California Current

# U.S. GLOBEC Poised to Study California Current Ecosystem

The physical and biological dynamics of the California Current System (CCS) 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 closely coupled to variations in physical forcing, thus sensitivity of the coupled physical-biological system to climate variability implies great sensitivity to climate change. U.S. GLOBEC has produced a Science Plan that suggests a number of hypotheses on how the coupled physical-biological system may respond to global climate change, and lays out a plan for how U.S. GLOBEC will study the CCS with the overall goal of producing predictions and integrated assessments of ecosystem response to climate change.

### The Research Program

GOAL: To understand the effects of climate change on the distribution, abundance and production of marine animal populations in the CCS.

APPROACH: To study the effects of past and present climate variability on marine animal populations and to use this information as a proxy for how the CCS may respond to future global warming and global climate change.

### Program Elements

- Provide a quantitative description of ecosystem dynamics and assess ecosystem response to climate variability in the CCS by developing, validating and applying regional models that couple ocean physical processes to biological proceses.

- Determine the modes of natural variability at seasonal-to-interannual-to-interdecadal time scales by conducting retrospective analysis of environmental, satellite, plankton, fisheries and paleoecological data sets from the California Current and other Eastern Boundary Current (EBC) systems.

- Examine climate variability and ocean and ecosystem responses, especially as it relates to El Nino--Southern Oscillation (ENSO) cycles by initiating long term monitoring and observation programs.

- Describe and compare interegional differences in mesoscale dynamics and life history strategies of key species to understand effects of El Nino/La Nina events on ecosystem structure using focused process-oriented field studies within the distinct regions of the CCS.

### Time and Space Scales

The CCS offers excellent venues for climate studies because the climate signals are strong and pervasive, and because regional differences are great. The U.S. GLOBEC research program will focus on variability at several scales:

- Seasonal-to-interannual variability in physical and biological dynamics;

- Decadal variability as related to possible regime shifts;

- Spatial variability along latitudinal and longitudinal gradients; and,

- Physical and ecological differences between the CCS and other Eastern Boundary Current ecosystems, to examine ecosystem response to differences in local, regional and basin scale forcing.

### Products

A successful program in the California Current System will produce the following:

- The development and/or significant improvement of a number of coupled biophysical models. These models will increase our ability to integrate biological and physical observations in coastal ecosystems in general and specifically in the CCS.

- The data sets assembled and collected during the program, including historical data sets, data from the mesoscale process studies and data from the monitoring activities.

- An improved monitoring system created during the program by augmenting existing systems with new elements.

- The experience gained by students and investigators in the use and interpretation of the combination of models and data. The training of students and other professionals in model use and interpretation is critical, if the activity begun during this program is to continue at the level necessary to reach the long-term goal.

The program in the California Current System will continue to move us toward our long-term goal of producing models that provide integrated assessments of the effect of environmental variability and climate change on ecosystems in the CCS and other marine ecosystems in coastal environments.

If the monitoring and field programs are designed correctly, the data sets collected should provide quantitative assessments of ecosystem structure during a period of five or more years that is likely to span a warm ENSO event. The connection to the larger basin scale variability will be provided by data collected in the tropical Pacific Ocean, e.g., that collected by the Tropical Ocean--Global Atmosphere (TOGA) and World Ocean Circulation Experiment (WOCE) programs. Within the CCS, the models will integrate the observations to provide a more complete picture of the biophysical interactions, while the data sets will continue to provide information useful in continued model validation and improvement. In this iterative fashion, the data sets and models will continue to increase our understanding of the way in which CCS ecosystems respond to large-scale environmental variability, long after the formal end of the program. The monitoring system should also continue to be useful in providing new information, as well as in ongoing model improvements. Some of the biophysical models will be imbedded within coupled ocean-atmosphere climate general circulation models (GCMs) in order to test their ability to reproduce the statistics of the historical and paleoecosystem time series, allowing further identification of model weaknesses and further model improvements. Along with the historical physical, zooplankton and fisheries data, they will permit a description of CCS dynamics and ecosystem response during several past ENSO cycles and the most recent interdecadal regime shift in the mid-1970Ős. When confidence in the biophysical models is established, they can also be imbedded within operational forecast models to provide short and medium range forecasts to the National Marine Fisheries Service (NMFS).

The models and monitoring systems will ultimately allow NOAA to provide managers and policy makers with better information on the role of environmental variability and climate change in determining abundances of living marine resources. Many marine populations in EBCs are especially vulnerable to collapse during El Nino events and other interannual to interdecadal extremes. The U.S. GLOBEC program will provide a more thorough scientific basis for assessments of the potential impact of El Ninos on living marine resources. In addition, the research will provide scientific information needed to analyze the economic impact of ENSOs on marine resources.

Information on the response of the system to decadal variability will also be valuable to managers. EBCs are known for their spectacular fishery collapses, such as the Monterey sardines (1940s) and the Peruvian anchoveta (1970s). Such collapses seem to be an inevitable consequence of inadequate understanding of the resources of the ecosystems. We need (1) improved resource management models based on understanding of qualitative state shifts; and, (2) improved capability to recognize and predict state shifts. It is doubtful that adverse fluctuations in the stocks and related industries can be avoided entirely, but if management were armed with the above knowledge and acted appropriately, it should be possible to reduce the severity and duration of the downturns and their resultant economic and social hardships.

In summary, the models, data sets and monitoring systems developed in this program will directly benefit society. The models will stimulate future scientific inquiries, and will identify the most important components of key ecosystems--those which most require close, continued observation. The models represent the ongoing, integrative element of the program. They are the important beginning of operational, climatic ecosystem modeling--the ultimate need of society in order to understand and manage such ecosystems. This will be the legacy of the U.S. GLOBEC program in the California Current System. (This article excerpted from the Executive Summary of U.S. GLOBEC Report No. 11, A Science Plan for the California Current)