Sedimentation Rates in Different Facies–Genetic Types of Bottom Sediments in the Kara Sea: Evidence from the 210Pb and 137Cs Radionuclides

Resumo

The paper presents authors' original data on the isotope composition of the natural “excess” Pb‑210 and artificial Cs-137 radionuclides in the upper 25- to 50-cm layer of sea-bottom sediments in the Kara Sea (from the Ob and Yenisei estuaries, Eastern Novaya Zemlya trough, Voronin trough, and Sedov bay at the Novaya Zemlya). Sediment cores were collected during Cruises AMK-63 and AMK-66 of the R/V Akademik Mstislav Keldysh in 2015 and 2016. Results of this research show strong correlations between the sedimentation rates and facies-genetic types of the sea-bottom sediments. The highest sedimentation rates are typical of the terrigenous–estuarine sediments, which are subdivided into tractional load, whose sedimentation rate is 0.4–0.7 cm per year, and “mud bank” sediments, whose sedimentation rate is 0.7–1.0 cm per year. The terrigenous shallow marine sediments are characterized by the lowest sedimentation rate of 0.1–0.3 cm per year. The background terrigenous marine sediments show broad variations in the sedimentation rates: these rates are at a minimum (and comparable to the sedimentation rates of the terrigenous shallow marine sediments) on trough slopes and can increase to 0.9 cm per year in the central parts of the trough (as a result of gravity creep). The glacial sediments of Novaya Zemlya bays belong to a separate individual type. The measured “current” sedimentation rate within the inner depression of the Sedov bay is 0.1–0.2 cm per year.