Answer to Question 1
D
Answer to Question 2
The overall effect of photosynthesis in shallow waters, of the settling of organic matter, and of decomposition in deep waters is the transfer of CO2 and nutrients from the surface waters to the deep ocean. This process is known as the biological pump. It is balanced by upwelling (see Chapter 5), which brings nutrients and carbon-rich waters back to the surface, replenishing the nutrients and carbon removed by the biological pump. The biological pump has a profound effect on ocean chemistry. As a result of its operation, surface waters are measurably depleted in carbon and severely depleted in phosphate and nitrate (the major nutrient elements) relative to deep waters. If the biological pump were to ceasefor example, as the result of a mass extinctionthe ocean would assume a more uniform composition in a few thousand years, as the thermohaline circulation homogenized the ocean.
