Hofmann¹, Eileen E., Marjorie A. Friedrichs², J. Christian³, W. Wang⁴, R. Murtugudde⁴ and Antonio J. Busalacchi⁴

¹Center for Coastal Physical Oceanography, Crittenton Hall, Old Dominion University, Norfolk, VA 23529, Tel: 757-683-5334, Fax: 757-683-5550, E-mail: hofmann@ccpo.odu.edu, ²Center for Coastal Physical Oceanography, Crittenton Hall, Old Dominion University, Norfolk, VA 23529, ³Canadian Centre for Climate Modelling and Analysis, University of Victoria, P.O. Box 1700 STN CSC, Victoria, BC, V8W 2Y2 Canada and ⁴Earth System Science Interdisciplinary Center, 2207 Computer and Space Sciences Building, University of Maryland, College Park, MD 20742

Comparison of model-derived phytoplankton distributions with SeaWiFS data at two sites in the equatorial Pacific Ocean

SeaWiFS observations for 2º by 2º regions, centered around 140ºW and 165ºE, were obtained for 1998 to 2002, which includes a strong El Niño-La Niña period. The SeaWiFS data were compared with simulated plankton and nutrient distributions for the same period obtained from a multi-component lower trophic level ecosystem model developed for the equatorial Pacific. The results of the comparisons indicate that the model accurately simulates the dynamics governing chlorophyll distributions at 140ºW, but underestimates chlorophyll variability and concentrations at 165ºE by more than 50%. This difference at 165ºE reflects strong grazer control at this location in the model-derived fields. Such a strong top-down control is not suggested by the available in situ data sets. These results indicate research directions associated with model structure and parameterizations that need addressing for application of ecosystem models to basin-scale systems. Suggestions are made for alternative grazing parameterizations that relate biological and physical dynamics over large areas. These results also indicate the usefulness of ocean color data sets for validating model dynamics, as well as model-derived distributions.