Why does primary productivity vary with latitude?

Primary productivity varies with latitude primarily due to differences in sunlight availability, temperature, and nutrient availability. In tropical regions near the equator, there is abundant sunlight year-round, promoting high rates of photosynthesis. In contrast, higher latitudes experience seasonal variations in light and temperature, which can limit productivity during colder months. Additionally, nutrient availability can differ, with coastal areas often having higher productivity due to upwelling, while open ocean regions may be nutrient-poor, affecting overall productivity levels.