In the world ocean, flux of biogenic carbon and biogeochemical cycles of carbon and essential elements for primary production (Si, Fe, N) are influenced by complex biological processes and food-web interactions. Determination of key processes and their mechanistic understanding is required for an adequate parameterisation of these interactions in regional and global models that aim at predicting the response of ecosystems and biogeochemical cycles to global change. International research programs like IMBER call for a scientific approach that combines biological and biogeochemical expertise to achieve this goal. Further need for investigation exists especially for food web mediated recycling of elements and whether it takes place at the surface, in the mesopelagic zone or at the sediment.
The proposed study ZOOPALIS targets the effect of grazing on the dissolution of biogenic silica (BSi), Fe recycling and bioavailability, and decoupling of C, Fe, Si and N elemental cycles. Core to all experiments are diatom cultures, marked with multiple stable or radioactive isotopes. Special emphasis will be put on determining the speciation of recycled iron, in the light of Fe limitation of primary production in vast oceanic regions. Decoupling and recycling intensities will be assessed for key organisms (copepods, krill, appendicularians) and specialized feeding behaviour like benthic suspension feeding or coprophagic feeding of copepods.
Recycling and preservation of BSi embedded in fecal pellets will be studied by means o f batch and flow-through reactor experiments. Results will be integrated in 1D/3D coupled physical-biological models developed within the framework of ongoing studies making the proposed project strongly interdisciplinary in nature by combining, in a concerted effort, biological and biogeochemical expertise, as well as experimental and modelling work.
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