Oceanographers divide the ocean into different vertical and horizontal zones based on physical and biological conditions. The pelagic zone consists of the water column of the open ocean , and can be divided into further regions categorized by light abundance and by depth. The photic zone includes the oceans from the surface to a depth of 200 m ; it is the region where photosynthesis can occur and is, therefore, the most biodiverse. Photosynthesis by plants and microscopic algae (free floating phytoplankton) allows them to create organic matter from chemical precursors including water and carbon dioxide. It is this upper sunlit ocean that creates the food supply that ultimately sustains most of the ocean ecosystem  . Light only penetrates to a  few hundred meters depth , so the remaining ocean below this is cold and dark. The continental shelf around the edge of the oceans is shallower (a few hundred meters or less) and this region is most impacted by human activity.
Oceanographers divide the ocean into different vertical and horizontal zones based on physical and biological conditions. The pelagic zone consists of the water column from surface to ocean floor throughout the open ocean . The water column is further categorized in other zones depending on light abundance and depth. The photic zone includes the water column from the surface to a depth of 200 m , where photosynthesis can occur . This makes the photic zone the most biodiverse. Photosynthesis by plants and microscopic algae (free floating phytoplankton) allows them to create organic matter from chemical precursors including water and carbon dioxide. This upper sunlit zone of the ocean ultimately sustains most of the ocean ecosystem since that is the origin of the food supply necessary to all life forms . Light only penetrates to a depth of a few hundred meters , so the remaining ocean below is cold and dark. The continental shelf where the ocean touches land is more shallow (a few hundred meters or less) and experiences more impact from human activity.
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