An Eulerian model of phytoplankton photosynthetic response in the upper mixed layer

Abstract

An Eulenan model of an upper mixed layer forced by dynamic and convective processes is combined with a temporally responsive photoadaptation model of photosynthesis. Incident radiation is divided into photosyntheticalJy active and inactive components to distinguish between biological and physical forcing. The physical model is initialized to simulate conditions in Lake Titicaca on August 12, 1982 Model output provides the time course of water column temperature, phytoplankton photoinhibition and relative phytoplankton carbon fixation as depth contours for comparison with published observations. 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 determinations of carbon fixation. The basic formulations in the model provide approximate fits to field observations. If more complete information on physical and biological initializations and on temporal forcing were available, the basic formulations could be refined