Ecosystem Predictions with Approximate vs. Exact Light Fields

: Ten-year simulations were performed using a coupled physical-biological-optical ocean ecosystem model with both simple analytic and accurate EcoLight numerical computations of the in-water irradiances. The predicted chlorophyll concentrations differed by tens of percent over the course of 10-year simulations. The EcoLight code runs with less than a 30% increase in nm time, which providing several advantages than cannot he obtained with an analytic light model. These advantages are as follows. (1) EcoLight does a much better job of computing irradiances near 400 and beyond 600 nm, and at depth. These differences can have significant effects on how particular phytoplankton functional groups evolve in time and at depth. (2) EcoLight can model any water body, including Case 2 water and optically shallow waters for which bottom reflectance can substantially increase the irradiance available for photosynthesis and water heating. (3) EcoLight provides the outputs necessary for ecosystem validation using satellite-derived water-leaving radiances or remote-sensing reflectances, without the necessity of using a chlorophyll algorithm to convert satellite data into an ecosystem variable. (4) EcoLight provides a means for improved ecosystem model initialization and data assimilation directly in terms of the available data, again without an intermediate step involving a data-to-chlorophyll conversion algorithm.