DOC turnover in polar microbial food webs.

Microbial communities, including phytoplankton, protozoa, bacteria, archaea, fungi and virus, are by far the most abundant and the most taxonomic and genetically diverse group of organisms in marine pelagic ecosystems. Biological activity, biomass, produc tion and remineralization in these systems are essentially microbial while higher trophic levels play a minor role in quantitative terms. Microorganisms are the main drivers of biogeochemical cycles and the major producers and consumers of green-house gas es, and they are therefore significant players in regulating the ecosphere. The main hypothesis of PAME-Nor is that heterotrophic bacteria in the photic zone of polar pelagic ecosystems may be in two different states, carbon- or mineral nutrient limited , and that the state realized directs the composition of the microbial community and the flux of carbon and other elements through the food web. Our field experiments and campaigns will investigate the POC-DOC flux and the ability of the polar microbial ecosystems to consume organic material. By focussing on the role of the microbial food web in the ocean?s C-cycle, our study will have direct implications for atmospheric uptake of CO2 and thus the role of Polar oceans in climate change. Another highly re levant aspect of our research is that bioremediation and bacterial consumption of oil spills in Arctic waters may be anticipated to depend strongly on which of the two states the pelagic ecosystem reside in.