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