<u><em>As It's Typically Defined As The Area Of The Ocean Lying Beyond The Continental Shelf</em></u>
Operationally It's often referred to as beginning where the water depths drop to below 200 meters (656 feet), seaward from the coast to the open ocean.
gas exchange is a primary example of simple diffusion,the exchange of *oxygen* and *carbon dioxide* fuels the cellular processes such as photosynthesis and cellular respiration