Global climate change has a particularly strong influence on the arctic zones. The warming of permafrost increases both methane emissions and the mobilization of organic material (Tarnocai et al. 2009). Both processes may cause, by the production of climate-relevant gases CH4 and CO2, a positive feedback with the climate and could further aggravate the current situation. In permafrost soils of the tundra and taiga the stored soil organic carbon is estimated to be up to 60% of the world carbon resources (Dixon et al. 1994, Tarnocai et al. 2009) and the boreal river systems which drain the Arctic have the world’s highest DOC concentrations (Dittmar et al. In 2003, Raymond et al. 2007). The first signs of a large-scale response to the recent warming of the last decades have already been observed (Peterson et al. 2002). Under conditions of progressive warming, an increase of the runoff and thus the mobilization and transport of the Arctic permafrost and artic vegetation zones stored carbon reserves are expected (Freeman et al. 2001). Together with the increasing flow of loads of silicate, phosphate and trace elements a change in the production/degradation equilibria and the carbon cycle of the receiving marginal seas can be expected. Is a crucial and much-debated question if to what extent and at what time scales the registered terrigenous DOC (Tdoc) can be microbially degraded in the sea and what factors control this process (Hansell et al. 2004). Generally it is assumed that the mainly of humic substances consisting Tdoc is largely refractory and resistent to microbial degradation (Dittmar et al. 2003). On the other hand, the low concentrations of Tdoc in the open ocean (Opsahl and Brenner 1997). Overall, the underlying processes of microbial degradation and chemical modification are poorly understood. Factors such as photo-oxidation, limitation by inorganic nutrients and salinity are likely to have a significant influence on the degradability of Tdoc in the sea (Lignell et al. 2008). Almost no studies exsist on the identification and interaction of the microorganisms involved with the various components Tdoc and the influence of abiotic factors on microbial degradation.

 

Photos by I. Krämer and D. Herlemann

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