Lecture6
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Lecture6
- 1. Lecture #6 Continental Margins and Ocean Basins 22 August 2007
- 2. The ocean floor is mapped by bathymetry http://www.the-planet-mars.com/spacecraft/Mars-global-surveyor.html Mars Global Surveyor Mars
- 8. Scientists now use beams of sound to measure depth.
- 9. Scientists now use beams of sound to measure depth.
- 15. V = speed of sound in water (about 1.5 km/sec) T = time Echo sounders sense the contour of the seafloor by beaming sound waves to the bottom and measuring the time required for the sound waves to bounce back to the ship.
- 20. Two new techniques improved studies of the seafloor: 1) multibeam echo sounders 2) satellite altimetry
- 23. Sea surface Seafloor
- 24. ？ Sea surface Seafloor
- 25. Gravitational attraction “pulls” water Over a 2000 m seamount, water rises about 2 m Seafloor Sea surface
- 26. Geosat satellite
- 27. http://www.ngdc.noaa.gov/mgg/image/global_grav_large.gif Mapped by: Geosat , TOPEX/Poseidon , and Jason-1 Seafloor topography inferred from sea surface height measurements
- 28. Ocean-floor topography varies with location
- 29. >50% of Earth’s surface is >3,000 m below sea level
- 30. Oceans can be divided into two major provinces: 1) continental margin 2) ocean basin
- 32. Three main parts of the continental margin:
- 33. Continental shelf: shallow submerged extension of a continent
- 36. active margin – often very narrow passive margin – broad The shelf width is usually determined by its proximity to a plate boundary.
- 37. Continental shelves are greatly influenced by changes in sea level Sea level rise
- 38. http://en.wikipedia.org/wiki/Image:Sea_level_temp_140ky.gif Sea level is now high and rising as the ocean warms. Wisconsin glaciation
- 42. http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif Allowed human migration 12,000 years ago Bering Strait
- 43. http://www.morien-institute.org/images/korea_2_sing.jpg Ice age sea level in Asia
- 44. http://cocos.arecaceae.com/indo19.gif Ice age sea level in Asia
- 45. Continental slopes connect continental shelves to the deep-ocean floor shelf break
- 46. Submarine canyons form at the junction between continental shelf and continental slope.
- 48. http://www.marine-geo.org/gallery/images/MontereyBay3D.jpg 2000 m Monterey Bay canyon
- 49. Suruga Bay
- 50. How do submarine canyons form? Submarine canyons cut into the continental shelf and slope, often terminating on the deep-sea floor in a fan-shaped wedge of sediment.
- 51. Submarine cables near Nova Scotia, Canada http://www.geol.lsu.edu/Faculty/Juan/PhysicalGeology_F2004/images/Turbidity2.gif
- 53. turbidity current an underwater “avalanche” of sediment http://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpg Most geologists believe that submarine canyons have been formed by abrasive turbidity currents plunging down the canyons.
- 58. Iceland fracture 15 cm/year http://library.thinkquest.org/C003124/images/diverg.jpg
- 60. http://www.berann.com/panorama/archive/image/PN_W_10.jpg Mid-Atlantic Ridge transform faults fracture zones
- 64. http://www.divediscover.whoi.edu/images/vent_chemistry.jpg “ black smokers” seawater is heated and reacts chemically with the surrounding basalt
- 66. Hydrothermal vents are common on oceanic ridges http://www.nature.com/nature/journal/v439/n7079/images/hydro_vents/index.html AND in freshwater (Lake Baikal)
- 69. blobfish orange roughy southern spineback southern whiptail
- 70. Guyot : f lat-topped seamount that once reached the surface http://en.wikipedia.org/wiki/Image:Guyot.jpg
- 72. Peru-Chile trench http://en.wikipedia.org/wiki/Image:Peru-Chile_trench.jpg Puerto Rico trench
- 73. Japan Trench 10,595 m Mariana Trench 11,022 m
- 76. Sampling of the world's deepest sea sediment by " Kaiko " at the Mariana Trench, Challenger Deep Bacteria collected from the Mariana Trench
- 78. Key Points 1. The ocean floor is mapped by bathymetry . 2. Ocean-floor topography varies with location . 3. Continental margins are “active” or “passive”. 4. The topology of deep-ocean basins differs from that of the continental margin.