An Eulerian Model of Phytoplankton Photosynthetic Response in the Upper Mixed Layer
We combined an Eulerian model of an upper mixed layer forced by dynamic and convective processes with a responsive photoadaptation model of photosynthesis. Incident radiation was divided into photosynthetically active and inactive components. The model was initialized to simulate physical conditions in Lake Titicaca on August 12, 1982, but it applies equally well to oceanic conditions. The simulation provides the time course of water column temperature, phytoplankton photoinhibition, and relative carbon fixation of phytoplankton as depth contours for comparison with the field data. The predicted and observed temperature profiles generally agree; diurnal changes in specific humidity are required to more accurately specify heat loss. The predicted photoinhibition resembles the observed photosynthetic state of the natural community based on fluorescence, but the modeled recovery from photoinhibition is too rapid. This discrepancy also affects the comparison between predicted and observed bottle determination of carbon fixation. The biological formulations in the model provide approximate fits to field observations, but improved realism requires a biological initialization that is more specific to the natural phytoplankton community.