CS08 Biogeochemical Cycles
Date: Monday, June 10, 2002
Time: 4:15:00 PM
Location: Saanich
YoolA, Southampton Oceanography Centre, Southampton, United Kingdom, axy@soc.soton.ac.uk
Tyrrell, T, , Southampton Oceanography Centre, Southampton, United Kingdom, tt@soc.soton.ac.uk
Amongst phytoplankton the diatoms are strong competitors and contribute significantly to total global primary production. Aspects of their life history, notably their high sinking rates, make them important to the export flux of carbon into the ocean interior. However, unlike the majority of other phytoplankton, they require silicate to grow their cell walls and are controlled by its availability and distribution. Here a simple model is developed to study the relationship between the diatoms and the ocean's silicate cycle. The ecological component of this model pits the slightly superior diatoms against all other algae, with both groups competing for phosphate while the diatoms additionally require silicate. The model agrees reasonably with observed distributions of nutrients and with their biogeochemical fluxes. While theoretically superior, the diatoms are held in check by the availability of silicate, allowing the persistence and numerical dominance of the other algae. The concentrations of both nutrients are homeostatically controlled by the phytoplankton, and resist perturbations. Analysis finds that primary production in the model is ultimately controlled by phosphate, with silicate abundance controlling the fraction of the total produced by diatoms. However, results from a variant of the model find instead that the diatoms may exert control over total primary production in the ocean, and that their rise to ecological dominance in the last 65 million years may have been at the expense of ocean productivity.