Terrestrial organic carbon dynamics in Arctic coastal areas budgets and multiple stable isotope approaches

Arctic rivers transport 31-42 Tg organic carbon (OC) each year to the Arctic Ocean, which is equal to 10% of the global riverine OC discharge. Since the Arctic Ocean only holds approximately 1% of the global ocean volume, the influence of terrestrially derived organic carbon (OC ter ) in the Arctic Ocean is relatively high. Despite the global importance of this region the behavior of the, by far largest fraction of the OC ter , the dissolved organic carbon (DOC) in Arctic and sub-arctic estuaries is still a matter of debate. This thesis describes data originating from field cruises in Arctic and sub-arctic estuaries and coastal areas with the aim to improve the understanding of the fate of OC ter in these areas, with specific focus on DOC. All presented studies indicate that DOC ter and terrestrially derived particulate organic carbon (POC ter ) are subjected to substantial degradation in high-latitude estuaries, as shown by the non-conservative behavior of DOC in the East Siberian Arctic Shelf Seas (ESAS) (paper I) and the even more rapid degradation of POC in the same region (paper II). The removals of OC ter in Arctic shelf seas were further supported by multiple isotope studies (paper III and IV), which showed that a use of 13 C/ 12 C in both OC and DIC, together with 34 S/ 32 S is a powerful tool to describe the sources and fate of OC ter in estuaries and coastal seas. High-latitude estuaries play a key role in the coupling between terrestrial and marine carbon pools. In contrast to the general perception, this thesis shows that they are not only transportation areas for DOC ter from rivers to the ocean, but are also active sites for transformation, degradation and sedimentation of DOC ter , as well as for POC ter . In a rapidly changing climate, the importance of these areas for the coupling between inorganic and organic carbon pools cannot be underestimated. At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 2: Submitted. Paper 4: Manuscript. Härtill 4 uppsatser Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010 filosofie doktorsexamen Doctor philosophiae Degree of Doctor of Philosophy doctorat ès lettres Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm Härtill 4 uppsatser Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010 filosofie doktorsexamen Doctor philosophiae doctorat ès lettres Arctic rivers transport 31-42 Tg org