|Tidal Zone||Marine Oceanic Subtidal
|Definition||The Marine Oceanic Subsystem represents the open ocean, extending from the continental
shelf break to the deep ocean. Oceanic waters typically have salinity levels of =
36. Water depths typically range from 100 - 200 meters at their shallowest at the
shelf break to over 11,000 meters at the deepest point in the ocean.
The great depth of the Oceanic Subsystem is responsible for many of its characteristics. The oceanic water column tends to be more stable physicochemically; undergoing changes in temperature and salinity relatively slowly. Greater depth also diminishes the influence of the sea bottom on the overlying water column. Surface and bottom processes generally are poorly coupled and separated by great distances and thermocline layers. The waters of the Oceanic Subsystem receive little direct terrigenous input; the inputs from land typically occur indirectly, after passage through the substantial coastal water masses or atmospheric deposition.
Conditions in the Oceanic Subsystem are a function of the properties of the water column. For example, light penetration diminishes with depth (as sea water absorbs component wavelengths); thus, the quality and intensity of ambient light changes with depth. Little surface light penetrates below the photic zone (~200 meters). At greater depths, light is limited to that produced locally by bioluminescence. Water pressure also increases directly with depth because of the weight of the overlying water column, and water temperatures diminish with depth.