Distribution and influencing factors of planktonic foraminifera in surface sediments of the Ninetyeast Ridge in Indian Ocean

Eighty-two surface sediment samples were collected from the Ninetyeast Ridge of the eastern Indian Ocean, from which planktonic foraminifera community fossils were identified and statistically analyzed. The regional distribution characteristics of planktonic foraminifera in surface sediments were revealed, and the influencing factors discussed. Results show that the planktonic foraminifera displayed typical tropical-subtropical attributes, and 30 species of planktonic foraminifera were identified. The planktonic foraminifera were classified into groups (assemblages) in cluster analysis. Group I included mainly Globigerinoides sacculifer, Globigerinoides ruber, and Neogloboquadrina dutertrei, distributed mostly in the open sea area in the south of the Bay of Bengal from 5°N to 10°N, and affected by productivity and salinity of seawater. Group II included Globigerinoides ruber, Globorotalia menardii, and Neogloboquadrina dutertrei, occupied mainly between 5°N and 5°S along the Ninetyeast Ridge, and related to the depth and productivity. Group III contained mainly Globorotalia tumida, Globorotalia menardi, and Pulleniatina obliquiloculata, distributed symmetrically in deep water areas on both sides of Group 2, and were closely depth dependent. Therefore, the distribution patterns of planktonic foraminifer assemblages are closely affected by water depth, salinity, and productivity of planktonic foraminifera in the sea area.