Earth / Environmental Science Ch. 14 THE OCEAN FLOOR The Blue Planet Nearly 70% of the Earth s surface is covered by the global ocean It was not until the 1800s that the ocean became an important focus of study. This is why Earth is often referred to the Blue Planet or also Water Planet Oceanography - The science that draws on the methods and knowledge of geology, chemistry, physics, and biology to study all aspects of the world s oceans. Geography of Oceans The world s oceans can be divided into four main ocean basins: the Pacific Ocean the Atlantic Ocean the Indian Ocean, and the Arctic Ocean Pacific - The largest ocean - covers more than half the surface area on Earth. It is also the deepest Ocean reaching an average depth of 3940 meters. Atlantic - Is approximately half the size of the Pacific, and not quite as deep. The Atlantic and Pacific are bounded to the east and west by continents. Indian - Although slightly smaller, the Indian Ocean has approximately the same depth of the Atlantic. It is located almost entirely in the southern hemisphere. Arctic Ocean - Is about 7% of the size of the Pacific Ocean. It is also a little more than one-quarter deep as the rest of the oceans
Mapping the Ocean floor The topography of the ocean floor is as diverse as that of the continents. Bathymetry - Is the measure of ocean depths and charting of the shape or topography of the ocean floor. Today s Technology - includes sonar, satellites, and submersibles. These allow scientists to study the ocean floor in a more efficient and precise manner than ever before Sonar Was invented in the 1920s. Sonar is an acronym for SOund NAvigation and Ranging Sonar works by transmitting sound waves toward the ocean bottom. Satellites Measure the ocean surface from space Mountains and ridges produce elevated areas on the ocean surface. Features such as canyons and trenches cause slight depressions. These rises and depressions are not visible by the human eye Satellites can measure variations in sea-surface height as small as 3 to 6 centimeters Submersibles Submersibles- Are small underwater crafts used for deep-sea research. These are used to collect information about areas of the ocean that are unreachable by humans. The first submersible used was in 1934 by William Beebe. Descending to a depth of 923 meters
Ocean Floor Features The ocean floor regions are the continental margins, the ocean basin floor, and the mid-ocean ridge Continental Margin Continental Margin - The zone of transition between a continent at the adjacent ocean basin floor Continental Shelf - the gently sloping submerged surface Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas and huge sand and gravel deposits. They also contain important fishing grounds, which are significant sources of food Continental Slope Is the seaward edge of the continental shelf. It is steeper than the shelf and marks the boundary between continental crust and oceanic crust Submarine canyons - Deep, steep-sided valleys that cut into the continental slope Turbidity currents - Occasional movements of dense, sediment-rich water down the continental slope Continental Rise Continental Rise - The steep continental slope that merges into a more gradual incline The continental rise may be hundreds of kilometers wide, when a continental slope averages around 20 kilometers Ocean Basin Floor Ocean basin floor- the area between the continental margin and the midocean ridge. Deep ocean trenches form at sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle
Abyssal Plains Deep, extremely flat features. Possibly the most level places on earth. The sediments that make up abyssal plains are carried there by turbidity currents or deposited as a result of suspended sediments settling. Seamounts and Guyots Seamounts- Submerged volcanic peaks that dot the ocean floor The majority of seamounts are found in the Pacific Ocean. They are mainly volcanoes that have not reached the surface Guyots - are once-active, now-submerged, flat-topped structures. Mid-Ocean ridges Is found near the center of most ocean basins This system is the longest topographic feature on the Earth s surface, exceeding 70,000 kilometers in length. Sea-floor spreading Occurs at divergent plate boundaries where two lithospheric plates are moving apart New ocean floor is formed at mid-ocean ridges as magma rises between the diverging plates and cools Hydrothermal vents Hydrothermal vents form along mid-ocean ridges. These are zones where mineral-rich water, heated by the hot, newly formed oceanic crust, escapes through cracks in the oceanic crust into surrounding water.
Types of Seafloor Sediments The ocean floor sediments can be classified according to their origin into three broad categories: Terrigenous sediments Biogenous sediments, and Hydrogenous sediments. Terrigenous Terrigenous sediment is sediment that originates on land. Terrigenous sediments consist of primarily mineral grains that were eroded from continental rocks and transported to the ocean. Biogenous Sediment Biogenous sediment is the sediment that is biological in origin Biogenous sediments consist of shells and skeletons of marine animals and algae. Calcareous ooze- Produced from the calcium carbonate shells of organisms. Hydrogenous Sediment Hydrogenous sediment consists of materials that crystallize directly from ocean water through various chemical reactions. These sediments make up an overall small portion of the ocean. Energy Resources Oil and natural gas are the main energy products currently being obtained from the ocean floor. Other energy sources are possible from the ocean and could be used in the future Oil and Natural Gas The ancient remains of microscopic organisms The percentage of world oil produced from offshore regions has increased from trace amounts in the 1930s to more than 30 percent today
Gas Hydrates Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean-floor sediments. Gas hydrates are compact chemical structures made of water and natural gas.