|Definition||The Marine System is defined by salinity, which is typically about 35, although salinity
can measure as low as 0.5 during the period of average annual low flow near fresh
outflows. This system has little or no significant dilution from fresh water except
near the mouths of estuaries and rivers. The Marine System includes all non-estuarine
waters from the coastline to the central oceans. The landward boundary of this system
is either the linear boundary across the mouth of an estuary or the limit of the supratidal
splash zone affected by breaking waves. Seaward, the Marine System includes all ocean
The Marine System is typified by waves, currents and coastal water regimes determined by oceanic tides. Coastal indentations and bays that do not receive appreciable and regular freshwater inflow are part of the Marine System. Areas where river plumes discharge directly into marine waters without geomorphological enclosure are also part of the Marine System. In such areas, (e.g., Mississippi River plume, Chesapeake Bay plume), low salinity water and fresh plumes may discharge from the seaward boundary of the estuary, extending far into the Marine System beyond the enclosed part of the estuary. These freshwater features are considered to be Hydroforms within the Marine System (see Section 5).
The Marine System has three subsystems (which are defined by depth): Nearshore, Offshore, and Oceanic.