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Transcript
The Vast World Ocean Ocean Floor Features Seafloor Sediments Resources from the Seafloor The Vast World Ocean The Blue Planet Nearly 71% of Earth’s surface is covered by the global ocean The oceans haven’t really been a huge focus of study until the late 1800’s As technology becomes better, it allows us to study what happens underneath the oceans Oceanography a science that draws on the methods and knowledge of geology, chemistry, physics, and biology to study all aspects of the world ocean Geography of the Oceans The world ocean can be divided into four main ocean basins Pacific Ocean the largest of the four oceans; it covers more than half of the ocean surface area on Earth Atlantic Ocean about half the size of the Pacific and not quite as deep Indian Ocean slightly smaller than the Atlantic; it is located almost entirely in the southern hemisphere Arctic Ocean about 7% the size of the Pacific; only one-quarter as deep as the other oceans Mapping the Ocean Floor The topography of the ocean floor is as diverse as that of the continents If the oceans were drained, we would find chains of volcanoes, tall mountain ranges, trenches, and large plateaus The more the oceans were studied, the more techniques were created to study the ocean floor Bathymetry (bathos = depth, metry = measurement) the measurement of ocean depths and the charting of the shape/topography of the ocean floor Current Technology Today’s technology allows scientists to study the ocean floor in a more efficient and precise manner than ever before Sonar (Sound Navigation and Ranging) using sound waves to determine depth and features on the ocean bottom Satellites Submersibles a small underwater craft used for deepsea research; allows for a human point of view under water for long periods of time Ocean Floor Features Oceanographers studying the ocean floor have divided it into three major regions Continental Margins Ocean Basin Floor Mid-Ocean Ridge Continental Margins Continental Margin the zone of transition between a continent and the adjacent ocean basin floor In the Atlantic Ocean, thick layers of undisturbed sediment cover the continental margin This region has very little volcanic or earthquake activity In the Pacific Ocean, oceanic crust is plunging beneath continental crust This force results in a narrow continental margin that experiences both volcanoes and earthquake activity Continental Shelf Continental Shelf the gently sloping submerged surface extending from the shoreline The average steepness of the shelf is equal to a drop of only about 2 meters per kilometer Continental shelves contain important mineral deposits, large reservoirs of oil and natural gas, and huge sand and gravel deposits Continental Slope Continental Slope marking the seaward edge of the continental shelf, this slope is steeper than the shelf and marks the boundary between continental crust and oceanic crust Submarine Canyons deep, steep-sided valleys cut into the continental slope Turbidity Currents occasional movements of dense, sediment-rich water down the continental slope Continental Rise Continental Rise in regions where trenches do not exist, the steep continental slope merges into this more gradual incline Steepness of the slope drops to about 6 m per km May be hundreds of km wide Ocean Basin Floor Ocean Basin Floor found between the continental margin and mid-ocean ridge Size of this region is almost 30% of Earth’s surface Region includes: Deep-ocean trenches Abyssal Plains Seamounts Guyots Deep-Ocean Trenches Deep-Ocean Trenches long, narrow creases in the ocean floor that form the deepest parts of the ocean Most are located along the margins of the Pacific Many exceed 10,000 meters in depth Challenger Deep in the Mariana Trench Trenches form at sites of plate convergence where one moving plate descends beneath another and plunges back into the mantle Abyssal Plains Abyssal Plains deep, extremely flat features; these regions are quite 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 the submerged volcanic peaks that dot the ocean floor They are volcanoes that have not reached the ocean surface Most found in the Pacific Ocean As volcanoes break the surface, they form islands The islands are eroded and eventually sink beneath the ocean level Guyots once active, now submerged, flat-topped structures Mid-Ocean Ridges Mid-Ocean Ridge found near the center of most ocean basins; an interconnected system of underwater mountains that have developed on newly formed ocean crust Longest topographic feature on Earth’s surface Exceeds 70,000 km in length Think of it like seams on a baseball Seafloor Spreading A high amount of volcanic activity takes place along the crest of the mid-ocean ridge Seafloor 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 zones where mineral-rich water, heated by the hot, newly-formed oceanic crust, escapes through cracks in ocean crust As the super-heated, mineral-rich water comes into contact with the surrounding cold water, minerals containing metals precipitate out and are deposited Seafloor Sediments Types of Seafloor Sediments Ocean-floor sediments can be classified according to their origin into three broad categories Terrigenous Sediments Biogenous Sediments Hydrogenous Sediments Terrigenous Sediment Terrigenous Sediment sediment that originates on land Consist primarily of mineral grains that were eroded from continental rocks and transported to the ocean Larger particles (gravel/sand) settle near shore Smaller particles (clay) are carried out to sea and can take years to settle to the bottom Biogenous Sediment Biogenous Sediment sediment that is biological in origin; consists of shells and skeletons of marine animals and algae Calcareous Ooze most common type of biogenous sediment; it is produced from the calcium carbonate shells of organisms Siliceous Ooze composed primarily of the shells of diatoms (single-celled algae) and radiolarians (singlecelled animals that have shells made out of silica Hydrogenous Sediment Hydrogenous Sediment consists of minerals that crystallize directly form ocean water through various chemical reactions Make up a very small portion of ocean sediments Most common types: Manganese Nodules Calcium Carbonates Evaporites Resources from the Seafloor Energy Resources Oil and natural gas are the main energy products currently being obtained from the ocean floor Gas Hydrates compact chemical structures made of water and natural gas Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean-floor sediments Other Resources Sand and Gravel Used for landfill, to fill in recreational beaches, and to make concrete Manganese Nodules Manganese Nodules hard lumps of manganese and other metals that precipitate around a smaller object Used in the creation of many metal alloys Evaporative Salts Table salt (halite), drying fabric, de-icing roads