This study examines how chlorophyll-a (chl-a), an indicator of primary productivity, varies over the long term in the northern Bay of Bengal (BoB) and how it is influenced by major climate phenomena like ENSO and the Indian Ocean Dipole (IOD). Using satellite and reanalysis data from 1995 to 2024, the research finds that chl-a concentrations are highest near river mouths and increase during the summer monsoon. Overall, chl-a levels have been rising slightly each year, alongside warming sea surface temperatures and decreasing salinity. Nutrient availability, particularly nitrate and phosphate, strongly correlates with chl-a variability, while ocean currents also play a role. The analysis reveals that El Niño and positive IOD events tend to boost chl-a levels, whereas La Niña and negative IOD events often reduce them. These findings improve understanding of how climate variability and physical conditions control primary productivity in the BoB, supporting better fisheries management and blue economy initiatives.