Wanderlust World Wanderlust World Yes, a sea is smaller than an ocean.
| Feature | Ocean | Sea |
|---|---|---|
| Size | Vast, covering ~71% of Earth's surface | Smaller, subsidiary bodies |
| Boundaries | Defined by continents, ocean ridges, currents | Partially enclosed by land (marginal seas) or defined by currents (e.g., Sargasso Sea) |
| Depth | Average ~3,700 m; max 11,000 m (Mariana Trench) | Generally shallower; some deep (e.g., Caribbean ~7,700 m) |
| Number | 5 recognized (Pacific, Atlantic, Indian, Southern, Arctic) | Dozens (Mediterranean, Caribbean, South China, Bering, etc.) |
| Salinity | Relatively stable (~35 ppt) | More variable (Baltic ~8 ppt; Red Sea ~41 ppt) |
Seas are essentially subdivisions of oceans. For example, the Mediterranean Sea, Caribbean Sea, and Gulf of Mexico are all part of the Atlantic Ocean. The South China Sea and Philippine Sea are part of the Pacific Ocean.
Exception: The Sargasso Sea has no land boundaries—it's defined by ocean currents (North Atlantic Gyre).