An F-Ratio Model for Pelagic Marine Ecosystem

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This research will develop a simple ecosystem model which will account for observed f ratios in pelagic marine ecosystems during both steady state and non steady state conditions. The central hypotheses of the model are as follows: (1) Production is controlled by a single nutrient, the identity of which is determined by the nutritional requirements of the phytoplankton community and the ratio of allochthonous nutrient inputs to the system. (2) The size spectrum of the phytoplankton community is a critical determinant of the f ratio. Large cells are associated with a high f ratio, and small cells are associated with a low f ratio. (3) Marine pelagic ecosystems naturally evolve toward a condition in which stability is maximized. Work carried out to date indicates that maximum stability is associated with low f ratios, i.e. in the range 0.05 0.1. Nutrient pulses are expected to shift the f ratio to larger values because under steady state conditions the large celled phytoplankton are always growing at a low relative growth rate, and the small celled phytoplankton are growing at a high relative growth rate. The principal long term goal of this research is the development of a simple model of the f ratio which can be embedded into much larger ocean-atmosphere models to explain the production and export of organic carbon from the euphotic zone. A secondary goal of this work is the development of a theoretical framework with which to reconcile various measures of the productivity and turnover of pelagic marine ecosystems, i.e., differences between gross photosynthesis and net photosynthetic production of particulate carbon.