Numerican modelling of the thermodynamics of Lake Baikal and the population dynamics of the Baikalian Diatom "Aulacoseira Baicalensis"

The prediction of the past climate from diatom ratios in Lake Baikal sediments will necessitate the understanding of the relationships between the diatom life-cycles and the physical processes occurring in the lake. To this end a diatom model is coupled to a three-dimensional general circulation model of Lake Baikal for the first time. The formulation of the diatom model and its parameterizations are described. The model is able to simulate the suspension of Aulacoseira baicalensis organisms in the photic zone by vertical dynamical processes. Populations are able to bloom under snow-free ice but are barely maintained under snow-free ice. A new three-dimensional model of Lake Baikal that can simulate the lake through the Summer and Autumn has been developed. The development of the model is documented with particular emphasis placed on the numerical scheme used for the advection of momentum and temperature, the thermal forcing of the model and the parameterization of the vertical eddy viscosity and vertical eddy diffusivity coefficients. The model simulations of Lake Baikal thermodynamics during the under-ice warming period in the Spring are in good agreement with the model of Lawrence et al. (2002). Model simulations of the temperature fields during the rest of the year are in good agreement with available observations. The model current velocities are similar to those reported by Shimaraev et al. (1994) but the lack of available wind field data prevents the simulation of a realistic circulation. This work highlights the need for further field studies of Lake Baikal and its diatom populations.