| Summary: | Human-induced CO2 emissions to the atmosphere cause climate change and ocean acidification. The strongest indicators of climate change and ocean acidification are expected to be found in the Arctic Ocean (AO). The AO area is small compared to the world ocean, but the global influence of its carbon biogeochemical system with large spatial and temporal variability is considerable and complex. The AO carbon biogeochemical system is also expected to experience feedback in regard to climate change, and to influence the energy flow throughout the Arctic food web. This thesis investigates the carbon biogeochemical system in the AO: present variability; coupling with processes at the low trophic level; and response to future climate and CO2 scenarios. The study combines differing methodological approaches: (i) in-situ observations, (ii) field perturbation experiments, and (iii) ecosystem modeling. The thesis is based on four separate papers. Paper I describes the natural variability of particulate organic carbon and particulate organic nitrogen in a composition of seston and estimates the carbon to nitrogen (C:N) ratio in the AO seston. The paper is based on 3672 in-situ measurements gathered from sources both published and unpublished. The overall C:N ratio in seston was 7.4, which is significantly higher than the classical Redfield ratio of 6.6. A great regional variability in the seston C:N ratio was found. Paper II introduces the inorganic carbonate system around the Svalbard archipelago in the AO, at present and under future climate and CO2 scenarios. This paper is based on results from a coupled physical-biogeochemical ecosystem model forced by SRES A1B scenario, as well as on results of a CO2 perturbation study on the natural community conducted in an Arctic fjord. The results presented in this paper suggest that seawater pCO2 in the area around Svalbard at the end of the 21st century will be 300 μatm higher than at present in the Atlantic influenced region, and 400 μatm higher than at present in the Arctic ...
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