Use the Following Figure to Answer the Question

Multiple Choice

Use the following figure to answer the question. Which of the following conclusions about productivity within the confines of the experimental ecosystem is most consistent with the data?

A) Productivity is higher at depth than at the surface, but only initially.
B) Productivity is higher at the surface than at depth; however, an additional experiment could further test the effect of depth by introducing FeSO4 at 30 m deep and measuring the chlorophyll a response.
C) Productivity is higher at the surface than at depth, and would be predicted to increase sharply after day 12.
D) Productivity at a depth of 30 m is low only because of a lack of sunlight, not a lack of iron sulfate.