Siberia occupies a significant part of the Eurasian continent and environmental changes in this region can have an important impact on the climate system of the Northern Hemisphere. The sediment flux of Siberian rivers is sensitive to changes in physical, chemical, and biological processes taking place on the continent, and these changes can be recorded in marine sediments on the Siberian Arctic Shelf. This paper presents data on grain-size distribution of the sediments, the sedimentation rates, and the mass accumulation rates on the shelf over the past 100 years. Age models are based on the decay rate of excess lead isotope 210Pb, taking into account the sorption capacity of the marine sediments, and the presence of cesium isotope 137Cs peaks in the sediment cores. The highest sedimentation and mass accumulation rates were observed prior to the 1920–40 and coincide with larger particle sizes, indicate a period of active sediment-laden sea ice and iceberg melt. Systematic decrease in the sedimentation and mass accumulation rates against the background of an increase in the proportion of silt fractions in the shelf sediments in the second half of the 20th century can be explained by an acceleration of the arctic hydrological cycle.

The distribution of 137Cs and 239,240Pu in various ecosystems of the Kara Sea as well as speciation of these radionuclides has been studied to assess their potential mobility. In bottom sediment and seawater samples collected in Abrosimov, Tsivolky, Stepovoy, and Sedov Bays and on the coast of Novaya Zemlya, the content of anthropogenic radionuclides 137Cs and 239,240Pu does not exceed the values typical of the offshore zone in the Kara Sea (in sea water: 1.0–3.7 Bq/m3 for 137Cs and 50–90 mBq/m3 for 239,240Pu; in bottom sediments: 0.5–18.3 Bq/kg for 137Cs and 4.3–7.3 Bq/kg for 239,240Pu). The present monitoring study is important for the development of a long-term forecast for the dynamics of environmental contamination in the shallow bays of Novaya Zemlya.