HOLOCENE OF THE EURASIAN ARCTIC SEAS (DIA TOM BIOSTRATIGRAPHY AND PALEOCEANOGRAPHY)

Piston core in the Eurasian Arctic shallow seas show consistent change s in relative abundance of diatom valves, ecological and biogeographic al composition of diatom assemblages throughout the Holocene. Five eco logical diatom zones established in the arctic shelf sediments are cha racterized by strustural changes in diatom assemblages reflecting the main stages of paleoceanological development of the Arctic seas during the Holocene. Diatom assemblages of the Ecozones V and IV display con sequent sea-level rise during the Holocene transgrassion accompanied b y formation of the modem hydrobiological and sedimentological conditio ns in the Arctic seas. Ecozone III is the marking one for the Holocene sediments of the Arctic shelf. Its diatom assemblages reflect the mos t favorable hydrobiological conditioons for the arctic phytocenoses de velopment (''hydrobiological optimum''). Age estimations for the Ecozo ne III are the following: for the Chukchi Sea 6.5-2.7 Ka, for the East Siberian Sea 5-2.5 Ka, for the Parents Sea 5.7-3.7 Ka. Short-lasting period coinciding with the Ecozone II is characterized by production f all, elimination of the most warm-water species and increase of the cr yophillic sea-ice species abundance in several regions. Environmental conditions of the Arctic seas since 1.5-1.1 Ka (Ecozone I) resembled t he present ones.