The Columbia River Plume is a highly dynamic water mass that supplies silicate and trace metals, fresh
water, and dissolved and particulate organic matter to the Oregon/Washington shelf. The optical and physical
properties of the river plume evolve as it travels away from the river mouth and undergoes both aging and
dilution by surrounding waters. The objectives of this study were to (1) identify initial optical properties of
fresh plume waters at the river mouth, (2) track changes in the optical signature of the water mass as it
advects seaward from the mouth, and (3) predict residence time of the water mass on the shelf from changes
in the optical signature, using remote sensing data. These results are compared to central California, where
river plumes are much more episodic and spatially smaller, to determine the limits of detection using standard
(1 km) and high-resolution (250 m) data from the MODIS platform.
Under most conditions nitrate uptake is light-dependent and may be characterized using the same uptake-irradiance response parameters as carbon. This suggests that the quantum yield of nitrate may be determined, which in turn allows for the determination of new production using existing quantum-based models of primary production. Balanced growth conditions are rare in upwelling phytoplankton assemblages, which makes it difficult to gauge new production from primary production. During the spring of 1995, a multi-investigator initiative was carried out to assess the role of biology in the air-sea exchange of carbon dioxide in coastal Central California. During the upwelling season this region is highly variable in space and time and provides the opportunity to study phytoplankton exhibiting a variety of physiological states and occurring in a variety of environmental milieus. Measured bio-optical parameters demonstrated no correlation to the corresponding environmental characteristics, and comparison of the calculated quantum yields demonstrated that phytoplankton carbon and nitrogen metabolic processes were not in a balanced state, as would be expected. Determination of new production rates using a simple bio-optical model was in good agreement with traditional estimates of new production using <SUP>15</SUP>N incubations.