Impact of Natural and Anthropogenic Factors on Late Holocene Sedimentation in the Chukchi Sea

Late Holocene sediments have been recovered in a core from the central Chukchi Sea to reconstruct their accumulation conditions. The sediments consist mainly of terrigenous and just partly of biogenic material. Fine sand is dominated by up to 99.8% light fraction minerals, whereas heavy minerals account for not more than 1.4%. Results of magnetic susceptibility, related to the sand and heavy mineral content, decrease from the bottom to the top of the core. The species composition of pollen spectra varies insignificantly throughout the core and, on the whole, reflects the modern vegetation of the Chukchi Sea coast. The increased number of cysts of dinoflagellates and other aquatic palynomorphs, as well as some increased content of coarse-grained material at the upper part of the sediment core, is presumably caused by recent climate warming conditions. Two peaks of Cs-137 activity at the 7.5 and 1.5 cm in the core are related to radioactive fallout, caused by the accidents at the Chernobyl nuclear power plant in 1986 and the Fukushima nuclear power plant in 2011. The resulting sedimentation rates of 2.5-3 mm/yr correspond well to rates of sedimentation determined by 210Pb dating (2.0 mm/yr).