Light in the surface ocean is necessary for photosynthesis by marine algae. It is also a major source of heating. Visible light diminishes approximately exponentially with increasing depth in the upper ocean. In most of the current generation of Earth System Models used for climate projection, the vertical profile of in-water shortwave radiation is calculated as an exponentially decaying function where the attenuation coefficient is parameterized in terms of phytoplankton photosynthetic pigment (chlorophyll-a) concentration. In doing so, the attenuation of light by all other aquatic constituents is assumed to co-vary with chlorophyll-a concentration. The work in this dissertation presents a revised parameterization for the light attenuation coefficient that varies as a function of chlorophyll-a concentration and the light absorption coefficient for colored detrital matter (CDM). By separating the contribution by CDM, it is free to vary independently. Two ESM model runs were conducted: the experimental run, where the light attenuation coefficient was calculated as a function of both chlorophyll-a concentration and light absorption by CDM and the control run, where the light attenuation coefficient was calculated as a function of chlorophyll-a concentration only. The geographical distribution of light absorption by CDM was prescribed using an ocean color satellite data product using data retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua Earth-observing satellite. The difference between the results of these two model runs showed increased light attenuation by CDM decreased total ocean biological productivity, increased wintertime ice formation and resulted in more extreme sea surface temperatures compared to the control run. These studies are the first global-scale investigations of the biological and hydrodynamic impacts of optical attenuation by CDM in an Earth System Model. They demonstrate the importance of accurately representing light attenuation by independently varying aquatic constituents
