Gieschen, Lena (2008) Impact of different grazing functions on simulated biological production at selected ocean sites. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 78 pp.

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Abstract

A model study is presented in which, in an NPZD plankton model, a detailed phytoplankton formulation is combined with various zooplankton grazing terms. Plankton models are sensitive to the grazing formulation, and this approach allows for systematic investigation of their respective impact on overall model performance. The plankton model is coupled to a onedimensional physical model, and modelled annual cycles of surface nitrate and vertically integrated chlorophyll are compared to observations from three different ocean time-series stations that each represent different regimes. A model setup is developed that simulates the characteristic annual cycles of a bloom station in the North Atlantic and of an HNLC station in the subarctic Pacific, as well as those of an oligotrophic gyre, with one single parameter set. The role of iron is not taken into account and the results show that the absence of a bloom and the corresponding high nitrate concentrations can be explained by strong grazing pressure. It is shown that developing a globally robust model setup strongly depends on the choice of the the grazingn function. Especially its appropriateness for the applied phytoplankton formulation plays a crucial role.

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