Marginal Seas
Geography › Ocean Relief, Oceans and Seas · Topic 10.6
A marginal sea is a part of an ocean that is partly enclosed by land, islands or island arcs and lies on the continental shelf, such as the East China Sea or the Arabian Sea. Mediterranean seas, such as the Mediterranean and the Caribbean, are almost enclosed by land, and inland seas such as the Caspian have no outlet. Their salinity, tides and uses differ from the open ocean.
6 min read · UPSC Prelims · Geography · Ocean Relief, Oceans and Seas
At a Glance
- Marginal sea Partly enclosed part of an ocean
- Mediterranean type Almost enclosed, joined by a narrow strait
- Inland sea No outlet: Caspian, Aral
- Largest sea by area Philippine Sea
- Lowest land point Dead Sea shore
- Exam link UPSC Prelims, Geography: Ocean Relief, Oceans and Seas
Where Does It Fit?
This is the sixth topic of the category on ocean relief, oceans and seas. The previous topic described the Indian Ocean, and this one covers the seas that fringe the oceans. The last topic of the macro covers bays, gulfs, straits and isthmuses. Previous topic: The Indian Ocean. Next topic: Bays, Gulfs, Straits and Isthmuses.
What Are Marginal Seas and How Are They Classified?
In short: a sea is a smaller part of an ocean that is partly shut in by land.
The oceans have a fringe of smaller water bodies called seas. They lie on the continental shelf, are shallower than the open ocean, are strongly affected by the land, and are often rich in fish and oil. They are classified by how enclosed they are.
- Marginal seas: open to an ocean over a wide connection, but partly bounded by islands or peninsulas, such as the Arabian Sea, South China Sea, East China Sea, North Sea and Bering Sea.
- Mediterranean seas: almost enclosed by land and joined to the ocean by a narrow strait, such as the Mediterranean Sea, the Black Sea, the Red Sea, the Caribbean and the Baltic Sea. Because of the narrow connection, their water properties differ strongly from the ocean.
- Inland or enclosed seas: completely landlocked, with no connection to the ocean, such as the Caspian Sea, the Aral Sea and the Dead Sea. They are strictly large lakes, but are named seas.
The Philippine Sea is the largest by area, followed by the Coral Sea and the Arabian Sea. A sea is different from a bay or gulf, which is a coastal indentation, as in Bays, Gulfs, Straits and Isthmuses.
Which Are the Important Seas of the World?
| Sea | Location and connection | Special features |
|---|---|---|
| Mediterranean Sea | Between Europe, Africa and Asia; joined to the Atlantic by the Strait of Gibraltar, to the Red Sea by the Suez Canal and to the Black Sea by the Dardanelles and Bosphorus | High evaporation makes it more saline than the Atlantic, about 38 parts per thousand; almost tideless; cradle of ancient civilisations; Mediterranean climate |
| Black Sea | Between Europe and Asia; joined to the Mediterranean by the Bosphorus | Low salinity because of large river inflow; deep water has no oxygen and holds hydrogen sulphide; major ports and grain export route |
| Red Sea | Between Africa and Arabia; joined to the Arabian Sea by Bab-el-Mandeb and the Gulf of Aden | A young sea in a rift valley where the African and Arabian plates are moving apart; very warm and salty; coral reefs; the Suez Canal route |
| Caspian Sea | Between Europe and Asia; landlocked | The largest enclosed inland water body in the world; slightly saline, much lower than the ocean; rich in oil and gas; sturgeon and caviar |
| Dead Sea | Between Israel, Jordan and the West Bank; landlocked | Shore is the lowest land area on Earth, over 400 m below sea level; extremely salty so that swimmers float; shrinking as the water level falls by around a metre a year |
| Aral Sea | Kazakhstan and Uzbekistan | Dried up since the 1960s after the Amu Darya and Syr Darya were diverted for cotton irrigation; one of the greatest environmental disasters |
| South China Sea | Between mainland Asia, the Philippines, Borneo and Taiwan; joined by the Malacca and Taiwan straits | Vital trade route and fishing area with oil and gas; disputed islands, and the 2016 arbitral tribunal ruling under UNCLOS, which China does not accept |
| North Sea | Between Britain and mainland Europe | Shallow shelf; big oil and gas fields; Dogger Bank fishing; busy shipping |
| Baltic Sea | Surrounded by Scandinavia and northern Europe; joined to the North Sea by narrow Danish straits | Brackish, with low salinity of about 7 parts per thousand, because of river inflow and low evaporation; freezes in winter |
| Caribbean Sea | Between the West Indies and Central and South America | Warm, hurricane breeding ground; coral reefs; the Panama Canal on its western edge |
What Are the Other Seas to Know, Including India’s?
- Arabian Sea: the part of the Indian Ocean between India and Arabia, with the ports of Mumbai, Kandla and Karachi, and the Bombay High oil field, as in The Indian Ocean.
- Andaman Sea: east of the Andaman and Nicobar Islands, linked with the Strait of Malacca.
- Laccadive Sea: the sea off the southwestern coast of India, around Lakshadweep and the Maldives.
- Sea of Japan, Yellow Sea, East China Sea and Sea of Okhotsk: the marginal seas of East Asia with rich fisheries; the Yellow Sea is named for the silt of the Yellow River.
- Bering Sea: between Siberia and Alaska, linked to the Arctic by the Bering Strait.
- Sargasso Sea: a sea with no land boundary, defined by the currents of the North Atlantic gyre, as in The Atlantic Ocean.
As an analytical point, seas show how geography, climate and politics interact: the Mediterranean’s salinity is the result of evaporation, the Baltic’s of the river inflow, the Aral’s of human diversion of rivers, and the South China Sea’s of a dispute over islands whose meaning arises from the Law of the Sea, as in UNCLOS, Territorial Waters and Exclusive Economic Zone.
Why Is This Topic Important?
- Map-based Locations asked every year
- Environment Aral and Dead Sea
- Geopolitics South China Sea
What Came Next?
The last topic of the macro describes bays, gulfs, straits and isthmuses. Next topic: Bays, Gulfs, Straits and Isthmuses.
Key People and Terms
- Marginal sea Partly enclosed ocean fringe
- Mediterranean sea Almost enclosed sea with a narrow outlet
- Inland sea Landlocked salt water body
- Brackish Water of low salinity
- Bosphorus Strait linking the Black Sea and Marmara
- Arbitral tribunal Body that decides a legal dispute
Exam Corner
Points to Remember
- The Caspian is the largest enclosed inland water body.
- The Dead Sea shore is the lowest land.
- The Red Sea lies in a rift.
- The Baltic Sea is brackish.
- The Aral Sea dried up after river diversion.
Do Not Confuse With
- Sea and lake Salt water, often connected versus freshwater, landlocked
- Bosphorus and Dardanelles Black Sea outlet versus Marmara-Aegean outlet
- Marginal sea and gulf Ocean fringe versus coastal indentation
Memory Hook
Mediterranean salty, Baltic fresh, Red Sea splitting, Aral gone, Caspian shut.
Mains Angle
Questions mix location and issues. These points add depth.
- Salinity Evaporation versus inflow
- Human impact Aral Sea
- Law South China Sea
A Question You May Face
An original practice question, not a past paper question.
“Explain the variation of salinity among the Mediterranean, Black, Baltic and Red seas and discuss the geopolitical importance of any one sea.”
How to Answer
- Types Marginal, Mediterranean, inland.
- Salinity Evaporation and inflow.
- Issues Aral and Dead Sea.
- Geopolitics South China Sea.
GS Relevance
Frequently Asked Questions
What is a marginal sea?
A marginal sea is a part of an ocean that is partly enclosed by land, islands or an island arc, and lies mostly on the continental shelf. Examples are the East China Sea, South China Sea, North Sea and the Arabian Sea, where the water is shallower than in the open ocean.
Why is the Mediterranean Sea saltier than the Atlantic?
The Mediterranean has high evaporation under its hot, dry climate and receives little river water or rain. Its connection with the Atlantic at the Strait of Gibraltar is narrow, so the salty water cannot be diluted easily, and its salinity is about 38 parts per thousand.
Why is the Baltic Sea less salty?
The Baltic Sea receives large amounts of fresh water from many rivers and has low evaporation in its cool climate. Its connection to the North Sea through narrow Danish straits is shallow and limits the entry of salt water, so its salinity is only about 7 parts per thousand.
What happened to the Aral Sea?
The Aral Sea in Central Asia shrank to a small fraction of its former size from the 1960s because the Amu Darya and Syr Darya rivers were diverted to irrigate cotton. Fishing collapsed, salt storms rose from the dry bed, and the region faced an environmental and health crisis.
Why is the South China Sea important?
The South China Sea is one of the world's busiest trade routes, with rich fisheries and oil and gas reserves. Several countries claim its islands and waters, and a 2016 arbitral tribunal under UNCLOS ruled against China's historic claims, a ruling that China does not accept.
PYQ Practice — Statement Analysis
1 The Dead Sea shore is the lowest land point on Earth.
It lies over 400 m below sea level.
2 The Caspian Sea is connected to the Mediterranean by the Bosphorus.
The Caspian is landlocked; the Bosphorus links the Black Sea.
3 The Baltic Sea has lower salinity than the Mediterranean Sea.
River inflow dilutes it.
4 The Red Sea lies in a rift valley.
The African and Arabian plates are separating.
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