Difference between Sea and Ocean, Area, Depth, Salinity

Area

Seas are much smaller in size. Example: The Arabian Sea covers an area of ~3.862 million km²,

The Oceans are vast saltwater bodies covering ~71% of the earth and hold ~97.5% of total water. Eg: Pacific Ocean covers ~30% of the earth (largest).

Number

There are about 50-60 Seas in the world. Eg: Red Sea, Mediterranean Sea, Black Sea, Dead Sea, Arabian Sea, etc.

There are 5 Oceans in the world including- Pacific, Arctic, Atlantic, Indian and

Southern Ocean.

Depth

The seas are generally shallower and not as deep as Oceans. Many of them lie on the continents shelves, far from the oceans.

The oceans are deep and extend up to 11000 km beneath. The Challenger Deep is the deepest point located in the Mariana Trench of the Pacific Ocean.

Location

They are located near the continental regions, often enclosed within the landmass. Eg: Caspian Sea is landlocked entirely while Red Sea is partially enclosed.

They are located between the continents on the Earth and form a continuous saltwater body.

Water Volume

The volume of the water in the sea is much lower than that of the oceans. They hold only a small fraction of oceanic water due to less space. 

The volume of Oceanic Water is approximately 1.35 billion cubic kilometers, accounting for about 97.5% of all the water on Earth

Salinity

The salinity of the seas often fluctuates. Evaporation leads to higher concentration of salts while inflow of river decreases the level of salinity. Eg: Dead Sea has 33.7% salinity (highest).

Salinity in oceaning water is usually uniform due to the transport of water from equator to the poles through oceanic currents. The average salinity is ~35 ppt (3.5%).

Water Current and Circulation

Seas have more restricted water movement; currents and mixing depend on connection with ocean and coastline shape.

Oceans feature large-scale global currents (thermohaline circulation) that distribute heat and regulate global climate.

Climate Influence

It has influence on the regional or local weather phenomenon including: coastal weather, humidity, storms near coastlines.

Oceans play a major role in regulating Earth’s climate by absorbing solar heat and distributing it globally.

Biodiversity & Ecosystem

They often support rich and diverse ecosystems. Eg: coral reefs, coastal fish, seaweed, because of shallow depths and sunlight.

They support a wide range of marine life including deep‑sea species adapted to high pressure, low light, vast zones, often independent of sunlight. Eg: Yeti Crabs, Gulper Eels, Anglerfish, etc.

Human Activities

These are near to the coasts thus are more accessible for fishing, ports, local trade, and human settlement along coastlines.

They are used for global shipping routes, long‑distance travel, and connect continents across vast distances.

Relation with Continents

Seas usually lie at the edges of continents or between islands and continents; they are coastal or marginal waters.

Oceans lie between continents, connecting them via water routes, and are not bound by continental edges.

Water Exchange/ Mixing

Seas may have limited exchange if partially enclosed, water movement may be restricted, leading to altered salinity, temperature or ecology.

Oceans have continuous mixing, exchange over vast connectivity and are part of a single global oceanic system.

Effects of Sunlight

Due to shallower depths, sunlight tends to penetrate more which allows photosynthesis, supporting coral reefs and abundant plants/ algae.

In oceans, deep zones often get little/ no sunlight. Therefore many deep‑sea species do not depend on photosynthesis (eg: Bacteria, Planktons, etc.).