## Executive Summary

U.S. GLOBEC's goal is to understand how physical processes influence marine ecosystem dynamics in order to predict the response of the ecosystem and the stability of its food web to climate change. A combination of field studies, model and technology development, and retrospective data analysis will be mounted to address this ambitious goal. U.S. GLOBEC will undertake a series of field programs over the next ten years to: 1) assess basic ecosystem characteristics including the natural variability of populations and their environments; 2) measure the rates of biological and physical processes; and, 3) characterize ecosystem sensitivity to climate forcing at regional to planetary scales. On the basis of these comparative studies U.S. GLOBEC will 1) determine critical global change variables; and, 2) design an operational ecosystem monitoring system that couples observations and modeling.

These field studies are coordinated with other activities: the development of coupled biological-physical models; retrospective analysis of data collected over the last century by oceanographers, climatologists and fisheries scientists; and, development of improved technology for making coupled observations of biology and physics. The vision of U.S. GLOBEC is that the models and scientific insights that arise from these field studies will ground an ecosystem monitoring program to predict variability in living marine resources. Accurate near-term forecasting of several important ecosystem properties (e.g., stratification, chlorophyll concentration, perhaps zooplankton biomass) in the sea is feasible, but can only be realized by an operational predictive system incorporating coupled biophysical models and judicious injection of standard monitoring data via data assimilation. Near-term predictive capacity is a prerequisite to predicting the long-term effects of global climate change.

U.S. GLOBEC has identified several ocean ecosystem types for emphasis. These include: banks, shelves and shallow seas; eastern boundary currents; the Southern Ocean; and critical regions of the open ocean. The first U.S. GLOBEC field study is occurring in the Northwest Atlantic on Georges Bank-the site of oceanographic and fisheries studies for more than a century and a region thought to be highly sensitive to climatic change. Eastern boundary current systems have strong biological and physical responses to climate forcing at interannual (e.g., ENSO events) to decadal (e.g., regime shifts) time scales. Global climate change is predicted to be greatest at high latitudes, with dominant effects being increased temperature and changes in ocean circulation. Fluctuations in the extent of sea-ice in the Southern Ocean may be the most dramatic manifestation of climate change in the Southern Hemisphere and may already be affected by changes in atmospheric greenhouse gas concentrations. The physical and biological environment in the open ocean differs dramatically from that found in coastal, polar, and marginal seas; so too may the coupling of physical and biological processes, and U.S. GLOBEC will investigate such differences.

The program is committed to modeling coupled physical and biological processes in the sea. Efforts to date have focused on incorporating basic ecological processes into regional scale transport models. More research is needed on refining the ecological aspects of these models, linking existing regional scale biophysical ecosystem models to ocean basin scale models, and assimilating biological and chemical data into interdisciplinary models.

Retrospective data analysis of fisheries, ecosystem, hydrographic and paleoecological data is crucial for expanding U.S. GLOBEC site-specific results to the larger scales that characterize the biogeographic distribution of populations and climate. From its inception U.S. GLOBEC has acknowledged that a program focused on coupling physical to biological processes in ocean ecosystems at local to global scales will be data limited. Existing data are often inadequate to answer the questions posed by U.S. GLOBEC-in part because the biological and physical data are collected over different time and space scales, and satisfactory coupling cannot be achieved. U.S. GLOBEC field studies will make efficient use of state-of-the-art technologies and methods, so that truly interdisciplinary data are collected.

U.S. GLOBEC will advance fundamental knowledge of ecosystem dynamics in the context of changing climate, and will provide input to research on, and management of, living marine resources. U.S. GLOBEC will help direct applied oceanographic and fisheries research towards the development of an observational network and data assimilative model system for monitoring and management. Such a system will provide the timely information base critical to informed decision making by environmental policy makers, economists, commercial leaders and resource managers.