Oceans

• Hydrosphere – An Introduction
• Oceans – An Introduction
• Marginal seas of the world
• Bay, Gulf, Strait, Isthmus
• Law of the Sea

Hydrosphere – An Introduction

• The hydrosphere is the combined mass of water found on, under, and above the surface of a planet, minor planet or natural satellite.
• Approximately 71% of Earth’s surface, an area of some 361 million square kilometers is covered by ocean. 29% of Earth’s surface
• An area of some 148.89 million square kilometers is covered by land.
• It has been estimated that there are 1,386 million cubic kilometres of water on Earth.
• The total mass of the Earth’s hydrosphere is about 1.4 × 1018 tonnes, which is about 0.023% of Earth’s total mass.
• At any given time, about 20 × 1012 tonnes of this is in the form of water vapor in the Earth’s atmosphere (for practical purposes, 1 cubic meter of water weighs one tonne). The average salinity of Earth’s oceans is about 35 grams of salt per kilogram of seawater (3.5%).

Distribution of Water on the Earth’s Surface

• The distribution of water on the Earth’s surface is extremely uneven.
• Only 3% of water on the surface is fresh; the remaining 97% resides in the ocean.
• Of freshwater, 69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and swamps. Looked at another way, only one percent of the water on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.
• All one needs to do is study rainfall maps to appreciate how uneven the distribution of water really is. The white areas on the map below had annual rainfall under 400 mm for the last year, which makes them semi-arid or arid. And, remember, projections are for significant aridification to occur in many dry regions and for more severe rainfall events to characterize wet regions.

Commonly known as the water cycle. It is the circular flow of water within earth’s atmosphere, involving all the three forms of matter such as solid, liquid and gaseous forms. It also refers to the continuous exchange of water from the one form to another with the application of external energy. Through various process of physical action such as evaporation, condensation, precipitation, interception, infiltration, runoff, surface flow.

• Evaporation is the process of transformation of water from the water bodies to water vapour in the atmosphere.
• Condensation is the process of changing the state from water vapour to water in the upper air. It generally takes the form of cloud.
• Precipitation is the downpour of condensed cloud mostly in the form of rainfall, and sometimes as snow, hails, fog, drop, etc.
• Infiltration is the process of penetration of water into underground strata of earth’s crust.

Interception is the precipitation trapped by vegetation instead of falling on ground.

Run off is the movement of water on the earth, surface through different channels such as river, streams, etc.

Subsurface Flow is the movement of water within the earth’s crust after infiltration which eventually either come up through artesian well or seep to the ocean.

In the hydrologic cycle, water is transferred between the land surface, the ocean, and the atmosphere.

Encyclopædia Britannica, Inc.

Oceans – An Introduction

39.3% of the northern hemisphere comprises of landmass and 60.7% is covered by sea and oceans. This share in the southern hemisphere is of 19.1% and 80.9% between land and water.

An ocean is a body of water that composes much of a planet’s hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans.

As the world ocean is the principal component of Earth’s hydrosphere, it is integral to life, forms part of the carbon cycle, and influences climate and weather patterns. The World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger, possibly over two million.

Oceanic divisions

Oceanic Zones – Vertical

Marginal seas

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

Arctic Ocean

• • Barents Sea
  • The Irish Sea

Indian Ocean

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

Mediterranean Sea

• 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.

Major Trenches and Ridges in World

Mariana Trench

The cavity located near the Mariana Islands, where the Pacific Plate and the Philippine Plate converge; it is the world’s deepest trench (about 36,000 feet).

Puerto Rico Trench

It is located off the coast of Puerto Rico, on the boundary between the South American and Caribbean plates; it features the deepest point in the Atlantic Ocean (27,493 feet).

Peru-Chile Trench

The trench (26,460 feet) borders South America and it is the world’s longest trench (3,700 mi), located on the boundary between the Nazca Plate and the South American Plate.

Pacific-Antarctic Ridge

Mountain range separating the Pacific and Antarctic plates; it joins the eastern Pacific Ridge off the coast of South America.

East Pacific Ridge

Ridge that marks the boundary between the Pacific and Cocos Islands plates to the north, and the Pacific and Nazca plates to the south.

Aleutian Trench

Trench (25,600 feet) extending from Alaska to the Kamchatka Peninsula; it results from the Pacific Plate sliding beneath the

North American Plate.

North America

Its area (9.3 million sq. mi) represents about 16% of the world’s land; the Central American isthmus is an extension of North America.

Mid-Indian Ridge

Mountain range in the middle of the Indian Ocean that separates the African and Australian-Indian plates.

southwest Indian Ridge

Ridge separating the African and Antarctic plates; it joins the Mid-Indian and Southeast Indian ridges off the coast of Madagascar.

South America

Represents about 12% of the world’s land and is linked to North America by Central America; its features include the Andes in the west and plains and plateaus in east and central regions.

Mid-Atlantic Ridge

Ridge about 7,000 miles long, located in the middle of the Atlantic Ocean; some of its mountains reach the surface, forming islands such as Iceland.

Ryukyu Trench

Trench (24,629 feet) located near the Ryukyu Islands; it marks the boundary between the Philippine Plate and the Eurasian Plate.

Japan Trench

Trench (27,929 feet) located east of Japan, on the boundary between the Pacific Plate and the Eurasian Plate; this zone is marked by intense seismic activity

Kuril Trench

Trench (34,587 feet) located northeast of Japan; it results from the Pacific Plate sliding beneath the Eurasian Plate.

Philippine Trench

Trench bordering the eastern Philippines, reaching depths of 34,578 feet; it results from the Philippine Plate sinking beneath the Eurasian Plate.

Kermadec-Tonga Trench

Cavity located north of New Zealand, where the Pacific Plate meets the Australian-Indian Plate; it reaches depths of 35,702 feet.

Southeast Indian Ridge

Ridge separating the Antarctic Plate from the Australian-Indian Plate; its topography is more regular than the topography of the Southwest Indian and Mid-Indian ridges.

Java Trench

Trench located south of Indonesia, between the Australian-Indian and the Eurasian Plates; it is the deepest point in the Indian Ocean (24,440 ft).

Bay – A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay.

Examples- The Bay of Pigs (Cuba), Hudson Bay (Canada), Bay of Bengal Guantánamo Bay

Gulf – A gulf is a large inlet from the ocean into the landmass, typically with a narrower opening than a bay.Many gulfs are major shipping areas, such as the Persian Gulf, Gulf of Mexico, and Gulf of Aden.

Examples- Gulf of Mexico. The world’s largest gulf , Gulf of California, Gulf of Aden, Persian Gulf

• Strait – a narrow area of water connecting two wider areas of water. Examples – The Strait of Gibraltar, Strait of Bosporus, Strait of Hormuz.
• Fjord – a long bay with steep sides, typically formed by a glacier.
• Bight – a bight is a bend or curve in a coastline, river, or other geographical feature. It typically indicates a large, open bay, often only slightly receding bay that is typically shallower than a sound.
• Sound – A sound is often formed by the seas flooding a river valley. This produces a long inlet where the sloping valley hillsides descend to sea-level and continue beneath the water to form a sloping sea floor. The Marlborough Sounds in New Zealand are a good example of this type of formation.
• Cove – A cove is a small type of bay or coastal inlet. Coves usually have narrow, restricted entrances, are often circular or oval, and are often situated within a larger bay.
• Isthmus – 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.
• Law of the Sea

The United Nations Convention on the Law of the Sea is considered the “constitution of the oceans”. It is also known as the Law of the Sea Convention or the Law of the Sea treaty. It was open for signature at Montego Bay, Jamaica, on 10 December 1982 but entered into force on 14 November 1994 and is presently binding for 154 States, as well as the European Community

Provision of the Law of the Sea Convention The Law of the Sea Convention introduced a number of provisions and covered the most significant issues such as setting limits, navigation, archipelagic status and transit regimes, exclusive economic zones, jurisdiction of continental shelf, deep seabed mining, the exploitation regime, protection of the marine environment, scientific research, and settlement of disputes.

1. Internal waters: According to this treaty, country can make laws without interference of the alien country; regulate its use and use of its resources. Foreign vessels have no right of passage within internal waters without permission. 

2. Territorial waters: This convention defined the territorial water baseline as 12 Nautical miles (22.224 Kilometers) in which parent country is free to set laws, regulate use and use of its resources. Alien vessel are not allowed to enter within the territorial water baseline without permission except innocent passage (Innocent passage” is defined by the convention as passing through waters in an expeditious and continuous manner, which is not “prejudicial to the peace, good order or the security” of the coastal state.) 

3. Archipelagic waters: According to this convention, States consisting of archipelagos, provided certain conditions are satisfied, can be considered as “archipelagic States”, the outermost islands being connected by “archipelagic baselines” so that the waters inside these lines are archipelagic waters.

4. Exclusive Economic Zone: According to this convention, a 200-mile (370.4 km.) exclusive economic zone including the seabed and the water column, may be established by coastal States in which such States exercise sovereign rights and jurisdiction on all resource-related activities, including artificial islands and installations, marine scientific research and the protection of the environment; other States enjoy in the exclusive economic zone high seas freedoms of navigation, overflight, laying of cables and pipelines and other internationally lawful uses of the sea connected with these freedoms; a rule of reciprocal “due regard” applies to ensure compatibility between the exercise of the rights of the coastal States and of those of other States in the exclusive economic zone. 5. Continental Shelf: This convention defined the external limits of the continental shelf which may exceed 200 nautical miles until the natural prolongation ends. However, it may never exceed 350 nautical miles from the baseline; or it may never exceed 100 nautical miles beyond the line connecting the depth of 2,500 meters. Coastal states have the right to use mineral and non-living material in the subsoil of its continental shelf, to the exclusion of others.

6. Contiguous zone: The area of the 12 Nautical miles (22.224 km) beyond the territorial waters baseline is called Contiguous zone. According to the convention, beyond the 12-nautical-mile (22 km) limit, there is a further 12 nautical miles (22 km) from the territorial sea baseline limit, the contiguous zone. The countries that coming within the ambit of this zone can enforce laws only in four areas, i.e. Pollution, taxation, customs and immigration.

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Oceans Floor

Ocean Basin

Ocean Basin- Introduction Major Ocean Relief Features

Continental Shelf Continental Slope Continental Rise Deep Sea Plain or Abyssal Plain

Minor Ocean Relief Features

Ridges , Hills Seamounts Guyots Trenches Canyons Sleeps Fracture zones Island arcs Atolls Coral reefs Submerged volcanoes Sea-scarps

Ocean Relief – Introduction

In hydrology, an oceanic basin may be anywhere on Earth that is covered by seawater but geologically ocean basins are large geologic basins that are below sea level.

Continental Shelf

• A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea. Much of the shelves were exposed during glacial periods and interglacial periods.
• Continental Shelf of all oceans together cover 8.6% of the total area of the oceans basins.
• Gradient of continental is of 1° to 3°.
• Continental shelves are much narrow or absent in some continents, particularly where Fold Mountains run parallel or close to the coast.
• In Atlantic Ocean it is 2 km to 80 km wide.
• The continental shelf in Pacific Ocean varies between 160 km to 1600 km of width.
• On an average continental shelf of Indian ocean in the west is 640 km wide and in the east near Java and Sumatra is as narrow as 160 km and further narrower along the coast of Antarctic.
• The depth usually ranges from 120 to 370 meters from the surface water.
• Their width also varies from a few kilometers to more than 100 kilometers.
• This variation can be seen even in the context of the Indian peninsula. The continental shelf of the western coast of India is much wider than that of the eastern coast.
• Continental Shelves are of greater importance to man. They are the sources of fishes, minerals including sand and gravel, etc.
• A large quantity of world’s petroleum and natural gas are obtained from the shelves.
• Coral reefs are also common on continental shelves.
• The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents. However, little of the sediment is from current rivers; some 60–70% of the sediment on the world’s shelves is relict sediment, deposited during the last ice age, when sea level was 100–120 m lower than it is now.
• One of the striking features of the continental shelf is the presence of submarine canyons which extend to the continental slope.
• These canyons are ‘steep-sided valleys’ cut into the floor of the seas.
• They are very similar to the gorges found on the continents.
• One of the reasons for the formation of the submarine canyon is the underwater landslide.
• The continental shelf is generally considered to be territorial water extents of the nations to which it adjoins.

The continental slope

• Continental slope, seaward border of the continental shelf.
• The world’s combined continental slope has a total length of approximately 300,000 km and descends at an angle ranges 2-5° from the shelf break at the edge of the continental shelf to the beginning of the ocean basins at depths of 100 to 3,200 metres.
• The continental slope boundary indicates the end of the continents. Canyons and trenches are observed in this region.
• They have very little deposits of sediments on them due to their steepness and increasing distance from the land. Sea life is also far less here than on the shelf.
• The base of the continental slope will have deposits of sediments. This belt of sedimentary deposits forms the Continental Rise.
• When the slope reaches a level of between 0.5° and 1°it is referred to as the continental rise. With increasing depth the rise becomes virtually flat and merges with the abyssal plain.

Deep Sea Plain or Abyssal Plain

• Deep sea planes are gently sloping areas of the ocean basins.
• These are the flattest and smoothest regions of the world because of terrigenous and shallow water sediments that buries the irregular topography.
• It covers nearly 40% of the ocean floor.
• The depths vary between 3,000 and 6,000 m.
• The sediments which are formed from the remains of living things are called Oozes.
• Oozes can be seen in those seas which favour an abundant growth of organisms.
• Another type of sediments is red clay which is of volcanic origin or made up of tiny particles brought by wind and rivers.

Some relief feature seen on abyssal plains are: a. Submarine Ridges

• • The oceanic mountains are called as submarine ridges.
  • They are linear belts occurring near the middle of the oceans and are also called mid-oceanic ridges. The oceanic ridge is the site of frequent earthquakes. Volcanism is common in ocean ridges and it produces many relief features.
  • The Mid-Atlantic Ridge is the largest continuous submerged mountain ridge which runs from north to south in the Atlantic Ocean.
  • At some places, the peaks rise above the sea surface to form Islands.

b. Seamounts and Guyots

• Submerged volcanoes with sharp tops are called as seamounts.
• Sometimes they rise above the sea as isolated islands.
• Hawaii and Tahiti Islands are such exposed tops of volcanoes.
• Seamounts with a flattened top are called as Guyots or Tablemounts.

Major Trenches and Ridges in World

Mariana Trench

The cavity located near the Mariana Islands, where the Pacific Plate and the Philippine Plate converge; it is the world’s deepest trench(about 36,000 feet).

Puerto Rico Trench

It is located off the coast of Puerto Rico, on the boundary between the South American and Caribbean plates; it features the deepest point in the Atlantic Ocean (27,493 feet).

Peru-Chile Trench

The trench (26,460 feet) borders South America and it is the world’s longest trench (3,700 mi), located on the boundary be tween the Nazca Plate and the South American Plate.

Pacific-Antarctic Ridge

Mountain range separating the Pacific and Antarctic plates; it joins the eastern Pacific Ridge off the coast of South America.

East Pacific Ridge

Ridge that marks the boundary between the Pacific and Cocos Islands plates to the north, and the Pacific and Nazca plates to the south.

Aleutian Trench

Trench (25,600 feet) extending from Alaska to the Kamchatka Peninsula; it results from the Pacific Plate sliding beneath the North American Plate.

North America

Its area (9.3 million sq. mi) represents about 16% of the world’s land; the Central American isthmus is an extension of North America.

Mid-Indian Ridge

Mountain range in the middle of the Indian Ocean that separates the African and Australian-Indian plates.

Southwest Indian Ridge

Ridge separating the African and Antarctic plates; it joins the Mid-Indian and Southeast Indian ridges off the coast of Madagascar.

South America

Represents about 12% of the world’s land and is linked to North America by Central America; its features include the Andes in the west and plains and plateaus in east and central regions.

Mid-Atlantic Ridge

Ridge about 7,000 miles long, located in the middle of the Atlantic Ocean; some of its mountains reach the surface, forming islands such as Iceland.

Ryukyu Trench

Trench (24,629 feet) located near the Ryukyu Islands; it marks the boundary between the Philippine Plate and the Eurasian Plate.

Japan Trench

Trench (27,929 feet) located east of Japan, on the boundary between the Pacific Plate and the Eurasian Plate; this zone is marked by intense seismic activity.

Kuril Trench

Trench (34,587 feet) located northeast of Japan; it results from the Pacific Plate sliding beneath the Eurasian Plate.

Philippine Trench

Trench bordering the eastern Philippines, reaching depths of 34,578 feet; it results from the Philippine Plate sinking beneath the Eurasian Plate.

Kermadec-Tonga Trench

Cavity located north of New Zealand, where the Pacific Plate meets the Australian-Indian Plate; it reaches depths of 35,702 feet.

Southeast Indian Ridge

Ridge separating the Antarctic Plate from the Australian-Indian Plate; its topography is more regular than the topography of the Southwest Indian and Mid-Indian ridges.

Java Trench

Trench located south of Indonesia, between the Australian-Indian and the Eurasian Plates; it is the deepest point in the Indian Ocean (24,440 ft).

Submarine Canyons CANYON: a deep gorge, especially one with a river flowing through it GORGE: a steep, narrow valley or ravine VALLEY: a low area between hills or mountains or a depression, typically with a river or stream flowing through it.

• These are deep valleys, some comparable to the Grand Canyon of the Colorado river.
• They are sometimes found cutting across the continental shelves and slopes, often extending from the mouths of large rivers.
• The Hudson Canyon is the best known canyon in the world.

Broadly, there are three types of submarine canyons—

• Small gorges which begin at the edge of the continental shelf and extend down the slope to very great depths, e.g., Oceanographer Canyons near New England.
• Those which begin at the mouth of a river and extend over the shelf, such as the Zaire, the Mississippi and the Indus canyons.
• Those which have a dendritic appearance and are deeply cut into the edge of the shelf and the slope, like the canyons off the coast of southern California. The Hudson Canyon is the best known canyon in the world. The largest canyons in the world occur in the Bering Sea off Alaska. They are the Bering, Pribilof and Zhemchung canyons.

Bank

• These marine features are formed as’ a result of erosional and depositional activity.
• A bank is a flat topped elevation located in the continental margins.
• The depth of water here is shallow but enough for navigational purposes.
• The Dogger Bank in the North Sea and Grand Bank in the north-western Atlantic, Newfoundland are famous examples.
• The banks are sites of some of the most productive fisheries of the world. Shoal A shoal is a detached elevation with shallow depths. Since they project out of water with moderate heights, they are dangerous for navigation.

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