A HIGH RESOLUTION BIO-OPTICAL MODEL OF MICROALGAL GROWTH: TESTS USING SEA-ICE ALGAL COMMUNITY TIME-SERIES DATA

A high resolution, two-dimensional (z, t) time-dependent model of microalgal growth has been developed in which simulated physiological responses are determined by ambient temperature, spectral irradiance, nutrient concentration, and salinity. The model is based on the concept of a maximum temperature-dependent growth rate that is subsequently reduced by limitations imposed from insufficient light or nutrients, as well as sub- or supraoptimal salinity. Limitation terms for these variables are derived from studies of nutrient-, light-, and salinity-dependent algal growth (or photosynthetic) rates that have been normalized to maximum observed rates with respect to each variable. Particular emphasis was placed on developing the formulation for light limitation, which includes the effects of diel changes in spectral irradiance, seasonal changes in photoperiod, and related adjustments in biochemical C: Chl a ratios. This level of detail was needed because the importance of light limitation has been demonstrated on diurnal, seasonal, and annual time scales in polar regions. The model was tested by comparing simulation results to a sea-ice microalgal bloom in McMurdo Sound, Antarctica, in 1982. Environmental information from 1982 and biological coefficients derived from sea-ice communities were used as model input. Model results showed excellent agreement with microalgal bloom dynamics observed in 1982 under a variety of environmental conditions. Predicted Chl a standing crops were consistently within 15% of observations for the congelation ice and platelet ice, regardless of snow thickness (snow-free, 5-cm, and 10-cm snow-cover scenarios were tested), and predicted vertical distributions of Chl a exhibited the same depth-dependent pattern as observations.