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Key Points

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 topography of deep-ocean basins differs from that of the continental margin. Bathymetry = study of ocean floor contours.

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Key Points

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  1. 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 topography of deep-ocean basins differs from that of the continental margin.

  2. Bathymetry = study of ocean floor contours The early, simplest methods involved lowering a weight on a line. 2 km http://www-groups.mcs.st-and.ac.uk/history/BigPictures/Posidonius.jpeg • Posidonius • conducted the first bathymetric studies • 85 B.C.

  3. HMS Challenger • (1872-1876) • made the first systematic attempt to chart the basins of the world ocean • made 492 bottom soundings confirmed the discovery of the Mid-Atlantic Ridge

  4. Reginald Fessenden (1866-1932) • Canadian inventor • in 1914, developed a type of sonar system for locating icebergs http://en.wikipedia.org/wiki/Reginald_Fessenden “Iceberg Detector and Echo Depth Sounder”

  5. Reginald Fessenden (1866-1932) • Canadian inventor • in 1914, developed a type of sonar system for locating icebergs http://en.wikipedia.org/wiki/Reginald_Fessenden “Iceberg Detector and Echo Depth Sounder”

  6. 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. V = speed of sound in water (about 1.5 km/sec) T = time

  7. During World War I (1914-1918) • used to detect enemy submarines • Meteor expedition (1925-1927) • used to study the seabed http://www.eastlanddisaster.org/uc97.jpg http://oceanworld.tamu.edu/resources/ocng_textbook/chapter02/Images/Fig2-2s.jpg

  8. World Ocean Floor

  9. Pacific Ocean http://www.panorama-map.com/Europeans/Berann/berannpacificocean500.html

  10. Two new techniques improved studies of the seafloor: 1) multibeam echo sounders 2) satellite altimetry

  11. Multibeam systems combine many echo sounders. • up to 121 beams • signal sent every 10 secs <200 research vessels are equipped with multibeam systems

  12.  Seabed contours can be mapped using satellites. • Satellites cannot measure ocean depths directly • but, they can measure sea surface height

  13. Sea surface Seafloor

  14. ？ Sea surface Seafloor

  15. Sea surface Gravitational attraction “pulls” water Over a 2000 m seamount, water rises about 2 m Seafloor

  16. Seafloor topography inferred from sea surface height measurements http://www.ngdc.noaa.gov/mgg/image/global_grav_large.gif Mapped by: Geosat, TOPEX/Poseidon, and Jason-1

  17. Oceans can be divided into two major provinces: 1) continental margin 2) ocean basin (deep ocean floor – Basalt)

  18. Continental margins are “active” or “passive”. Pacific-TypeAtlantic-type • no earthquakes • no volcanic activity • earthquakes • volcanic activity

  19. Three main parts of the continental margin: 1. Shelf 2. Slope 3. Rise

  20. Continental shelf: shallow submerged extension of a continent • Average width: 1280 km (800 miles) • Granitic rock covered by sediments • Methane compounds

  21. up to 350 km • most material comes from erosion of continent http://media.allrefer.com/s1/l/c0601400-continental-shelf.jpg

  22. Atlantic http://www.cryingvoice.com/Evolution/gifs/hydroNA.jpg

  23. The shelf width is usually determined by its proximity to a plate boundary. active margin – often very narrow passive margin – broad

  24. Continental shelves are greatly influenced by changes in sea level (Ice Ages) Sea level rise

  25. Bering Strait http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif

  26. Bering Strait http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif

  27. Allowed human migration 12,000 years ago Bering Strait http://whyfiles.org/shorties/202mass_extinct/images/land_bridge.gif

  28. Continental slopes connect continental shelves to the deep-ocean floor shelf break

  29. Submarine canyons form at the junction between continental shelf and continental slope.(Edge of ocean basins)

  30. Monterey Bay canyon http://www.tahoemaps.com/files/Monterey_large.jpg

  31. Monterey Bay canyon 2000 m http://www.marine-geo.org/gallery/images/MontereyBay3D.jpg

  32. Submarine canyons cut into the continental shelf and slope, often terminating on the deep-sea floor in a fan-shaped wedge of sediment. How do submarine canyons form?

  33. turbidity current an underwater “avalanche” of sediment Most geologists believe that submarine canyons have been formed by abrasive turbidity currents plunging down the canyons. http://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpg

  34. Continental rises form as sediments accumulate at the base of the continental slope continental rise • much sediment • usually along passive margins

  35. The topology of deep-ocean basins differs from that of the continental margin • Deep-ocean basins comprise mainly: • oceanic ridge systems • sediment-covered plains

  36. Oceanic ridges circle the world • underwater mountain ranges • stretch 65,000 km • often covered with little sediment

  37. Mid-Atlantic Ridge http://www.berann.com/panorama/archive/image/PN_W_10.jpg

  38. Mid-Atlantic Ridge fracture zones transform faults http://www.berann.com/panorama/archive/image/PN_W_10.jpg

  39. Hydrothermal vents are hot springs on active oceanic ridges • 350 degrees Celsius • discovered in 1977 by Robert Ballard and J. F. Grassle Alvin http://www.mbari.org/molecular/images/EPR%20mussel-map.jpg

  40. Alvin • manned submersible • 6,500 m • can carry 3 people • can dive to 4000 m • 1964 – 2007 • >4000 dives • unmanned submersible • 11,000 m

  41. “black smokers” 350oC 20 m 2,800 m depth http://whyfiles.org/coolimages/images/csi/nur04506.jpg http://www.csa.com/discoveryguides/vent/images/smoker.jpg • solutions exiting vents are acidic (pH = ~3.5) and contain up to 300 ppm hydrogen sulfide (H2S) • a highly reduced molecule, so much energy can be obtained when it is oxidized

  42. hydrothermal vent community deep-sea vent mussels • includes snails, shrimps, crabs, tube worms, fishes • depends on chemosynthetic bacteria for food http://www.sciencedaily.com/images/2005/02/050223124700.jpg chemosynthesis Tube worms

  43. Abyssal plains and abyssal hills cover most of Earth’s surface. Flat • Abyssal plains • 40% of the ocean floor • common in the Atlantic • rare in the Pacific • covered by sediment • cold • Abyssal hills • small sediment-covered extinct volcanoes or rock • > 200 m (650 ft)

  44.  Volcanic seamounts and guyots project above the seabed • >1 km in height • important fishing areas seamount • about 30,000 • about 10,000 in the Pacific Emperor Seamounts http://upload.wikimedia.org/wikipedia/en/thumb/2/25/Seamount_Locations.png/350px-Seamount_Locations.png

  45. Guyot: flat-topped seamount that once reached the surface http://en.wikipedia.org/wiki/Image:Guyot.jpg

  46. Trench: arc-shaped depression on the deep-ocean floor • occur near subduction zones • deepest places in the ocean • most in the Pacific http://geology.com/records/ocean-trench.gif

  47. Peru-Chile trench Puerto Rico trench http://en.wikipedia.org/wiki/Image:Peru-Chile_trench.jpg

  48. Japan Trench 10,595 m Mariana Trench 11,022 m

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