When we think of vast bodies of water, our minds often drift to images of endless blue horizons, waves crashing against sandy shores, and the serene quiteness of aquatic life. But what exactly differentiates a sea from an ocean?
While size is probably the most distinguishing feature, in that oceans are much larger than seas, there are several other differences that define these two kinds of water bodies. From their different ecosystems and geography to their varying depths and salinity levels, understanding these factors can make the picture clearer.
Based on geographical locations
One of the main differences between seas and oceans is their geographical location. Oceans are large, continuous bodies of saltwater that cover approximately 71% of the Earth’s surface, connected to the global oceanic system. There are five major oceans on our planet: the Pacific, Atlantic, Indian, Southern, and Arctic. Each ocean is connected, allowing for the continuous flow of water and marine life across the globe.
Seas are a smaller body of saltwater, usually mostly enclosed by land. They generally lie along the boundaries of oceans, with narrow passage or straits connecting them. Some of the notable seas are the Mediterranean Sea, the Caribbean Sea, and the South China Sea. Therefore, seas have a geographical disposition that makes it easier for man to carry out fishing, shipping, and tourism among other activities.
On the basis of depth and volume
Another major difference between seas and oceans is their depth and volume. Oceans are much deeper and hold a greater volume of water than seas. The average depth of the world’s oceans is about 12,080 feet (3,682 meters), with the deepest point, the Challenger Deep in the Mariana Trench, reaching approximately 36,070 feet (10,994 meters). Oceans present wide, open spaces that stretch to the abyssal plains, the trenches, and the mid-ocean ridges.
Seas are comparatively shallower, with average depths ranging from several hundred to thousands of feet. For example, the Mediterranean Sea has an average depth of about 4,900 feet (1,500 meters). The nature of seas to be shallower allows for higher penetration of light; this can host a different marine life compared to those in the oceanic environments of deeper and darker waters.
Depends on salinity levels also
Salinity may also vary among seas and oceans. Even though they are salty water, salinity is more prominent in seas compared to the oceans due to the nearness to the shore and effects of river inflow, evaporation, and low exchange with the open ocean. The Dead Sea is a classic example with a highly high salinity content and, hence, considered to be one of the saltiest water bodies in the world. This high salinity is as a result of the high rates of evaporation and minimal influx through rivers.
Generally, the size of the ocean and the continuous movement of water render its salinity relatively stable and at lower values. The mean salinity of sea water is around 35 ppt. In comparison, seas vary widely with regard to salinity depending on location and environment
Climate influence also plays an important role
Oceans play an important role in Earth’s climatic regulation due to their massive area, whereby they absorb the heat from the sun and release it at certain times. As such, the tremendous area of ocean covers large capacities to store immense amounts of solar energy. Ocean currents are then supposed to transport them around the entire globe.
Seas, though still having an important influence on the local climates, are relatively less powerful than oceans. Thus, the smaller size and shallower depth of seas allow fewer heat storages and mean them to have less influence on global climate patterns. Nevertheless, seas do play an important role in regional climates, especially in coastal areas, where they moderate temperature and encourage unique weather conditions.
