G. 1999 (March): Clay-mineral distribution in surface sediments of the Eurasian kctic Ocean and continental margin as indicator for source areas and transport pathwaysa synthesis. Boreas, Vol. 28, pp. 215-233. Oslo. ISSN 0300-9483. Clay-mineral distributions in the Arctic Ocean and the adjacent Eurasian shelf areas are discussed to identify source areas and transport pathways of terrigenous material in the Arctic Ocean. The main clay minerals in Eurasian Arctic Ocean sediments are illite and chlorite. Smectite and kaolinite occur in minor amounts in these sediments, but show strong variations in the shelf areas. These two minerals are therefore reliable in reconstructions of source areas of sediments from the Eurasian Arctic. The Kara Sea and the western part of the Laptev Sea are enriched in smectite, with highest values of up to 70% in the deltas of the Ob and Yenisey rivers. Illite is the dominant clay mineral in all the investigated sediments except for parts of the Kara Sea.The highest concentrations with more than 70% illite occur in the East Siberian Sea and around Svalbard. Chlorite represents the clay mineral with lowest concentration changes in the Eastern Arctic, ranging between 10 and 25%. The main source areas for kaolinite in the Eurasian Arctic are Mesozoic sedimentary rocks on Franz-Josef Land islands. Based on clay-mineral data, transport of the clay fraction via sea ice is of minor importance for the modern sedimentary budget in the Arctic basins.

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The surface water in the Transpolar Drift in the Arctic Ocean has a strong signature of 228 Ra. In an earlier study of 228 Ra in the open Arctic we showed that the major 228 Ra source had to be in the Siberian shelf seas, but only a single shelf station was published so far. Here we investigate the sources of this signal on the Siberian shelves by measurements of 228 Ra and 226 Ra in surface waters of the Kara and Laptev Sea, including the Ob, Yenisey and Lena estuaries.In the Ob and Lena rivers we found an indication for a very strong and unexpected removal of both isotopes in the early stage of estuarine mixing, presumably related to flocculation of organic-rich material. Whereas 226 Ra behaves conservatively on the shelf, the distribution of 228 Ra is governed by large inputs on the shelves, although sources are highly variable. In the Kara Sea the maximum activity was found in the Baydaratskaya Bay, where tidal resonance and low freshwater supply favour 228 Ra accumulation. The Laptev Sea is a stronger source for 228 Ra than the Kara Sea. Since a large part of Kara Sea water flows through the Laptev Sea, the 228 Ra signal in the Transpolar Drift can be described as originating on the Laptev shelf.The combined freshwater inputs from the Eurasian shelves thus produce a common radium signature with a 228 Ra/ 226 Ra activity ratio of 4.0 at 20% river water. The radium signals of the individual Siberian rivers and shelves cannot be separated, but their signal is significantly different from the signal produced on the Canadian shelf (Smith et al., in press). In this respect, the radium tracers add to the information given by Barium. Moreover, with the 5.8 year half-life of 228 Ra, they have the potential to serve as a tracer for the age of a water mass since its contact with the shelves. r