could be used to hind-cast wintertime climate over the past six centuries. In so doing, we find that the climate pattern is dominated by high-frequency variability, but that the 20th century is characterized by unusually strong climate anomalies that can severely reduce CCE productivity. Three approaches were taken to address Goal 3: We analyzed atmospheric pressure data in each of the world’s major coastal upwelling zones and show that variability in upwelling-favorable winds is dominated by oceanic high pressure systems (OH), particularly in winter, and only weakly influenced by continental thermal low systems during the summer. This work underscores the importance of OH systems to upwelling winds. In a meta-analysis of the published literature, we find that upwelling-favorable winds have significantly intensified in four out of five coastal upwelling zones. The strongest intensification signals occurred during the warm season and at higher latitudes, consistent with patterns of global warming. We analyze output from general circulation models, which suggest that projected changes in the magnitude of upwelling over the next century are relatively weak. However, the various models indicate a decline in summertime upwelling-favorable winds, especially in the southern CCE. We suspect that these changes are related to the poleward migrations of major atmospheric pressure cells that drive upwelling winds. Overall, this study used observational records to investigate atmospheric forcing mechanisms for the winter and summer climate modes as well as establish biological response, hind-cast the winter mode using tree-ring data to asses historical ranges of variability and use coupled atmosphere-ocean global circulation models to project the potential future of upwelling and its biological consequences. In so doing, we have published 4 peer-reviewed papers, provided 18 talks at scientific conferences or research centers, taught 2 workshops, and trained two undergraduate interns and a post-doctoral researcher in "ecosystem oceanography."
