Planktonic foraminifera in the recent sediments of the Sea of Okhotsk

The distribution of planktonic foraminifera was studied in 25 samples of the surface sediments of the Sea of Okhotsk collected in cruise 53 of R/V Vityaz. Six species of planktonic foraminifera were identified in the bottom sediments. The species composition of this fauna is similar to that of the subarctic fauna from the Northwest Pacific Ocean. Neogloboquadrina pachyderma and Globigerina bulloides are the most widely spread and abundant species. Globigerina quinqueloba, Globigetinita glutinata, and Globigerinita uvula are spread in the regions of the influence of the Pacific Ocean currents entering the Sea of Okhotsk via the Kuril straits. The penetration of the relatively warm-water species Globorotalia scitula to the Sea of Okhotsk is related to the Tsushima and Soya currents. Only off southern Sakhalin were more warm-water (subtropical) species such as Globigerinoides ruber G. conglobatus, Globorotalia truncatulinoides, G. inflata, and G. hirsuta encountered The presence of these species in the southern part of the Sea of Okhotsk is also related to the warm Soya and Tsushima currents. The greatest abundance of planktonic foraminifer tests is noted in the central parts of the basin, where the plankton production is the highest, while the dilution by terrigenous, volcanogenic, and other biogenic matter is insignificant. The sediments of the near-shore regions are virtually free from planktonic foraminifera. The distribution of planktonic foraminifera in the recent sediments of the Sea of Okhotsk is closely related to the circulation pattern, temperature, and salinity of the surface waters and with their productivity. The formation of the communities strongly depends on the dissolution of the carbonate matter of the tests in the near-bottom waters undersaturated with carbonate and their dilution by terrigenous, volcanogenic, and biogenic (radiolarians and diatoms) matter.