Abstract: Understanding how global ecosystems are changing and how they respond to and affect global environmental change and the carbon cycle are key goals presented in NASA NRA-01-OES-04. To contribute to these objectives, we propose field studies to determine the importance of iron availability as an influence on ecosystem structure and productivity in the Southern California Bight, the location of the California Cooperative Oceanic Fisheries Investigations (CalCOFI) program, one of the longest and most comprehensive time series of marine observations in the world. The CalCOFI program has made fundamental contributions to our understanding of large-scale environmental change, and in-situ optical measurements carried out through the CalCOFI program to support the validation of ocean color satellite algorithms constitute approximately 20% of NASA's ocean color satellite database. We hypothesize that iron supply is a significant, interannually variable, and previously uncharacterized factor in phytoplankton growth in some areas of the CalCOFI sampling region, particularly coastal areas at times when the nitricline shoals significantly. To test this hypothesis we propose to measure iron concentration and speciation and to conduct iron-addition incubation experiments on a series of CalCOFI cruises covering several annual cycles in productivity. Our studies of iron availability will be correlated with studies of bio-optical variability and analysis of SeaWiFS and other ocean color satellite data for the CalCOFI region. The proposed research will enhance the continuing value of the CalCOFI program for studies of environmental change and for validation of ocean color satellite measurements, by increasing our understanding of the forcings that influence community structure and phytoplankton productivity in the system. In addition, this proposal outlines an educational plan to highlight the role of trace metals in the global carbon cycle and the use of remote sensing data in identifying causal relationships between nutrient supply and oceanic primary productivity.