Final answer:
Primary productivity in polar oceans is limited by low sunlight availability during extended polar winters and a shortage of crucial nutrients, specifically nitrogen in the Atlantic and iron in the Pacific, which are essential for phytoplankton growth.
Step-by-step explanation:
Primary productivity in polar oceans is largely limited by the availability of sunlight and essential nutrients such as nitrogen and iron. Sunlight is a crucial factor as it drives the photosynthetic process in phytoplankton, the primary producers in the ocean. During polar winters, the sun is below the horizon for extended periods, significantly reducing the availability of sunlight. Additionally, although polar waters can be rich in nutrients due to upwelling and other oceanic processes, the availability of specific nutrients like nitrogen in the Atlantic Ocean and iron in the Pacific Ocean limits phytoplankton growth. In polar oceans, these conditions contribute to lower net primary productivity compared to more temperate or tropical regions.