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Quantifying the structure of the mesopelagic microbial loop from observed depth profiles of bacteria and protozoa
1Department of Biology, University of Bergen, Jahnebakken 5, PO Box 7800, N-5020 Bergen, Norway
2LOV-UMR7093, CNRS-UPMC, Station Zoologique, BP 28, F-06234 Villefranche-sur-Mer Cedex, France
Abstract. t is widely recognized that organic carbon exported to the ocean aphotic layer is significantly consumed by heterotrophic organisms such as bacteria and zooplankton in the mesopelagic layer. However, very little is known for the trophic link between bacteria and zooplankton or the structure of the microbial loop in this layer. In the northwestern Mediterranean, recent studies have shown that viruses, bacteria, heterotrophic nanoflagellates, and ciliates distribute down to 2000 m with group-specific depth-dependent decreases, and that bacterial production decreases with depth down to 1000 m. Here we show that such data can be analyzed using a simple steady-state food chain model to quantify the carbon flow from bacteria to zooplankton over the mesopelagic layer. The model indicates that a similar amount of bacterial production is allocated to viruses and heterotrophic nanoflagellates, and that heterotrophic nanoflagellates are the important remineralizers.
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Citation: Tanaka, T., Rassoulzadegan, F., and Thingstad, T. F.: Quantifying the structure of the mesopelagic microbial loop from observed depth profiles of bacteria and protozoa, Biogeosciences Discuss., 1, 413-428, 2004. Bibtex EndNote Reference Manager
