Why do some water masses in subsurface oceans have little or no oxygen? a. Large carnivores deplete oxygen in subsurface oceans via their high rates of oxygen metabolism. b. Rates of photosynthesis are low in overlying waters, limiting the availability of oxygen. c. Waters underneath the surface oceans are cold and thus have a limited capacity to carry oxygen in solution. d. Rates of photosynthesis are high in overlying waters, supporting high rates of respiration in waters that deplete the oxygen there.