Oceanography Exam #1

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Oceanography
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Study of the water of the oceans, the life in it, and the Earth beneath it.
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Four Sub-disciplines of Oceanography
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Geological, Chemical, Physical, Biological
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Ocean covers __% of Earth’s surface, and contains __% of Earth’s water.
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71, 97
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The ocean and its ____ ____ control ____ ____.
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Stored Heat, Global Climates
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The ocean is important for…
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…commerce, transportation and recreation.
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Ocean Resources
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Water, Food, Minerals, Energy, Space
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Human Habitation in Coastal Zone
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3.2 Billion People Worldwide, 80% of US Citizens, 8 out of 10 Largest Cities, 3,600 people move to coast each day.
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The Four Principal Oceans (+1)
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Pacific, Atlantic, Indian, Arctic, (+Southern/Antarctic)
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Average Ocean Depth
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~3,796 Meters
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Average Elevation of Land
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840 Meters
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Deepest Part of Ocean
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Mariana’s Trench at 11,022 Meters Deep.
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Highest Mountain
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Mount Everest at 8,850 Meters High.
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Total Maximum Relief on Earth
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19,872 Meters
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Early Period
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Up to ca 1400 CE (Includes Middle Ages); First Used as Food Source, Migration/Trade by Vikings, Phonecians, Chinese, and Micronesians; Later by Romans & Greeks for Political/Military Reasons
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Early Period Accomplishments
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First Maps, Magnetic Compass, Size/Shape of Earth, System of Latitudes, Tides
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Middle Period
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ca 1400-1800 CE (Age of Discovery); Exploration/Mapping by Western Man, Used for Trade/Colonialism/National Security, No Academic Study.
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Middle Period Names
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Henry the Navigator, DeGamma, Magellan, Drake, Cook, Henry Hudson, Columbus
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Middle Period Accomplishments
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Accurate Maps of Worlds & Oceans, Sextant, Chronometer, System of Longitude, Mercator Projection Maps, Notes on Local Biota.
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Modern Period
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ca 1800 CE to Present; Primary Motivation Still Economic and Political, Includes First Systematic Scientific Studies
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Modern Period Accomplishments
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1777: Ben Franklin’s Map of Gulf Stream; 1807: US Coast and Geodetic Study (NOAA); 1830: Voyage of the Beagle, Darwin; 1872: Voyage of the HMS Challenger (First Purely Scientific Oceanographic Study)
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Pacific Ocean
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Largest (width half circumference of Earth), nearly circular, deepest (greatest average depth because of many deep trenches), coldest and least salty, and numerous islands and volcano.
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Atlantic Ocean
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Second largest, “S” shaped, shallower (large central ridge, average depth 3310 m), saltier than average; Mediterranean water.
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Indian Ocean
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South of Tropic of Cancer, roughly symmetrical (more or less circular), smallest of the three main oceans.
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Arctic Ocean
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Almost enclosed by land, nearly all above the Arctic circle, dominated by ice, largest connection with Atlantic/major influence on Atlantic.
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Southern/Antarctic Ocean
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Defined by a set of physico‐chemical oceanographic parameters that distinguish the Antarctic water mass from the other water masses.
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Universe Origin
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13-15 Ga; Big Bang Theory
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Solar System Origin
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~5 Ga; Condensation of Solar Nebulae
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Earth Origin
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~4.5 Ga; several hypothesis; most involve condensation and collapse of part of the solar nebulae, era of impacts; then fractionation/ differentiation, degassing, cooling.
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Atmosphere Origin
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Ongoing; original atmosphere lost; atmosphere continually evolves as a result of degassing, abiotic and biotic processes; earliest known atmosphere much different from current.
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Oceans Origin
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About 4.0 Ga (Billion Years Ago)
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Oldest Fossils
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3.5 Ga (Billion Years Ago)
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Oldest Rocks on Earth
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3.99 Ga (Billion Years Ago)
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Oldest Ocean Floor
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200 Ma (Million Years Ago)
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Continental Margin
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Submarine Extensions of the Continents
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Deep Ocean Basins
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Deep ocean floor, fundamentally different from the continents.
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Mid-Ocean Ridge/Oceanic Ridge
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Submarine mountain range; MOR
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Continental Margin Features
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(From On Shore to Off Shore) Continental Shelf, Shelf Break, Continental Slope, Continental Rise
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Continental Shelf
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Extends from shoreline to shelf break, shallow/lowrelief/gently sloping (~1-2Âș), similar topography to adjacent coast, average width 70 km but up to 1,500 km, average depth of shelf break 135 m
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Continental Slope
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Steeply sloping area extending seaward from shelf break to deep ocean floor; average 4Âș slope; depth range ~200 m to ~3,000 m; submarine canyons cut into slope by turbidity currents (mixture of seawater and sediments, move under influence of gravity, erode canyons, deposit sediments at base of slope)
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Continental Rise
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Transition between continental margin and deep ocean; composed of aggregated sea fans; turbidite deposits (graded bedding, submarine fans); distal end of submarine fans become abyssal plains
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Features of Deep Ocean Basin
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Abyssal Plains, Volcanic Peaks, Ocean Trenches, Volcanic Arcs
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Abyssal Plains
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Flattest places on Earth (<1Âș), very deep (Average Depth: 4,500-6,000 m); depositional surfaces extending seaward from base of continental rise; sediment comes from suspension settling of very fine particles; sediments cover ocean crust irregularities.
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Volcanic Features
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Ocean crust that pokes through sediment cover; below sea level: seamounts, tablemounts or guyots at least 1.0 km above sea floor & abyssal hills or seaknulls less than 1.0km; above sea level: volcanic islands (Bermuda, Canary Isles, etc)
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Ocean Trenches
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Linear, narrow, steep-sided, V-shaped depressions in the sea floor; deepest parts of ocean (>6,000 m); Mariana Trench at 11,022 m; majority in Pacific Ocean; Atlantic has 2 & Indian has 1; associated with subduction zones.
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Volcanic Arcs
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Curved/arched chain of volcanic mountains; always on landward side of ocean trench; Island Arc-Chain of Islands (Japan, Phillipines) & Continental Arc-Volcanic Mountain Ranges (Andes, Cascades)
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Mid-Ocean Ridge
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Longest mountain range on Earth circling the globe like the lines on a baseball; mostly transverses the middle of ocean basins; on average 2.5 km above sea floor with highest peaks about 2 km below sea level; wholly volcanic with basaltic lava; contains a central down-dropped rift valley; aka East Pacific Rise in Pacific Ocean and Mid Atlantic Ridge in Atlantic Ocean.
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Oceanic Ridge
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Prominent rift valley; steep, rugged slopes; concave up
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Oceanic Rise
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Gentler, less rugged slopes; sides are convex up
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Features of Mid-ocean Ridge
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Central rift valley, faults and fissures; sea-mounts; pillow basalts; hydrothermal vents (deposits of metal sulfides, unusual life forms); fracture zones and transform faults
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Transform Faults & Fracture Zones
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Long linear zones of weakness, cracks; offset axes of mid-ocean ridges; TF ocean floor on either side moves in opposite directions; FZ extensions of transform faults (aseismic, doesn’t move, no earthquakes)
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Pillow Lava
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Forms when hot lava comes into contact with cold sea water and quickly cools; basalt composition
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Hydrothermal Vents
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Heated subsurface seawater migrates thru cracks in ocean crusts; Warm Water Vents 30ÂșC/86ÂșF but 350ÂșC; dissolved metals precipitate to form metal sulfide deposits; unusual biological communities (able to survive without sunlight, archaebacteria and bacteria oxidize hydrogen sulfide gas to provide food)
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Pacific Ocean Floor
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Many large trenches; many oceanic islands, seamounts, guyots; few, poorly developed abyssal plains; narrow shelves, no continental rises; many island arcs; East Pacific Rise; marginal seas
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Atlantic Ocean Floor
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Few oceanic islands, seamounts, guyots; large, central oceanic ridge; large, extensive abyssal plains; few trenches (Puerto Rico, Sandwhich); wide shelves, and extensive continental rises, Passive Margin; large marginal seas (Gulf of Mexico, Mediterranean, North, Caribbean)
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Indian Ocean Floor
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Marginal seas (Red Sea, Persian Gulf, Bay of Bengal); Mid Indian Ridge, symmetrical, Y shaped, one branch in Red Sea, others connect with MAR and EPR; large abyssal plains and submarine fans; java trench
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Arctic Ocean Floor
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Covered by ice & difficult to study; series of three oceanic ridges running N to S; relatively shallow
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Density
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Fundamental property of matter that is important in one way or another to almost all aspects of oceanography; D=m/v or gm/cc; inversely proportional to temperature; less dense floats
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Earth’s Internal Structure
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Determined by seismic waves, rock samples from deep drilling, rock samples from deep earth, bulk chemical analyses
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Crust
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5-60 km thick
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Oceanic Crust
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dark colored, basaltic composition, avg density 3.0 gm/cc; avg thickness 6 km
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Continental Crust
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light colored, granitic composition, avg density 2.7 gm/cc, avg thickness 35 km
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Mantle
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2900 km thick, Iron & Magnesium rich minerals, avg density 5.5 gm/cc, density of uppermost mantle 3.0-3.3 gm/cc
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Core
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3500 km thick, iron-nickel alloy, fluid/plastic outer core, solid/rigid inner core
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Lithosphere
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100 km thick, rigid/brittle/breaks under stress, all crust and small portion of upper mantle, avg density 2.9-3.0 gm/cc
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Asthenosphere
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600 km thick, plastic/ductile/bends or flows under stress but breaks when shocked; includes upper 1/4 of mantle; avg density 3.1-3.3 gm/cc
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Mesosphere
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2200 km thick; more or less rigid down to outer core
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Mohorovicic Discontinuity “MOHO”
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boundary between crust and mantle
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Isostasy
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A condition of flotational equilibrium among various units of the lithosphere “floating” in the asthenosphere, Application of Archimedes Principle to the lithosphere and asthenosphere, Less dense materials float higher than more dense materials.
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Relative Time
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