The influence of sedimentation regime on natural radionuclide activity concentration in marine sediments of the East Siberian Arctic Shelf

Abstract

Transport and accumulation of radionuclides in the Arctic depends on many biogeochemical processes, which are changing at accelerated rates due to climate change and human economic activity. We present the results of a study on the features distribution of some natural radionuclides in the marine sediments on the East Siberian Arctic Shelf collected during several expeditions from 2008 to 2019. Average activity concentration of ²³²Th, ⁴⁰K and ²²⁶Ra under the influence of different sedimentation regime increases from 40.7, 418 and 30.8 Bq/kg to 41.6, 423 and 34.9 Bq/kg respectively from coastal shelf marine sediments (<50% clay) to outer shelf marine sediments (>50% clay). Sediment particle size has a greater impact on radionuclides in the coastal shelf. An increase in the activity concentrations of ²³²Th and ²²⁶Ra with the increasing clay particles were found. On the outer shelf with a change in the sedimentation regime, the influence of the size composition decreased, at the same time, there is a correlation between the organic carbon concentration and the radionuclide activity concentration. Absolute maximums of natural radionuclide activity concentration (²³²Th = 70.9, ²²⁶Ra = 70.4, ⁴⁰K = 591 Bq/kg) were detected in the Chaun Bay. The highest activity concentration of ²²⁶Ra was found in paleo-river valleys marine sediments. A low ²³²Th/²²⁶Ra activity concentration ratio indicates the enrichment of paleo-river valleys marine sediments with ²²⁶Ra. In the deep-sea sediments of the shelf slope on the contrary paleo-river valleys, this ratio is greatly increased.

Keywords: East siberian arctic shelf; Marine sediments; Natural radionuclides; Organic carbon; Paleo-river valleys; Sedimentation regime.