Correct option is a ( the amount of sunlight increases)
Explanation:
a. Sunlight does not penetrate the deep ocean it means at the bottom of ocean there is complete darkness. So when a submarine returns from the bottom of the ocean to the surface the amount of sunlight increases.
b.Usually temperature decreases with depth of ocean so this option is not correct.
c.This is also not correct option because on the surface of the ocean there may be island on which there may be lots of plants.
d. Pressure decreases on moving upward direction so this option is also not correct