In the previous post, we have read regionalisation of the Oceans, on the following basis,
- Penetration of Sun Rays and
- Based on Bioproductivity.
Now, in this post, we will study the other two classifications, based on,
- Ecological Division of Oceans or Depth wise division and
- Morphological Division or Structure of the Oceans Basin.
Ecological Division of Oceans
On the basis of depth, oceans are divided into the following regions,
- Pelagic Zone,
- Neritic Zone,
- Littoral Zone,
- Sub-Littoral Zone,
- Benthic Zone and
- Abyssal and Hadal Zone.
The word Pelagic means, relating to open sea. This zone includes the Neritic Zone as well. But it must express the high ocean which is a nearly biological desert. One can find some migratory species like Salmon, Whale, Shark and other mammals.
90% of the Biomass and Bio-Productivity can be found in the Neritic Zone of the Ocean. This region is found over Continental Shelf because of this it has terrestrial minerals.
Because of the maximum Solar energy intake, this zone provides favourable conditions to phytoplankton to thrive. This region is also called as Green Pastures of Oceans because of the phytoplanktons.
The zone between High Water Tide and Low Water Tide is Littoral Zone. So, the region has Oysters, Crabs, Prawn and Turtle marine species.
The Sub-Littoral Zone exists up to the depth of 100 meters. Benthic are the main species of this zone. Example- Sea-Crabs, Corals, Sea Sponge.
In this zone of the ocean, Sunrays doesn’t penetrate. So, photosynthesis is not possible here. Life in this region is because of the Chemosynthesis process.
Abyssal and Hadal Zone
This is the biological desert zone of the Oceans. This is the deepest part of the ocean.
Morphological Division of the Oceans
On the basis of the Oceanic crust shape, Oceans are divided into the following zones,
- The Continental Shelf,
- Continental Slope,
- Continental Rise and
- Abyssal Plains
So, the Continental Shelves, Continental Slop and Continental Rise occupy 27, 28 and 19 million square km of the area respectively.
Continental Shelf of the Oceans
Continental Shelves are the submerged part of the Continental Margins. It extends up to 200m depth. Its average width is 70km. The mean slope is less than 1°. It covers about 7.5% of the total area of the oceans.
The Continental Shelf zone is a Photic Zone of the Ocean. It has the highest biodiversity. This region is mineral-rich and has 90% of marine lives. This is the most significant part of the Oceans.
This zone is widest along with the stable coastlines and narrowest along with the mountain ranges mainly Fold Mountains. The widest Continental Shelves are found in 45°-65°N latitudes. It is specifically along the external part of the continents.
It is because, during Ice-age, continents buried under the ice (below sea level). So, now when ice has melted, the submerged continents are growing.
Continental Slope of the Oceans
It covers around 8.5% of the Ocean bottom area. Continental Slopes are the product of erosional forces. They have mobile sediments. Because of these mobile sediments, slopes have been building up. The average gradient of the slope is about 4°.
The Continental Rise is depositional features of the Oceans. Its slope angle is 0.5°. The Continental Rise have both terrestrial and submarine deposits. But marine deposits dominate in this region.
This zone is a transitional zone, where Continental margins ends and Continent meets Oceanic currents. It extends up to 400m and the Oceanic Trenches are located along the Continental Margins.
It covers 40% of the Ocean floor. It is a flat rolling plain with a thick mantle of deposits. Its general slope is 1/1000. Abyssal Plain is composed of Basaltic Crust. And Abyssal Plains are highly dynamic as seafloor is spreading.
So, this was all about the Division of the oceans. In the upcoming posts, we will study the Salinity and Salt Budget of the Oceans.
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