Coccolithophores, fundamental primary producers in the ocean, have a vital function in the carbon cycle through photosynthesis and synthesizing calcium carbonate plates (coccoliths). Since the last glacial period, the coccolith assemblages in the eastern Indian Ocean have experienced significant changes, which coincide with climatic and oceanographic variations. Our study is based on quantitative analysis of coccolith assemblages in a sediment core of YDY05, recovered from the north-eastern part (Bay of Bengal) of the Indian Ocean (9.99°N, 90.32°E, water depth 3310m). This study investigates Milankovitch cycles in coccolith assemblages and calculate primary productivity. By analyzing sediment cores, we can detect distinct cyclic patterns in coccolith primary productivity, which are associated with variations in monsoonal strength and ocean circulation influenced by these astronomical cycles. The results of our study reveal that average percentage of Florisphaera profunda is approximately 56.71% while 10.72% Emiliania huxleyi and 25.04% Gephyrocapsa oceanica of the total countable number. The productivity gradually increased during the period between 8 and 16 kyr. The high abundance of F. profunda suggests that variations in nutrient availability, caused by changes in water column stratification and monsoonal intensity, were strongly linked to periods of precession and semi-precession. E. huxleyi and G. oceanica show distinct variations in their abundance and response to changes in nutrient availability, influencing regional primary productivity. E. huxleyi thrives in cooler, nutrient-poor waters, while G. oceanica is more dominant in nutrient-rich, warmer conditions, both playing key roles in carbon cycling and biological productivity. Our findings indicate that the precession and semi-precession components of the Milankovitch cycle were crucial in regulating the availability of nutrients and the stratification of the water column.

coccolithophores, Milankovitch cycles, primary productivity, nutrient availability, monsoonal strength