Ocean & Ocean Water (Temperature & Salainity)

 Hydrological Cycle

• The circulation of water within the earth’s hydrosphere in different forms i.e. the liquid, solid and the gaseous phases.
• Nearly 59 per cent of the water that falls on land returns to the atmosphere through evaporation from over the oceans as well as from other places.

Relief of The Ocean Floor

• Major portion of the ocean floor is found between 3-6 km below the sea level.
• Floors of the oceans are rugged with the world’s largest mountain ranges, deepest trenches and the largest plains.

Divisions of the Ocean Floors

Continental Shelf

• Occupied by relatively shallow seas and gulfs.
• Gradient of 1° or even less.
• Shelf break – Shelf break at very steep slope.
• Average width: About 80 km. shelves are almost absent or very narrow along some of the margins like the coasts of Chile, the west coast of Sumatra, etc.
• Siberian shelf in the Arctic Ocean – 1500 km & depth 30m (some area deep as 600m).
• Massive sedimentary deposits received over a long time by the continental shelves, become the source of fossil fuels.

Continental Slope

• Connects the continental shelf and the ocean basins. Depth 200 – 3,000m.
• Sharply drops off into a steep slope of gradient between 2 – 5^o.
• Deep Sea Plain/ Abyssal Plain
• Flattest & Smoothest regions of the world. Depth 3,000 and 6,000m.
• Fine-grained sediments like clay and silt.

Oceanic Deeps or Trenches

• Deepest parts of the oceans. 3-5 km deeper than surrounding.
• Occur at the bases of continental slopes and along island arcs and are associated with active volcanoes and strong earthquakes.
• 57 Deeps explored: 32 Pacific Ocean, 19 Atlantic Ocean & 6 Indian Ocean.

Minor Relief Features

Mid-Oceanic Ridges

• Two chains of mountains separated by a large depression.
• Peak high as 2,500m, Some even reach above the ocean’s surface.
• Ex: Ireland in Mid-Atlantic Ridge.

Seamount

• Mountain with pointed summits, rising from the seafloor that does not reach the surface of the ocean.
• volcanic in origin. 3,000 – 4,500m tall.
• Hawaiian Islands in the Pacific Ocean.

Submarine Canyons

• Deep valleys. comparable to the Grand Canyon of the Colorado river.
• Cutting across the continental shelves and slopes.
• Ex: Hudson Canyon.

Guyots

• Flat topped seamount.
• 10,000 seamounts and guyots exist in the Pacific Ocean alone.

Atoll

• Low islands found in the tropical oceans consisting of coral reefs surrounding a central depression. Part of sea (lagoon) or enclosing a body of fresh, brackish, or highly saline water.

Temperature of Ocean water

• Process of heating and cooling of the oceanic water is slower than land.

Factors Affecting Temperature Distribution.

1. Latitude - amount of insolation decreases poleward.
2. Unequal distribution of land and water – Northern Hemisphere (Extend land) more heat than Southern Hemisphere.
3. Prevailing wind – longitudinal variation in the temperature. onshore winds pile up warm water near the coast and this raises the temperature.
4. Ocean currents - warm ocean currents raise the temperature in cold areas while the cold currents decrease the temperature in warm ocean areas.

Horizontal and Vertical Distribution of Temperature

• Temperature decreases with the increasing depth.
• First layer - 500m thick with temperatures ranging between 20° and 25° C. layer within the tropical region.
• Second Layer or thermocline - rapid decrease in temperature with increasing depth. The thermocline is 500 -1,000 m thick.
• Third layer - very cold and extends upto the deep ocean floor. Artic & Antarctic Circle.
• Rate of decrease of temperature with increasing latitude is generally 0.5°C per latitude.
• Average temperature - 22°C at 20° latitudes, 14° C at 40° latitudes and 0° C near poles.
• Highest temperature record in Northern Hemisphere not in equator. Becaude of high land in NH.
• Average annual temperature of Northern Hemisphere – 19° C & Southern Hemisphere – 16° C.
• The temperature falls very rapidly up to the depth of 200 m and thereafter, the rate of decrease of temperature is slowed down.

Salinity of Ocean Waters

• Salinity is the term used to define the total content of dissolved salts in sea water.
• Amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.
• Expressed in parts per thousand [ ‰] or ppt.
• Salinity of 24.7 ‰ has been considered as the upper limit to demarcate ‘brackish water’.

Factors affection Ocean Salinity

• Evaporation and precipitation.
• Coastal regions by the fresh water flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
• Wind, transferring water to other areas.
• Ocean Current, any change in the temperature or density influences the salinity of water in an area.
• Highest salinity in water bodies
• Lake Van in Turkey (330 ‰)
• Dead Sea (238 ‰),
• Great Salt Lake (220 ‰)

Horizontal Distribution of Salinity

• Normal open ocean 33 ‰ – 37 ‰. Land locked res sea 41‰.
• Estuaries and the Arctic 0 - 35‰.
• evaporation is high, the salinity sometimes reaches to 70 ‰.
• Pacific Ocean, variation of salinity because of large size. Atlantic Ocean is around 36 ‰.
• Salinity decrease from 35‰ - 31‰ on the western part of NH (influx of melting water). Same way after 15° – 20° South, decrease to 33‰.
• Highest salinity 15° – 20° latitude.
• Maximum salinity (37 ‰) is observed between 20° N and 30° N and 20° W - 60° W.
• Indian Ocean - 35 ‰ (Bay of Bengal – Low salinity & Arabian sea – High Salinity).

Vertical Distribution of Salinity

• Salinity at depth is very much fixed, because there is no way that water is ‘lost’, or the salt is ‘added.
• Lower salinity water rests above the higher salinity dense water.
• Salinity, generally, increases with depth and there is a distinct zone called the halocline.