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Transcript
Ocean Waters and the Ocean Floor The Vast World Oceans • 81% of the Southern Hemisphere is covered by oceans • 61% of the Northern Hemisphere is covered by oceans • 71% of the Earth is covered by oceans and marginal seas The Vast World Oceans • Three major oceans – Pacific (by far the largest) – Atlantic – Indian Composition of Seawater • 3.5% dissolved minerals in seawater • Salinity—the proportion of dissolved salts to pure water – Open ocean—33% to 37% salinity – Persian Gulf and Red Sea—exceeds 42% – Baltic Sea—below 10% Resources from Seawater • Salt (evaporating ponds) • Magnesium • Bromine—used for gasoline additives & fireproofing materials • Freshwater— desalination The Ocean’s Layered Structure • Based on temperature and salinity • Surface mixed zone—2% – Thickness depends on latitude and season • Thermocline (Transition zone)—18% – Drastic drop in temperature in nonpolar regions • Deep zone—80% – Around 4°C The Ocean’s Layered Structure • Salinity – Below the surface zone, salinity decreases rapidly – Halocline—corresponds closely with the thermocline Earth Beneath the Sea • Mountains, deep canyons and flat plains • Depth mapped by H.M.S. Challenger in the late 1800s. • Echo sounder (sonar) invented in the 1920s. • Three major units of topography – Continental margins – Ocean basin floor – Mid-ocean ridges Continental Margins • Zones – Continental shelf – Continental slope – Continental rise • Deep-sea fan – Muddy currents deposit sediment on the flat ocean floor Submarine Canyons and Turbidity Currents • Created by a process that operates far below the ocean surface such as: • Turbidity currents— downslope movements of dense, sediment-laden water, eroding the sea floor as they move The Ocean Basin Floor • Deep ocean trenches – Challenger Deep is more than 11,000 m (36,000 ft.) below sea level • Abyssal plains – Flat regions consisting primarily of sediments transported by turbidity currents • Seamounts – Volcanic mountains – Guyots • Submerged, flat-topped seamounts Mid-Ocean Ridges • Sites of seafloor spreading • Elevated position, faulting, and volcanic structures • Rift zone—where magma moves upward to create new slivers of oceanic crust Coral Reefs and Atolls • Coral reefs— constructed from skeletal remains and secretions of corals and algae, built up over thousands of years Coral Reefs and Atolls • Atolls—coral islands consisting of a continuous or broken ring of coral reef surrounding a central lagoon Seafloor Sediments • Terrigenous sediment – Consists primarily of mineral grains that were weathered from continental rocks • Biogenous sediment – Shells and skeletons of marine animals and plants (mainly microscopic) • Hydrogenous sediment – Minerals that crystallize directly from seawater through chemical reactions