Radiolarian responses of the central Okhotsk Sea to the global orbital and millennial scale climate oscillations over last 90 kyr

摘要

The study of total radiolarian content (TRC) and species richness (SR)for radiolarian assemblage as well as absolute and relative abundance of Cycladophora davisiana and abundance of other dominant taxa in the sediment core from the central Okhotsk Sea (OS) over last 90 kyr with previously established age model, position of millennial cycles of climatic changes and records of variations of various productivity proxies and activity of sea ices was carried out. The trends of TRC and SR in the radiolarian assemblage change synchronously on the orbital scale and are mainly determined by variations of paleoproductivity and input organic matter into the water column. In turn, the productivity of the OS depends, to a great extent, on conditions of the sea ice formation and distribution and increases during the warmer MIS 5a, 3 and 1 with a shorter seasonal sea ice cover. Among various productivity proxies considered by us, only Ba-bio reflects, to the fullest extent, the variations of TRC and SR of radiolarians, probably, due to the fact that the accumulation of insoluble barite in sediment depends on degree of organic matter decomposition immediately within the water column and provision of more favorable for radiolarian food.