Why are continental margins generally more biologically productive than the open ocean?

• A. They receive greater nutrient input from land runoff and upwelling, supporting higher primary productivity.
• B. They have higher salinity levels, which directly increase photosynthetic rates.
• C. They are less affected by sunlight, reducing competition among organisms.
• D. They experience lower rates of nutrient recycling, leading to nutrient accumulation.

Answer: (A)

Verified step by step guidance

1. Understand the concept of primary productivity: Primary productivity refers to the rate at which energy is converted by photosynthetic and chemosynthetic organisms into organic substances. It is influenced by the availability of nutrients, sunlight, and other environmental factors.
2. Analyze the role of nutrient input: Continental margins are closer to land, which means they receive significant nutrient input from land runoff. This runoff carries essential nutrients like nitrogen and phosphorus, which are critical for the growth of phytoplankton, the primary producers in aquatic ecosystems.
3. Consider the process of upwelling: Upwelling is a phenomenon where deep, nutrient-rich waters are brought to the surface. Continental margins often experience upwelling due to their proximity to coastal currents, further enhancing nutrient availability and supporting higher biological productivity.
4. Evaluate the role of salinity and sunlight: While salinity and sunlight are important factors for marine ecosystems, higher salinity levels do not directly increase photosynthetic rates, and continental margins are not less affected by sunlight. These factors are less relevant to the question of why continental margins are more biologically productive.
5. Clarify nutrient recycling: Nutrient recycling is a natural process in all ecosystems, including the open ocean. However, continental margins do not experience lower rates of nutrient recycling. Instead, the combination of land runoff and upwelling provides a continuous supply of fresh nutrients, supporting sustained primary productivity.