An important issue in modeling and predicting upper ocean variability is the nature of the interactions between ocean biology, ocean dynamics, and irradiance penetration. Numerous studies using in situ observations and model simulations to investigate the effects of biota on light penetration have demonstrated that this biological-physical feedback may be significant over a wide range of spatial and temporal scales. Using a general circulation model which takes into account interannual variations in surface chlorophyll for the period September 1997 to May 2003, we investigate the effect of varying chlorophyll concentration on surface temperature. We conclude that, by using climatological monthly mean chlorophyll values, we capture the first-order effect of chlorophyll on light penetration.