Marginal seas are similar to open oceans with respect to being created by large-scale geological processes, exhibiting biodiversity , and possessing layered water circulation patterns. The degree of water circulation between marginal seas and open oceans varies with respect to location. The primary differences between marginal seas and open oceans are associated with depth and proximity to landmasses. Marginal seas, which are generally shallower than open oceans, are more influenced by human activities, river runoff, climate, and water circulation. Read the article below to get more information.


  • Marginal seas


marginal sea basin, also called a back-arc basin, is a series of small sea basins located between a continent and island arc or among island arcs . It is the product of secondary sea floor expanding in the back-arc region and has the slightly thick (< 20 km) oceanic crust as its basement.

The petrographic, geochemical, and evolutionary characteristics of tholeiitic rock in the marginal sea basin are all similar to those in the oceanic ridge, and the variation in geochemical characteristics depends on the following factors: partial melting level, homogeneous level of mantle source zone, and high crystallization differentiation level in the magmatic chamber

In addition, the fluid phase derived in the subducting plate may also be another important factor. The geochemical component of trace elements not only has the characteristics of MORB but also displays certain characteristics of island arc basalt. This shows that the component affected by subduction is involved in the formation of the basaltic magma in the expansion center of the marginal sea basin and thus characterizes this type of basalt as an island arc tholeiite. Usually, at the initial stage of extension of the marginal sea basin, the fluid phase derived in the course of subduction has the most important impact on the formation of magma. However, with the extension of the basin, its impact weakens gradually.

The plate motion is directly constrained by the deep action, and the volcanic eruption or intrusion is the performance of upper mantle and deep crust convection on the earth's surface or in the shallow crust. Therefore, different igneous rock associations or series and different rock geochemical characteristics are formed in different tectonic settings. It is important to study the distribution and characteristics of volcanic rock by taking the tectonic setting into consideration.


Marginal seas of the Arctic Ocean

  • Barents Sea
  • The Irish Sea

Marginal seas of the Atlantic Ocean

  • Argentine Sea
  • Caribbean Sea
  • English Channel
  • Gulf of Mexico
  • Hudson Bay
  • Irish Sea
  • Labrador Sea
  • Mediterranean Sea
  • North Sea
  • Norwegian Sea
  • Scotia Sea

Marginal seas of the Indian Ocean

  • Andaman Sea
  • Arabian Sea
  • Bay of Bengal
  • Java Sea
  • Persian Gulf
  • Red Sea
  • Sea of Zanj

Marginal seas of the Mediterranean Sea

Major conflict zones lie on the east of Mediterranean. Also recent refugee crisis is constantly in news. Hence the locations from the region are important for prelims.

  • Adriatic Sea
  • Aegean Sea

Marginal seas of the Pacific Ocean

  • Bering Sea
  • Celebes Sea
  • Coral Sea
  • East China Sea
  • Philippine Sea
  • Sea of Japan
  • Sea of Okhotsk
  • South China Sea (another important conflict zone)
  • Tasman Sea (between Australia and New Zealand)
  • Yellow Sea (by the Korean Peninsula)

Other seas

  • The Caribbean Sea is sometimes defined as a marginal sea, sometimes as a Mediterranean sea.
  • The Caspian Sea is also sometimes defined as a marginal sea, and also the Dead Sea.

The above article gives information on the marginal seas, which is a very important part of UPSC mains GS paper 1. To read more articles on geography click here