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Transcript
THE OCEAN FLOOR 1. Oceanography – the study of the world’s oceans Nearly 71% of the earth’s surface is covered by oceans The world’s oceans: • Pacific- the largest and deepest • Atlantic – half the size of Pacific • Indian – almost entirely in Southern hemisphere • Arctic – smallest and shallowest 2. Mapping the Ocean Floor • Bathymetry-the measurement of ocean depths and the charting of the shape or topography of the ocean floor • Sonar – sound waves are transmitted toward the ocean floor and the time of echo reflections are measured • Satellites – the ocean surface is not flat • Submersibles 3. Ocean Floor Features Continental Margins • Continental Shelf – the gently sloping submerged surface extending from the shoreline, location of important mineral deposits, oil and gas, and huge sand and gravel deposits • Continental Slope – steeper, marks the boundary between continental crust and oceanic crust Submarine canyons – cut into continental slope, deep sided valleys, eroded by turbidity currents Turbidity currents are occasional movements of dense, sediment rich water down the continental slope • Continental rise – gently sloping Ocean Basin Floor • Deep ocean trenches – formed by subduction, deepest known place on Earth is the Challenger Deep of the Mariana Trench, 11,022 meters deep • Abyssal plains – extremely flat, most level places • Seamounts – submerged volcanic peaks • Guyots – once active, now submerged, flat topped remnants of volcanoes • Mid-Ocean Ridges – found near the center of most ocean basins • Sea-floor spreading – occurs at divergent plate boundaries, new crust is being formed • Hydrothermal vents – form along mid-ocean ridges, mineral-rich hot water comes in contact with cold water and metals are deposited 4. Seafloor Sediments • Terrigenous sediment – mineral grains eroded from continental rocks and transported to the ocean, large particles of sand and gravel deposited near shore, fine particles take years to settle • Biogenous sediment – consist of shells and skeletons on marine animals and algae Calcereous ooze – produced by calcium carbonate shells of organisms Siliceous ooze – produced by the shells of diatoms (shells made of silica) • Hydrogenous sediment – consists of minerals that crystallize directly from ocean water Manganese nodules Calcium carbonate (limestone) Evaporites 5. Resources From the Ocean Floor • Oil and Natural Gas – more than 30% of our oil and natural gas supplies are from offshore reserves • Gas hydrates – created when bacteria break down organic matter trapped in ocean floor sediments • Sand and gravel • Manganese nodules • Evaporative salts – when seawater evaporates, the salts precipitate out of solution, the most economically important is halite