Question

In the dark waters just below the photic zone, because of cellular respiration, the concentration of dissolved __________ is higher relative to dissolved __________. carbon dioxide. . . . oxygen oxygen. . . . carbon dioxide

Answer 1

In the dark waters just below the photic zone, because of cellular respiration, the concentration of dissolved carbon dioxide is higher relative to dissolved oxygen. 
In cellular respiration living organisms use oxygen and release carbon dioxide, because there is little or no light there is no photosynthesis and oxygen is little produced.