ES 106 2006 April 24 Oceanography I. Water planet A. 71% covered by sea B. All ‘oceans’ are interconnected C. Less land exposed in southern hemisphere II. Ocean basins—four main basins A. Pacific 1. ½ of all ocean surface 2. greater than area extent of all continents 3. average depth 3940 m 4. has deepest ocean trench in western portion—Mariana Trench B. Atlantic 1. ½ size of Pacific 2. Narrow—bounded by continents with similar shoreline shape 3. less average depth than Pacific C. Indian 1. depth nearly same as Atlantic 2. slightly smaller than Atlantic 3. bounded by land on north—mostly in southern hemisphere D. Arctic 1. small—7% of Pacific 2. shallow— ¼ average depth of other oceans E. Average elevation—Continents vs. Oceans 1. continents—840 m above sea level 2. oceans—3730 m below sea level: 4+ times elevation above sea level III. Ocean Floor A. Mapping 1. Challenger—127,500 km voyage in 1870s a. Depth—by weighted line b. Salinity, temperature, clarity 2. Modern depth measurements by SONAR a. SOund Navigation And Ranging b. Ping emitted is received c. Distance calculated by travel time of ping d. Sidescan instruments show details, not depth 3. Seismic Reflection Profiles a. Explosions produce sediment-penetrating sound waves b. Shows information about character of sea-floor 4. Satellilte Radar Altimiters a. Measure height of sea surface b. Gravity causes irregularities 1) Higher surface over undersea mountains 2) Lower surface over deep sea floor c. Ability to detect small scale differences B. Provinces of the sea floor1. continental margin a. continental shelf 1) part of continental crust flooded by ocean 2) narrow, gently sloping zones to about 130 m depth b. drops off at continental slope 1) very narrow 2) markedly steeper than shelf c. submarine canyons 1) cut outer shelf and slope 2) deliver sediment to ocean basin floor 2. ocean basin floor a. most is abyssal plains—flat, featureless surface b. deep ocean trenches—small portion at lithosphere plate convergence c. seamounts—volcanic peaks d. plateaus—volcanic plains 3. oceanic ridge a. tectonic feature of divergent lithospheric plates b. 1000 to 4000 km wide, 2000 to 3000 m high—not topographic marvel in appearance IV. Sea Floor Sediments A. Most of ocean floor covered by sediment B. Most of this sediment is fine mud C. Three broad groups of sea floor sediment types 1. terrigenous—from land sources 2. biogenous—from organisms 3. hydrogenous—precipitated straight from water D. Terrigenous 1. sand and gravel a. usually near shore b. can be carried to deep ocean via submarine canyons in a turbidity current 1) density flow of sediment and water 2) expansive once it reaches deep sea floor 3) unique bedding pattern: coarse-to-fine in a single bed 2. abyssal clay layer a. washed in by streams—takes decades to settle b. carried from continents by wind—settles on sea surface c. red or brown due to extensive time for oxidation of iron in it d. slow accumulation rates—1 cm / 50,000 years exists (extreme) E. Biogenous 1. shells and skeletons of marine organisms—plankton, etc. 2. mostly microscopic organisms near surface 3. calcareous ooze of algae and foram ‘tests’ a. coat bottom in areas shallower than 4500 mb. below 4500 m, completely dissolve due to elevated CO2 in deep sea water 4. siliceous ooze a. diatoms—algae b. radiolarians—animals 5. phosphate-rich material from bones, teeth, scales of larger animals F. hydrogenous 1. crystallize directly from sea water 2. can be diagnostic of environment, because they are not common 3. types a. manganese nodules—to 20 cm across, deep sea b. calcium carbonate precipitation—shallow warm seas c. metal sulfides—from undersea hot springs with high mineral content in water d. evaporites—if sea is restricted, and subject to high evaporation 1) halite—NaCl 2) anhydrite (CaSO4), gypsum (CaSO4.2H2O) G. Distribution of Sea floor sediments 1. coarse grained near continents 2. abyssal clay over wide expanses 3. biogenous sediments where there is high biologic productivity a. will predominate over other types of sediment b. calcareous where 4500+ m, siliceous in deeper areas 4. very little present in youngest area of ocean floor—ridge crest H. Climate change can be traced in sea floor sediment 1. biogenic productivity changes character in different climates 2. isotopes of various elements differ with differing temperatures V. Resources from the sea floor A. Energy resources 1. Gas and oil deposits on continental shelf a. Ancient marine organisms buried before decay b. Persian Gulf, Gulf of Mexico, California, North Sea, East Indies c. Deeper deposits not yet discovered 2. Methane Hydrate a. Mixture of water and methane, forms crystalline structure b. Low temperature or high pressure to create it 1) Permafrost 2) Deep continental shelf areas B. Other resources 1. sand and gravel— a. building material adjacent to urban areas b. rare areas contain metals or gems—diamond, garnet, tin, gold, platinum, titanium 2. salt evaporated from shoreline ponds—30% of world total salt use 3. manganese nodules—also contain iron, cobalt, copper,
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