How does the concentration of prokaryotic cells at the surface of pelagic water compare with the concentrations at depths below 1000 m?

A) There is a decrease in concentration from 1 m to 1000 m in depth, then a dramatic increase below 1000 m.
B) There is a decrease in concentration with increasing depth.
C) There is a steady increase in concentration with increasing depth.
D) There is an increase in concentration at depths below 1000 m.