Marginal seas of the world

What are Marginal Seas? What is Phytoplankton Bloom (Algal Bloom) in Marginal Seas? How does water circulation happen in marginal seas? Read further to know more.

Marginal seas are more susceptible to pollution than open ocean regions because of the high concentration of human activities near coastlines and rivers. The greatest human impact on marginal seas is related to the fisheries industry.

Other human activities that have adversely affected marginal seas include industrial sewage disposal, offshore oil drilling, and accidental releases of pollutants, including petroleum products, radioactive waste, detergents, and plastics.

Also read: High Seas Treaty

What are Marginal Seas?

• In oceanography, a marginal sea is a sea partially enclosed by islands, archipelagos, or peninsulas.
• Some of the major marginal seas include the Arabian Sea, Baltic Sea, Bay of Bengal, Bering Sea, Black Sea, Gulf of California, Gulf of Mexico, Mediterranean Sea, Red Sea, and all four of the Siberian Seas (Barents, Kara, Laptev, and East Siberian).
• 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.

Important marginal seas in the world

Important marginal seas are mentioned below.

Marginal seas of the Arctic Ocean

Barents Sea

• The Barents Sea is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territorial waters.
• The Barents Sea is a rather shallow shelf sea, with an average depth of 230 meters

The Irish Sea

• The Irish Sea is an extensive body of water that separates the islands of Ireland and Great Britain.
• It is linked to the Celtic Sea in the south by St George’s Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Channel.

Marginal seas of the Atlantic Ocean

Argentine Sea

• The Argentine Sea is a marginal sea of the Atlantic Ocean adjacent to the southern tip of South America.
• It ranges from the mouth of the estuary of the Río de la Plata in the north to the Isla de los Estados in the south, and from the Argentine coast to the 200 meters isobath.

Caribbean Sea

• The Caribbean Sea is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere.
• It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles starting with Cuba, to the east by the Lesser Antilles, and to the south by the northern coast of South America. The Gulf of Mexico lies to the northwest.

English Channel

• The English Channel, also known as simply the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France.
• It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busiest shipping area in the world.

Gulf of Mexico

• The Gulf of Mexico is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent.
• It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southwest and south by the Mexican states of Tamaulipas, Veracruz, Tabasco, Campeche, Yucatan, and Quintana Roo; and on the southeast by Cuba.

Hudson Bay

• Hudson Bay sometimes called Hudson’s Bay, is a large body of saltwater in northeastern Canada with a surface area of 1,230,000 km² (470,000 sq mi).
• It is located north of Ontario, west of Quebec, northeast of Manitoba, and southeast of Nunavut, but politically entirely part of Nunavut. It is an inland marginal sea of the Arctic Ocean.

Irish Sea

• The Irish Sea is an extensive body of water that separates the islands of Ireland and Great Britain.
• It is linked to the Celtic Sea in the south by St George’s Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Channel. Anglesey, North Wales, is the largest island in the Irish Sea, followed by the Isle of Man. 

Labrador Sea

• The Labrador Sea is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelves to the southwest, northwest, and northeast.
• It connects to the north with Baffin Bay through the Davis Strait.

Mediterranean Sea

• The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin, and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and the east by the Levant.
• The Mediterranean has played a central role in the history of Western civilization. Geological evidence indicates that around 5.9 million years ago the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.

North Sea

• The North Sea lies between Great Britain, Denmark, Norway, Germany, the Low Countries, and France. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Sea in the north.
• It is more than 970 kilometers (600 mi) long and 580 kilometers (360 mi) wide, covering 570,000 square kilometers (220,000 sq mi).

Norwegian Sea

• The Norwegian Sea is a marginal sea, grouped with either the Atlantic Ocean or the Arctic Ocean, northwest of Norway between the North Sea and the Greenland Sea, adjoining the Barents Sea to the northeast.
• In the southwest, it is separated from the Atlantic Ocean by a submarine ridge running between Iceland and the Faroe Islands. To the north, the Jan Mayen Ridge separates it from the Greenland Sea.

Scotia Sea

• The Scotia Sea is a sea located at the northern edge of the Southern Ocean at its boundary with the South Atlantic Ocean. It is bounded on the west by the Drake Passage and on the north, east, and south by the Scotia Arc, an undersea ridge and island arc system supporting various islands.
• The sea sits atop the Scotia Plate. It is named after the expedition ship Scotia. Many icebergs melt there.

Marginal seas of the Indian Ocean

Andaman Sea

• The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and the west side of the Malay Peninsula and separated from the Bay of Bengal to its west by the Andaman Islands and the Nicobar Islands. Its southern end is at Breueh Island just north of Sumatra, with the Strait of Malacca further southeast.

Arabian Sea

• The Arabian Sea is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran, and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel, and the Arabian Peninsula, on the southeast by the Laccadive Sea and the Maldives, on the southwest by Somalia, and the east by India.
• Its total area is 3,862,000 km² (1,491,000 sq mi) and its maximum depth is 4,652 meters (15,262 ft). The Gulf of Aden in the west connects the Arabian Sea to the Red Sea through the strait of Bab-el-Mandeb, and the Gulf of Oman is in the northwest, connecting it to the Persian Gulf.

Bay of Bengal

• The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and the east by Myanmar and the Andaman and Nicobar Islands of India.
• Its southern limit is a line between Sangaman Kanda, Sri Lanka, and the northwesternmost point of Sumatra, Indonesia. It is the largest water region called a bay in the world.
• There are countries dependent on the Bay of Bengal in South Asia and Southeast Asia. During the existence of British India, it was named the Bay of Bengal after the historic Bengal region. At the time, the Port of Kolkata served as the gateway to the Crown’s rule in India.
• Cox’s Bazar, the longest sea beach in the world, and Sundarbans, the largest mangrove forest and the natural habitat of the Bengal tiger, are located along the bay.

Java Sea

• The Java Sea is an extensive shallow sea on the Sunda Shelf, between the Indonesian islands of Borneo to the north, Java to the south, Sumatra to the west, and Sulawesi to the east.
• Karimata Strait to its northwest links it to the South China Sea. It is a part of the western Pacific Ocean.

Persian Gulf

• The Persian Gulf sometimes called the Arabian Gulf is a Mediterranean sea in Western Asia. The body of water is an extension of the Arabian Sea located between Iran and the Arabian Peninsula.
• It is connected to the Gulf of Oman in the east by the Strait of Hormuz. The Shatt al-Arab River delta forms the northwest shoreline.

Red Sea

• The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab el Mandeb strait and the Gulf of Aden.
• To its north lie the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez (leading to the Suez Canal). It is underlain by the Red Sea Rift, which is part of the Great Rift Valley.

Sea of Zanj

• The Sea of Zanj is a former name for that portion of the western Indian Ocean adjacent to the region in the African Great Lakes referred to by medieval Arab geographers as Zanj.
• The Sea of Zanj was deemed a fearful zone by Arab mariners and legends regarding dangers in the waters abounded, especially near its far southern limits.

Marginal seas of the Mediterranean Sea

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

Adriatic Sea

• The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan Peninsula.
• The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to the northwest and the Po Valley.
• The countries with coasts on the Adriatic are Albania, Bosnia and Herzegovina, Croatia, Italy, Montenegro, and Slovenia.

Aegean Sea

• The Aegean Sea is an elongated embayment of the Mediterranean Sea between Europe and Asia. It is located between the Balkans and Anatolia and covers an area of some 215,000 square kilometers.
• In the north, the Aegean is connected to the Marmara Sea and the Black Sea by the straits of the Dardanelles and the Bosphorus. The Aegean Islands are located within the sea and some bound it on its southern periphery, including Crete and Rhodes.
• The sea reaches a maximum depth of 2,639m to the west of Karpathos. The Thracian Sea and the Sea of Crete are the main subdivisions of the Aegean Sea.

Marginal seas of the Pacific Ocean

Bering Sea

• The Bering Sea is a marginal sea of the Northern Pacific Ocean. It forms, along with the Bering Strait, the divide between the two largest landmasses on Earth: Eurasia and The Americas. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves. The Bering Sea is named after Vitus Bering, a Danish navigator in Russian service, who, in 1728, was the first European to systematically explore it, sailing from the Pacific Ocean northward to the Arctic Ocean.

Celebes Sea

• The Celebes Sea or Sulawesi Sea, of the western Pacific Ocean, is bordered on the north by the Sulu Archipelago and Sulu Sea and Mindanao Island of the Philippines, on the east by the Sangihe Islands chain, on the south by Sulawesi’s Minahasa Peninsula, and the west by northern Kalimantan in Indonesia.
• It extends 420 miles (675 km) north-south by 520 mi (840 km) east-west and has a total surface area of 110,000 square miles (280,000 km²), to a maximum depth of 20,300 feet (6,200 m). South of Cape Mangkalihat, the sea opens southwest through the Makassar Strait into the Java Sea.

Coral Sea

• The Coral Sea is a marginal sea of the South Pacific off the northeast coast of Australia and is classified as an interim Australian bioregion. The Coral Sea extends 2,000 kilometers (1,200 mi) down the Australian northeast coast.
• Most of it is protected by the French Natural Park of the Coral Sea and the Australian Coral Sea Marine Park. The sea was the location for the Battle of the Coral Sea, a major confrontation during World War II between the navies of the Empire of Japan, the United States, and Australia.

East China Sea

• The East China Sea is an arm of the Western Pacific Ocean, located directly offshore from East China. It covers an area of roughly 1,249,000 square kilometers (482,000 sq mi).
• The sea’s northern extension between mainland China and the Korean Peninsula is the Yellow Sea, separated by an imaginary line between the eastern tip of Qidong at the Yangtze River estuary and the southwestern tip of South Korea’s Jeju Island.

Philippine Sea

• The Philippine Sea is a marginal sea of the Western Pacific Ocean east of the Philippine archipelago (hence the name), the largest in the world, occupying an estimated surface area of 5 million square kilometers (2×10⁶ sq mi).
•  The Philippine Sea Plate forms the floor of the sea. Its western border is the first island chain to the west, comprising the Ryukyu Islands in the northwest and Taiwan in the west

Sea of Japan

• The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific Ocean.
• This isolation also affects faunal diversity and salinity, both of which are lower than in the open ocean. The sea has no large islands, bays, or capes. Its water balance is mostly determined by the inflow and outflow through the straits connecting it to the neighboring seas and the Pacific Ocean. Few rivers discharge into the sea and their total contribution to the water exchange is within 1%.

Sea of Okhotsk

• The Sea of Okhotsk is a marginal sea of the western Pacific Ocean. It is located between Russia’s Kamchatka Peninsula on the east, the Kuril Islands on the southeast, Japan’s island of Hokkaido on the south, the island of Sakhalin along the west, and a stretch of eastern Siberian coast along the west and north.
• The northeast corner is the Shelikhov Gulf. The sea is named after the Okhota River, which is in turn named after the Even word (okat) meaning “river”.

South China Sea

• The South China Sea, or South East Asian Sea, is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Philippines, and in the south by Borneo, eastern Sumatra, and the Bangka Belitung Islands, encompassing an area of around 3,500,000 km² (1,400,000 sq mi).
• It communicates with the East China Sea via the Taiwan Strait, the Philippine Sea via the Luzon Strait, the Sulu Sea via the straits around Palawan (e.g. the Mindoro and Balabac Straits), the Strait of Malacca via the Singapore Strait, and the Java Sea via the Karimata and Bangka Straits.

Tasman Sea

• The Tasman Sea is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand.
• It measures about 2,000 km (1,200 mi) across and about 2,800 km (1,700 mi) from north to south.
  

Yellow Sea

• The Yellow Sea is a marginal sea of the Western Pacific Ocean located between mainland China and the Korean Peninsula and can be considered the northwestern part of the East China Sea.
• It is one of four seas named after common color terms (the others being the Black Sea, the Red Sea, and the White Sea), and its name is descriptive of the golden-yellow color of the silt-ridden water discharged from major rivers.

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.

Phytoplankton Bloom (Algal Bloom) in Marginal Seas

• The Mediterranean Sea and the Black Sea are marginal seas found in proximity to one another. The color difference shown here is due to a phytoplankton bloom occurring in the Black Sea.
• Phytoplankton is good as fish feed on them. But when they proliferate indiscriminately, they consume too much oxygen during the night, thus depriving other marine organisms of oxygen.
• For example, the discharge of domestic sewage leads to elevated nutrient concentrations (particularly phosphates) which can result in harmful algal blooms.

Biomass Production and Primary Productivity

• Marine biomass production originates with primary productivity, which in turn is affected by the availability of sunlight, carbon dioxide, nutrients such as nitrates and phosphates, and trace elements.
• Marginal seas generally exhibit intermediate levels of primary production, with the highest rates found in coastal upwelling regions and the lowest primary production occurring in open ocean regions.
• Hence, the highest biomass production rates occur in coastal upwelling zones, the lowest in open ocean regions, and intermediate rates in marginal seas.
• For near-shore regions, the dominant processes influencing primary productivity are river runoff, water column mixing, and turbidity.
• River runoff and water column mixing introduce dissolved nutrients, trace elements, and suspended particles into the photic (light) zones of near-shore regions.
• Although the addition of dissolved nutrients and trace elements to coastal waters and marginal seas serves to increase primary production, the addition of suspended particles increases water turbidity, which results in reduced sunlight penetration and decreased primary productivity.

Water Circulation in Marginal Seas

• Water circulation patterns in marginal seas depend largely on the shape of the sea, fresh-water input (e.g., river runoff and precipitation), and evaporation.
• If river runoff and precipitation exceed evaporation, as is the case in the Black and Baltic Seas, the excess fresh water will tend to flow seaward near the sea surface.
• If evaporation exceeds river runoff and precipitation, as in the Mediterranean Sea, the marginal sea water becomes saltier, then sinks and flows towards the less salty open ocean region.

Bays, gulfs, and Straits

• Bays, gulfs, and straits are types of water bodies that are contained within a larger body of water near land.
• These three water bodies are usually located at important points of human activities; thus, conflicts with nature and neighbors are common.

Bays

• A bay is a small body of water that is set off from a larger body of water generally where the land curves inward.
• In simple words, a bay is a water body surrounded on three sides by land with the fourth side (mouth) wide open towards oceans. (In Gulfs, the mouth is narrow).
• A bay is usually smaller and less enclosed than a gulf.
• Examples: The Bay of Pigs (Cuba), Hudson Bay (Canada), Bay of Bengal, etc.
• An example of a bay at a river’s mouth in New York Bay, at the mouth of the Hudson River (Hudson Estuary).

Guantánamo Bay

• Guantánamo Bay is a sheltered inlet within the Caribbean Sea.
• During the Spanish-American War in 1898, the United States gained access to the outer harbor of Guantánamo Bay.
• Through an agreement signed with Cuba in 1903, the United States obtained the right to maintain a naval base at Guantánamo Bay.
• In 1934, a treaty reaffirmed the U.S. right to lease the site. The treaty gave the United States a perpetual lease on Guantánamo Bay.
• The most infamous Guantánamo Bay prison is here.

Gulfs

• A gulf is a large body of water, sometimes with a narrow mouth, that is almost surrounded by land. The world’s largest gulf is the Gulf of Mexico.
• Examples of other gulfs include the Gulf of California, the Gulf of Aden (between the Red Sea and the Arabian Sea), and the Persian Gulf (between Saudi Arabia and Iran).
• The Persian Gulf is important concerning world energy because petroleum is transported through its waters in oil tankers.

Straits

• A strait is a narrow passageway of water, usually between continents or islands, or between two larger bodies of water.
• The Strait of Gibraltar is probably the world’s most famous strait. It connects the Atlantic Ocean on its west with the Mediterranean Sea on its east.
• Two other well-known straits are the Strait of Bosporus and the Strait of Hormuz.
• The Strait of Bosporus connects the Black Sea (from the north) and the Sea of Marmara (from the south), and splits northwestern Turkey.
• The Strait of Hormuz is located at the southeastern end of the Persian Gulf. It is a narrow waterway that can be (and has been) controlled to prevent ships from sailing through the gulf.

Choke Point

• When a body of water such as a strait is capable of being blocked or even closed to control transportation routes, the body is called a “choke point.”
• Historically, the Strait of Gibraltar has been one of the world’s most important choke points.
• However, the Strait of Hormuz has become an important choke point in recent years because of increasing Middle East tensions.
• The Strait is surrounded by the United Arab Emirates Oman (on one side) and Iran (on the other side).

Isthmus

• The isthmus is the land equivalent of a strait. i.e., a narrow strip of land connecting two larger land masses.
• Example: Isthmus of Panama and Isthmus of Suez.

Article written by Aseem Muhammed