What provides the largest source of dissolved oxygen in the ocean?
a) coral reefs
b) tidal action
c) algal growth
d) hydrothermal vents

Most of the oxygen that exists in the ocean comes from phytoplankton that live near the surface of the ocean and are moved about by the ocean currents. Phytoplankton is a type of naturally occurring algae which would mean that the answer to this question is C "algal growth."

Ithink the answer you are looking for is (b).