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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

The sublittoral macrofauna of the Steingrund, a stony area east-northeast of Helgoland, was investigated from May till October 1991 using a van Veen grab and a small dredge. The diverse endo-and epifauna of the sandy bottoms, pebbles and boulders of this Saalian end moraine comprised 289 taxa, whereby the polychaetes Magelona papillicornis, Lanice conchilega and Spiophanes bombyx dominated in terms of abundance. Species rare in the German Bight, such as the sponge Leucandra fistulosa, the sea urchin Echinus esculentus, and the sea anemone Haliplanella lineata, were also found. The two sample sets were processed separately with multivariate techniques, and differentiated on the basis of occurrence and numbers of the abundant species. The analysis of the grab samples revealed two types of the Tellina-fabula-community. These associations were differentiated by the presence of species of the coarse-sand-inhabiting Goniadefla-Spisulacommunity and were related to the distribution of the grain size of the sediment. Likewise, two epifaunal assemblages were distinguished. Sandy bottoms were characterized by Ophiura albida, l.uocarcinus holsatus and Pagurus bernhardus, while boulders and pebbles were covered by a varied sessile and mobile epifauna dominated by the sessile bryozoan Flustra foliacea and the mobile pantopode Aechelia echinata. Numerical density, biomass and annual production estimates are in the range of values determined for the macrobenthos of the German Bight, while annual P/B ratios mounted up to 5.

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