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Key Points 1. The ocean floor is mapped by bathymetry. 2. Ocean-floor topography varies with location. 3. Continental margins are “active” or “passive”.

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Presentation on theme: "Key Points 1. The ocean floor is mapped by bathymetry. 2. Ocean-floor topography varies with location. 3. Continental margins are “active” or “passive”."— Presentation transcript:

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 Posidonius conducted the first bathymetric studies conducted the first bathymetric studies 85 B.C. 85 B.C. 2 km Bathymetry = study of ocean floor contours The early, simplest methods involved lowering a weight on a line.

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

4 Reginald Fessenden ( ) Canadian inventor Canadian inventor in 1914, developed a type of sonar system for locating icebergs in 1914, developed a type of sonar system for locating icebergs “Iceberg Detector and Echo Depth Sounder”

5 Reginald Fessenden ( ) Canadian inventor Canadian inventor in 1914, developed a type of sonar system for locating icebergs in 1914, developed a type of sonar system for locating icebergs “Iceberg Detector and Echo Depth Sounder”

6 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.

7 During World War I ( ) used to detect enemy submarines used to detect enemy submarines Meteor expedition ( ) used to study the seabed used to study the seabed

8 World Ocean Floor

9 Pacific Ocean

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

13 Sea surface Seafloor

14 ? Seafloor

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

16 Mapped by: Geosat, TOPEX/Poseidon, and Jason-1 Seafloor topography inferred from sea surface height measurements

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

18 earthquakes volcanic activity Continental margins are “active” or “passive”. Pacific-Type Atlantic-type Pacific-Type Atlantic-type no earthquakes no 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) Average width: 1280 km (800 miles) Granitic rock covered by sediments Granitic rock covered by sediments Methane compounds Methane compounds

21 up to 350 km most material comes from erosion of continent

22 Atlantic

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

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

25 Bering Strait

26

27 Allowed human migration 12,000 years ago Bering Strait

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

31 m Monterey Bay canyon

32 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.

33

34 turbidity current an underwater “avalanche” of sediment Most geologists believe that submarine canyons have been formed by abrasive turbidity currents plunging down the canyons.

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

36 The topology of deep-ocean basins differs from that of the continental margin Deep-ocean basins comprise mainly: 1)oceanic ridge systems 2)sediment-covered plains

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

38 Mid-Atlantic Ridge

39 transform faults fracture zones

40 Hydrothermal vents are hot springs on active oceanic ridges 350 degrees Celsius 350 degrees Celsius discovered in 1977 by Robert Ballard and J. F. Grassle discovered in 1977 by Robert Ballard and J. F. Grassle Alvin

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

42

43 “black smokers” 20 m 350 o C 2,800 m depth solutions exiting vents are acidic (pH = ~3.5) and contain up to 300 ppm hydrogen sulfide (H 2 S) a highly reduced molecule, so much energy can be obtained when it is oxidized a highly reduced molecule, so much energy can be obtained when it is oxidized

44 hydrothermal vent community includes snails, shrimps, crabs, tube worms, fishes includes snails, shrimps, crabs, tube worms, fishes depends on chemosynthetic bacteria for food depends on chemosynthetic bacteria for food chemosynthesis Tube worms deep-sea vent mussels

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

46 Volcanic seamounts and guyots project above the seabed Volcanic seamounts and guyots project above the seabed about 30,000 about 10,000 in the Pacific >1 km in height >1 km in height important fishing areas important fishing areas Emperor Seamounts seamount

47 Guyot: flat-topped seamount that once reached the surface

48 Trench: arc-shaped depression on the deep-ocean floor occur near subduction zones occur near subduction zones deepest places in the ocean deepest places in the ocean most in the Pacific most in the Pacific

49 Peru-Chile trench Puerto Rico trench

50 Japan Trench 10,595 m Mariana Trench 11,022 m

51 Trieste reached the bottom of the Mariana Trench in 1960 – Challenger Deep reached the bottom of the Mariana Trench in 1960 – Challenger Deep

52 Kaiko Japanese deep-sea submarine Japanese deep-sea submarine sampled bacteria from the bottom (10,897 m) of the Mariana Trench in 1996 sampled bacteria from the bottom (10,897 m) of the Mariana Trench in 1996

53 Sampling of the world's deepest sea sediment by "Kaiko" at the Mariana Trench, Challenger Deep Bacteria collected from the Mariana Trench

54 Nereus

55 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.


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