The major oceanic divisions
Oceans are divided into numerous regions depending on the physical and biological conditions of these areas. The pelagic zone includes all open ocean regions, and can be subdivided into further regions categorized by depth and light abundance. The photic zone covers the oceans from surface level to 200 meters down. This is the region where the photosynthesis most commonly occurs and therefore contains the largest biodiversity in the ocean. Since plants can only survive with photosynthesis any life found lower than this must either rely on material floating down from above (see marine snow) or find another primary source; this often comes in the form of hydrothermal vents in what is known as the aphotic zone (all depths exceeding 200m). The pelagic part of the photic zone is known as the epipelagic. The pelagic part of the aphotic zone can be further divided into regions that succeed each other vertically. The mesopelagic is the uppermost region, with its lowermost boundary at a thermocline of 12°C, which, in the tropics generally lies between 700 and 1,000 m. After that is the bathypelagic lying between 10°C and 4°C, or between 700 or 1,000 m and 2,000 or 4,000 m. Lying along the top of the abyssal plain is the abyssalpelagic, whose lower boundary lies at about 6,000 m. The final zone falls into the oceanic trenches, and is known as the hadalpelagic. This lies between 6,000 m and 10,000 m and is the deepest oceanic zone.
Along with pelagic aphotics zones there are also benthic aphotic zones, these correspond to the three deepest zones. The bathyal zone covers the continental slope and the rise down to about 4,000 m. The abyssal zone covers the abyssal plains between 4,000 and 6,000 m. Lastly, the hadal zone corresponds to the hadalpelagic zone which is found in the oceanic trenches. The pelagic zone can also be split into two subregions, the neritic zone and the oceanic zone. The neritic encompasses the water mass directly above the continental shelves, while the oceanic zone includes all the completely open water. In contrast, the littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions. It is also known as the intertidal zone because it is the area where tide level affects the conditions of the region.
Climate effects
One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called “typhoons” and “hurricanes” depending upon where the system forms). Ocean currents greatly affect the Earth’s climate by transferring warm or cold air and precipitation to coastal regions, where they may be carried inland by winds. The Antarctic Circumpolar Current encircles that continent, influencing the area’s climate and connecting currents in several oceans.
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III. Answer the questions:
1. What is oceanography?
2. How does the ocean and atmosphere link?
3. How many per cents of the Earth’s surface are covered by ocean?
4. What is the average salinity of the ocean?
5. What is the World Ocean?
6. How many oceans are there on the Earth?
7. Is the Great Salt Lake a part of the ocean? Why?
8. The Pacific Ocean is the largest ocean in the world, is not it? What are the others?
9. What is the deepest place in the ocean?
10. What is the reason of the blue color of the ocean water?
11. What is the ocean glow?
12. How many oceanic zones do you know? Make a list of them and give their brief description.
13. How do the oceans affect the climate of the Earth?
IV. Do you agree or disagree with the following statements? Prove your opinion.
1. Oceanography covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries.
2. An ocean is a major body of fresh water, and a principal component of the hydrosphere.
3. There is only one ocean on our planet.
4. The Indian Ocean is the largest and deepest ocean on the Earth.
5. The oceans cover ¾ of the earth’s surface and have great impact on the biosphere.
6. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth’s mantle where there are no continents.
7. Ocean water has blue color because it reflects the color of the sky.
8. Ocean does not have any glow.
9. Ocean is not divided into regions.
10. One of the most dramatic forms of weather phenomena occurs over the oceans: tropical cyclones.
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