Hydrological Changes in the Laptev Sea during the Holocene Inferred from the Studies of Aquatic Palynomorphs

摘要

Based on the study of aquatic palynomorph assemblages in two Holocene sediment cores obtained from the eastern Laptev Sea shelf,the main stages in the postglacial transgression are reconstructed for the last 11.3 ky.During that period,the inner shelf of the Laptev Sea(sea depth of 51 m)was already flooded representing an area of intense freshwater sedimentation in the immediate proximity from the river mouth in the period of 11.3 to 10.3 ky B.P.Approximately 1.0-1.5 ky later,the inner shelf(sea depth of 32 m)was flooded,although it remained under the influence of the river runoff up to 7.4 ky B.P.The period of 10.3-7.4 ky B.P.was marked by the dominant dinoflagellate cysts Operculodinium centrocarpum among the aquatic palynomorphs,the appearance of more thermophilic dinoflagellate species,and elevated values of the AH ratio,which indicates an enhanced influx of relatively warm North Atlantic waters to the Laptev Sea shelf.The environment close to the present-day one became dominant on the outer and inner shelf of the Laptev Sea approximately 8.6 and 7.4 ky B.P.,respectively.