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The Earth’s Oceans The Water Planet The Blue Planet The world is dominated by interconnected oceans. It just depends on your viewpoint. If we view the Earth from the viewpoint of space, we can see that most of the water is in the Southern Hemisphere. The Blue Planet Nearly 71% of the Earth’s surface is covered by the global ocean. How Big is the Ocean 1. 2. 3. 4. The ocean covers about 360 million square miles of the Earth’s surface. Oceanographers divide the oceans into four major ocean basins: The Pacific The Atlantic The Indian The Arctic The Pacific Ocean The Pacific Ocean is the largest ocean. It is the largest single geographic feature on the Earth. It comprises more than half of the world’s oceans. With an average depth of about 3,900 meters, it is the deepest ocean in the world as well. The Atlantic Ocean The Atlantic Ocean is about half the size of the Pacific Ocean. The Atlantic is slightly shallower than the Pacific. Both the Atlantic and Pacific Oceans are bounded on their eastern and western sides by continents. The Indian Ocean While the Indian Ocean is slightly smaller than the Atlantic, it is about the same depth. Unlike the Atlantic and Pacific, the Indian Ocean is located almost entirely in the southern hemisphere. The Arctic Ocean The Arctic Ocean accounts for only about 7% of the world’s oceans. It is also only about one fourth as deep as the other oceans of the world. The World’s Oceans • All the oceans are really one large body of water. • The average depth of the oceans is 3800m or 3.8km. • 97% of the water on Earth is found in the oceans (only 3% of the water in the world is freshwater). Bathymetry The study of the oceans topography is called bathymetry. Oceanographic History The first serious look at the ocean came in the 1870’s. The Challenger conducted an 6-year voyage to study the worlds oceans. The Challenger sailed approximately 128,000 miles on its journey. Current Technologies for Exploring the Ocean Today, there are various technologies available to explore the ocean. These include sonar, satellites and submersibles. This allows modern scientists to explore the ocean floor more efficiently and accurately than ever. Sonar Sonar stands for Sound Navigation and Ranging. Sound waves are bounced off the ocean bottom and timed as they arrive. The difference in arrival time can be translating into a depth. Sonar Today, modern multibeam sonar sends out multiple sound signals and receivers to establish the depth of wide bands along the ocean floor as opposed to narrow points. Side-scan Sonar • Side-scan sonar is used to create an image of large areas of the • • • sea floor. This tool is used for mapping the seabed for a wide variety of purposes, including creation of nautical charts and detection and identification of underwater objects and bathymetric features. Side scan uses a sonar device that emits fan-shaped pulses down toward the seafloor across a wide angle perpendicular to the path of the sensor through the water, which may be towed from a surface vessel or submarine, or mounted on the ship's hull. The intensity of the acoustic reflections from the seafloor of this fan-shaped beam is recorded in a series of cross-track slices. When stitched together along the direction of motion, these slices form an image of the sea bottom within the swath (coverage width) of the beam. The sound frequencies used in side-scan sonar usually range from 100 to 500 kHz; higher frequencies yield better resolution but less range. Side-scan Sonar Satellites Satellites are able to compensate for waves, tides, currents and atmospheric effects to produce ocean surface and topographic features images. Scientists have discovered that the ocean is not flat. Where seamounts and ridges occur the ocean bulges up. Where undersea canyons occur, the ocean has depressions. SEAsat Satellite Images Submersibles Submersibles are small underwater craft capable of diving to great depths. Submersibles such as Alvin and Sea Cliff II can reach ocean depths of between 4,000 and 6,000 meters, respectively. Submersibles More modern versions of submersibles are unmanned an operated with computers and joy sticks. These submersibles operate longer and cheaper because they have no crews that require life support or comforts. Autosub Ocean Topography The ocean floor has been divided into three major regions: 1. the continental margins 2. the ocean basin floor 3. the mid-ocean ridge The Continental Margins The continental margin includes the continental shelf, the continental slope and the continental rise. It does not include the abyssal plain. The Continental Margins: The Continental Shelf Continental shelves contain mineral deposits, oil reservoirs, natural gas, and huge sand and gravel deposits. The Continental Margins: The Continental Slope The continental slope is located just seaward of the continental shelf. Averaging only about 20 kilometers in width, it marks the boundary between the continental and oceanic crusts. The slope often has deep channels cut into them. These occur at time when the world’s oceans are low and rivers cut deeply into the exposed sediment. Sometimes large underwater landslides occur here that create “turbidity currents”. Turbidity Currents Artificially created turbidity current The Continental Margins: The Continental Rise • The continental rise marks the area of the ocean floor where the incline of the sea floor is reduced. The continental rise may be hundreds of kilometers wide. The Ocean Basin Floor Between the continental margin and the mid-ocean ridges, lies the ocean basin floor. Some of the features of the ocean floor basin include: deep-ocean trenches, abyssal plains and seamounts and guyots. Deep-ocean Trenches Deep-ocean trenches are long, narrow creases in the ocean floor that form in the deepest parts of the ocean. Most of the trenches form along the margins of the Pacific and exceed 10,000 meters in depth. The deepest know point on the planet is located in the Marianas Trench and is over 11,000 meters deep. These mark convergent plate boundaries. Abyssal Plains Abyssal plains are huge expanses of extremely flat sediments. They are possibly the flattest places on the planet. These plains are formed from sediment carried by turbidity currents and settling suspended sediments. Seamounts and Guyots Seamounts are undersea volcanic peaks that dot the ocean floor. They are volcanoes that have yet to reach the surface. Seamounts and Guyots Once volcanic islands break the ocean’s surface they begin to erode and form flattopped, once active structures called guyots. The Mid-Ocean Ridge Mid-Ocean ridges are found at the center of most ocean basins. It is an interconnected system of underwater mountains that develop above newly formed ocean crust. The Mid-Ocean Ridge Mid-Ocean ridges are areas of seafloor spreading or divergent plate boundaries that we talked about earlier. This is where new land is formed. Hydrothermal Vents • http://www.onr.navy. mil/focus/ocean/habit ats/vents1.htm Seafloor Sediments Ocean-floor sediments can be classified according to their origin into three broad categories: terrigenous (lithogenous) sediment, biogenous sediment, and hydrogenous sediment. Terrigenous Sediment • Terrigenous sediments consist primarily of mineral grains that were eroded from continental rocks and transported to the ocean. Seafloor Sediments Biogenous Sediment • Biogenous sediments consist of shells and skeletons of marine animals and algae. - Calcareous ooze is thick, common biogenous sediment produced by dissolving calcium carbonate shells. - Siliceous ooze is biogenous sediment composed of silica-based shells of single-celled animals and algae. Hydrogenous Sediment • Hydrogenous sediment consists of minerals that crystallize directly from ocean water through various chemical reactions. • One example is a manganese nodule. Biogenous Sediments Radiolaria Foraminifera Resources from the Seafloor Energy Resources Oil and natural gas are the main energy products currently being obtained from the ocean floor. Gas Hydrates • Gas hydrates are compact chemical structures made of water and natural gas. • Most oceanic gas hydrates are created when bacteria break down organic matter in oceanfloor sediments. Gas Hydrates Resources from the Seafloor Other major resources from the ocean floor include sand and gravel, evaporative salts, and manganese nodules. Sand and Gravel • The offshore sand-and-gravel industry is second in economic value only to the petroleum industry. Resources from the Seafloor Manganese Nodules • Manganese nodules are hard lumps of manganese and other metals (like cobalt, copper, and iron) that precipitate around a small object. Evaporative Salts • When seawater evaporates, the salt increases in concentration until it can no longer remain dissolved. When the concentration becomes high enough, the salts precipitate out of solution and form salt deposits. • The most economically important salt is halite— common table salt. Manganese Nodules