Foraminifera in surface sediments of the Bering and Chukchi Seas and their sedimentary environment

Based on a quantitative analysis of foraminifera in 39 surface samples of the Bering and Chukchi Seas,the nearly absence of planktonic foraminifera in the surface sediments can be related to the low surface primary productivity and strong carbonate dissolution in the study area.It has been revealed that the surface primary productivity,and carbonate dissolution and properties of water masses related to the water depth mainly control the distribution of benthic foraminifera.The shelf of the Chukchi Sea is dominated by the Elphidium spp.assemblage and Nonionella robusta assemblage with low foraminiferal abundance and diversity,which is controlled by the coastal water mass of the Arctic Ocean.The slope of the Bering Sea is dominated by the Uvigerina peregrina-Globobulimina affinis assemblage with abundant N.robusta,and relatively high foraminiferal abundance and diversity,which is controlled by the intermediate and deep water masses of the Pacific Ocean.However,the Bering Sea has relatively shallow carbonate lysocline and compensation depth (CCD),at about 2 000 and 3 800 m,respectively.In addition,there exists Stetsonia arctica in the surface sediments of the upper slope in the Bering Sea,which is a typical deep-sea benthic foraminiferal species of the slope in the Arctic Ocean.This indicates that the deep water of the two seas beside the Bering Strait had ever exchanged.