Sedimentation Deposition Patterns on the Chukchi Shelf Using Radionuclide Inventories

Sediment core collections and assays of the anthropogenic and natural radioisotopes, ¹³⁷Cs and ²¹⁰Pb, respectively, are providing long-term indications of sedimentation and current flow processes on the Chukchi and East Siberian sea continental shelf. This work, which has been integrated into interdisciplinary studies of the Chukchi Sea supported by both the US Bureau of Ocean Energy Management (COMIDA Hanna Shoal Project) and the National Oceanic and Atmospheric Administration (Russian-US Long Term Census of the Arctic, RUSALCA) includes studies of total radiocesium inventories, sedimentation rate determinations, where practical, and depths of maxima in radionuclide deposition. Shallow maxima in the activities of the anthropogenic radionuclide in sediment cores reflect areas with higher current flow (Barrow Canyon and Herald Canyon; 3-6 cm) or low sedimentation (Hanna Shoal; 1-3 cm). The first sedimentation studies from Long Strait are consistent with quiescent current conditions and steady recent sedimentation of clay particles. Elsewhere, higher and more deeply buried radionuclide inventories (> 2 mBq cm^-2 at 15-17 cm depth) in the sediments correspond to areas of high particle deposition north of Bering Strait where bioturbation in productive sediments is also clearly an important influence. Radiocesium activities from bomb fallout dating to ~1964 are now present at low levels (<1 mBq cm^-2) at the sediment surface, but burial of the bomb era radionuclide in sediments is observed to >20 cm. Independent sedimentation rate measurements with the natural radionuclide ²¹⁰Pb are largely consistent with the radiocesium measurements.