Oceans cover about 71% of our planet surface and support the greatest ecosystems of the Earth. Oceans play a major role for the preservation of life in our planet and as such its knowledge is essential. In order to implement effective conservation measures it is necessary to know the life that the ocean hosts as well as its dynamics.
The average depth of the ocean basin is of about 3500 m, while the mean height of land above sea level is around 800 m. However, the deepest location in the ocean reaches a bit more than 11000 m and is located in the Pacific Ocean – the Mariana trench.
The ocean floor feature a series of physiogeographic characteristics related to the geodynamic of our planet. Thus, the oceanic topography presents five main forms – continental shelf, continental slope, abyssal plain, trenches and oceanic ridge or rise.
Both continental shelf and continental slope correlate to the portion of continents that is submerged. The first begins at the coastline and descends with a gentle slope to an average depth of 200-300 m.
The continental shelf follows the continental slope (3000-4000 m deep) where the slope is more pronounced and marks the transition to the oceanic crust. The abyssal Plains are flat regions that lie between 4000 m and 6000 m deep.
The oceanic ridges are divergent plate boundary zones where there is realease of magma and, consequently, formation of new oceanic crust.
Finally, the oceanic pits are large depressions that form in the limits of converging plates, where there is plaque destruction. These have very steep slopes and extend to depths exceeding 6000 m.
The marine environment can also be classified according to physical characteristics like water temperature, depth and light available.
Thus, sarting from the surface towards the deep sea, we have the intertidal whose limits are defined by the oscillation of the tides along the coast.
The benthic division comprises the environment associated with the seabed while the pelagicdivision comprises the entire water column.
The pelagic domain is often divided into five zones associated with depth:
Epipelagic zone - till 200 m deep;Mesopelagic zone - between 200 and 1000 m deep;Bathypelagic zone - from 1000 to about 4000 m deep; Abyssopelagic zone - water above abyssal plains; Hadopelagic zone - portion of the water associates to the bottom of the ocean trenches with more than 6000 m deep.
In the ocean light penetrates only the surface layer. The area where there is sufficient light to take photosynthesis is called photic zone.
The depth of the photic zone depends on factors that interfere with the penetration of light into the water, ranging from values of around 5 m in areas of high turbidity and 200 m in clear waters.
The aphotic zone corresponds to the area of the ocean where there is no light.