written by: Aggeliki K.
• edited by: Lamar Stonecypher
• updated: 4/5/2013
The study of the ocean floor topography is interesting since it offers details of a vast area comprised of hills, mountains, and valleys, all covered with water. The ocean floor topography starts with the Outer Continental Shelf followed by the Continental Slopes, and subsequently the Ocean Floor.
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What Is Ocean Floor Topography?
The term "topography" implies the study of numerous landforms that exist on or below the earth. Ocean floor topography refers to the different forms in which the ocean floor bottom can exist. You may perceive the ocean floor to be flat and sandy like the beach, but the truth is there are many different surfaces. As scientific knowledge has advanced, the capability to envisage these remote sites has increased significantly. Science has established that the topography of the ocean floor is similar to the ground topography with features such as valleys, mountains, and plateaus. Three quarters of the Earth consists of ocean water. All these details are incorporated on underwater topography maps.
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Continental Margin and Oceanic Divisions
Radical geological changes are observed at the boundary between the earth and the ocean. This intermediary region is called the Continental Margin. This zone consists of the Outer Continental Shelf followed by the Continental Slopes. The thick and heavy continental stonework is replaced by a thin basalt layer.
The Outer Continental Shelf starts as the water begins. This zone is shallow, slopes progressively, and normally holds water that is not very deep. The Continental Shelf width changes significantly depending on the locality, ranging from a few kilometers to hundreds of kilometers. As the Continental Shelf is crossed, the ocean floor descends steeply. These sharply sloping sections are known as the Continental Slopes. They identify the border between the granite of the continent, and the basaltic crust of the ocean.
Deep valleys have been observed in the Continental Slopes. It is believed that these valleys have been created due to the earthquakes, or have been eroded by violent ocean currents.
The divisions of the ocean water according to depth are known as Abyssal Zones. Each layer has its own characteristic features of pressure, temperature, salinity and biodiversity. The deepest oceanic zone is the hadalpelagic zone that lies between 6,000–11,000 meters.
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Mapping the Oceans with Radar Altimetry
Radar altimeters have been developed for mapping ocean floor topography, including the valleys and hills of the ocean surface. A microwave pulse is forwarded by these devices to the ocean surface, and time is measured for this signal to return. A microwave radiometer adjusts for any obstruction produced by the atmospheric water vapor. Other adjustments are also necessary because of the ionosphere electrons and the air in the atmosphere.
The shape and strength of the return signal presents information regarding the speed of wind, and the height of ocean waves. This data is utilized to determine the speed and direction of the oceanic currents. The variations in the global climate, and heat accumulated in the ocean are also measured.
Other ways to explore the seabed involve the use of small manned submarines, ROVs, and baited camera stations. However, the extreme pressure of these depths (almost 1,000 Atm in some depths), makes exploration a very difficult and costly task.
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The Extremes of Ocean Floor Life
Life on the ocean floor is extremely meager, as on an extensive desert. Marine organisms choose low waters, where the photosynthesis energy is rich, offering abundant food. The oceanic floor has numerous oases, including cold seeps, hydrothermal vents, and whale falls.
In the cold seeps, brine filled with methane escapes from the sea floor cracks, providing energy for bacteria. Minerals released from hydrothermal vents are also processed by bacteria. Organisms in these depths depend on sinking organic matter to feed that falls on the ocean floor in the form of marine snow. A whale fall is basically a whale that dies and sinks in the deep ocean. Since scavengers are limited on the floor of the ocean, several years may be required for the consumption of whales. A whale fall may occur as frequently in the deep ocean as one in every 20-25 kilometers of seabed.
Since light and food is so scarce, fish have developed large eyes, slow metabolisms, weak muscles and elongated bodies. Many of them are also hermaphroditic, since it is difficult to find a breeding mate in this vastness.