Dr. Thomas Powell is conducting research under the aegis and funding of the U.S. Global Ocean Ecosystems Dynamics (U.S. GLOBEC) program, which is funded jointly by the National Science Foundation and National Oceanic and Atmospheric Coastal Ocean Program. U.S. GLOBEC scientists study the coupling between physical and biological processes in coastal marine ecosystems, using past and present climate variability as a proxy for future climate change. U.S. GLOBEC's approach is to integrate modeling, retrospective analysis of historical data, and process research to produce regional climate change scenarios and quantitative assessments of the sensitivity of selected marine ecosystems to climate variability and climate change. To date, U.S. GLOBEC has conducted studies in the Northwest Atlantic, Northeast Pacific, and Southern Ocean. Dr. Powell has a project (described more fully here) that uses numerical models to examine the interactions of physical variability on ecosystem processes and population dynamics of several key species in the California Current Ecosystem--one component of the Northeast Pacific Program. Dr. Powell also is funded within the U.S. GLOBEC Southern Ocean program, which is focusing on climate change/variability and ice-related processes on krill and their predators along the Antarctic Peninsula.

Northeast Pacific Program Background

Recent studies have documented that the physical and biological dynamics of the eastern Pacific are sensitive to natural climate variability on time scales ranging from seasonal to interdecadal, and spatial scales from local to basin-wide. Ecosystem structure is known to be closely coupled to variations in physical forcing, thus sensitivity of the coupled physical-biological system to climate variability implies great sensitivity to climate change.

To address questions about the physical and biological impacts of climate change requires data spanning long time horizons--from the past, present and future. Each of these is a component of U.S. GLOBEC studies: variability and change in the past is examined through Retrospective Data Analysis; conditions and biophysical interactions at present are examined through Process-Oriented Field Studies; and, documenting future variability and change is the rationale for instituting frequent, sustained Monitoring of the environment. Modeling and Synthesis activities will integrate the results from U.S. GLOBEC's process studies, monitoring, and retrospective activities, so that the consequences of climate change on the coastal marine ecosystem can be evaluated and projected. Research in our laboratory is directed to the modeling and synthesis activities within GLOBEC.

Our U.S. GLOBEC Northeast Pacific research project is a collaborative effort with Dr. Dale Haidvogel at Rutgers University and Dr. Hal Batchelder at Oregon State University. We use linked biophysical models to examine the interaction of circulation and individual behavior and energetics on the distribution and demography of zooplankton in the California Current. Eastern Boundary Current Systems, such as the California Current System (CCS), owe their high phytoplankton productivities to wind driven circulation patterns that bring nutrient-rich deep waters to the surface. These high rates of primary productivity are translated via high zooplankton secondary productivity, into high biomass of epipelagic fishes such as anchovies, hake, and salmon. Further, the spatial patterns of high primary and secondary productivity appear to be closely linked to mesoscale physical structures (e.g. filaments, jets, and eddies) in the CCS. We hypothesize that both spatial distribution and demographic processes (e.g. growth, fecundity, mortality) of calanoid copepods (e.g. Calanus pacificus and Metridia pacifica) and euphausiids (e.g. Euphausia pacifica), are influenced by circulation patterns within the CCS. We also hypothesize that the vertical migration behavior of these zooplankton interact with circulation fields in ways that significantly influence their spatial distribution and vital rates. Moreover, the bioenergetic and behavioral differences between species are hypothesized to influence differential population successes and spatial distributions.

We are using a series of linked physical/ecosystem/zooplankton models to study on seasonal and interannual time-scales the complex interaction of physical and biological processes (diel vertical migration and growth efficiency) in the CCS. We will emphasize major calanoid copepods (e.g., Calanus pacificus and Metridia pacifica) and euphausiid species (e.g., Euphausia pacifica and Thysanoessa spinifera) that represent critical linkages between primary production and salmon populations. In addition, we propose to further illuminate the roles of these processes through comparative studies with other ecosystems located within both similar and dissimilar dynamical environments.

By linking numerical models of physical circulation with concentration-based ecosystem models and an individual-based bioenergetics model of larger zooplankton (copepods and euphausiids) we intend to address the following questions:

• How does the circulation field impact the distribution and population success of major CCS zooplankton species such as C. pacificus, M. pacifica, E. pacifica, and T. spinifera?
  
  
• How do the behavioral and bioenergetic differences of these species interact with the circulation field, prey distribution and temperature to influence their relative population success?
  
  
• How does the interannual variability of the local environment (e.g., from large-scale atmospheric or oceanic fluctuations) modify these distributions and relative success of major CCS zooplankton species?
  
  
• How do physical and biological aspects of the CC/Zooplankton System compare to other well-studied ecosystems including those of particular interest to GLOBEC (e.g., Georges Bank, Gulf of Alaska, and Southern Ocean)?
  
  

The results of this research will include the developed ecosystem and zooplankton models, applied within regional and basin-scale circulation models. The coupled systems will be analyzed under seasonal and realistic surface forcing closely tied to CCS process studies. Furthermore, we will begin a comparative synthesis of physical and biological coupling within this and other well-studied GLOBEC ecosystems. The method we have chosen, coupling a bioenergetics individual-based model, that includes behavior, with a detailed physical circulation model is generally applicable to populations in other ocean ecosystems.