The Ocean Basins The Water Planet q Nearly

The Ocean Basins

The Water Planet q Nearly 3/4 ths of the worlds surface lies beneath a body of water called the global ocean. q The global ocean contains more than 97% of all the water on Earth

Divisions of Global Ocean § Divided into 5 major oceans: Atlantic, Pacific, Indian, Arctic, and Southern. § Pacific is the largest and deepest ocean on Earth (West coast) § Atlantic is second largest ( East coast) • Indian is the 3 rd largest • Southern extends from coast of Antarctica to 60˚ • The Arctic ocean is the smallest ocean, and surrounds the north pole.

Ocean/ Sea • Sea is a body of water that is smaller than an ocean that may partially surrounded by land. They are usually located where land the ocean meet. Dead Sea

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

Tanner sounding machine • developed around 1880 Sigbee sounding machine • developed around 1880 http: //woodshole. er. usgs. gov/operations/sfmapping/images/theb 0914_small. jpg http: //www. nefsc. noaa. gov/history/ships/albatross 1/sigsbee-sounding. jpg Sometimes the weight was tipped with wax to retrieve a sample of bottom sediment.

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

Scientists now use beams of sound to measure depth. SONAR: Sound navigation and ranging Sound travels through water at about 1500 m/s. So if you measure the time it takes to leave and bounce off ocean floor and return you can calculate the depth. Titanic • sank on its maiden voyage in 1912

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”

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

During World War I (1914 -1918) • used to detect enemy submarines Meteor expedition (1925 -1927) • used to study the seabed http: //www. eastlanddisaster. org/uc 97. jpg http: //oceanworld. tamu. edu/resources/ocng_textbook/chapter 02/Images/Fig 2 -2 s. jpg

Heinrich Berann (1915 -1999) • 　Austrian artist

World Ocean Floor

Pacific Ocean http: //www. panorama-map. com/Europeans/Berann/berannpacificocean 500. html

Mt. Everest (1962) http: //www. berann. com/panorama/Everest. jpg

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

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

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

Sea surface Seafloor

Sea surface Seafloor ？

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

Geosat satellite

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

Ocean-floor topography varies with location

>50% of Earth’s surface is >3, 000 m below sea level

Oceans can be divided into two major provinces: 1) continental margin: shallow parts of ocean floor made of continental crust 2) ocean basin: deep part of ocean beyond continental margin.

Continental margins are “active” or “passive”. Near converging plates • earthquakes • volcanic activity Face the edges of diverging plates • no earthquakes • no volcanic activity

Three parts of Continental Margins: 1. Continental shelf: part of continent that is covered with water ( average depth is 60 m. ) 2. Continental slope: depth increases by several thousand meters 3. Continental rise: raised wedge at the base of c. slope that is formed by sediments

Continental shelf: shallow submerged extension of a continent

• up to 350 km • most material comes from erosion of continent http: //media. allrefer. com/s 1/l/c 0601400 -continental-shelf. jpg

Atlantic http: //www. cryingvoice. com/Evolution/gifs/hydro. NA. jpg

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

Continental shelves are greatly influenced by changes in sea level Sea level rise

Sea level is now high and rising as the ocean warms. Wisconsin glaciation http: //en. wikipedia. org/wiki/Image: Sea_level_temp_140 ky. gif

Wisconsin glaciation • 70, 000 to 10, 000 years ago Ice sheets • 3 -4 m thick • caused sea level to drop 125 m ice age http: //en. wikipedia. org/wiki/Image: Northern_icesheet_hg. png

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

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

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

Submarine canyons form at the junction between continental shelf and continental slope. Deep V shaped valleys often found at the mouths of major rivers.

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

Monterey Bay canyon 2000 m http: //www. marine-geo. org/gallery/images/Monterey. Bay 3 D. jpg

Suruga Bay

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

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/Turbidity. Current. jpg

Continental rises form as sediments accumulate at the base of the continental slope continental rise • much sediment • most of the sediment that forms the continental rise is transported to the area by turbidity currents

The topology of deep-ocean basins differs from that of the continental margin Deep-ocean basins comprise mainly: 1) Trenches- long narrow depressions. Form when one plate subducts below another plate 2) Oceanic ridge systems- underwater mountain ranges. Form where plates pull away from each other 3) Sediment-covered plains- vast, flat areas where the ocean is more than 4 km deep

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

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

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

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

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

Alvin • can carry 3 people • can dive to 4000 m • 1964 – 2007 • >4000 dives manned submersible Bathyscaph( free-moving) • 6, 500 m unmanned submersible Bathysphere ( remains connected) • 11, 000 m

“black smokers” 350 o. C 20 m 2, 800 m depth http: //www. csa. com/discoveryguides/vent/images/smoker. jpg http: //whyfiles. org/coolimages/csi/nur 04506. jpg solutions exiting vents are acidic (p. H = ~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

“black smokers” seawater is heated and reacts chemically with the surrounding basalt http: //www. divediscover. whoi. edu/images/vent_chemistry. jpg

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

Hydrothermal vents are common on oceanic ridges http: //www. nature. com/nature/journal/v 439/n 7079/images/hydro_vents/index. html AND in freshwater (Lake Baikal)

Abyssal plains and abyssal hills cover most of Earth’s surface. Flat Abyssal plains • 50% of the ocean floor • common in the Atlantic • rare in the Pacific • covered by fine sediment Abyssal hills • small sediment-covered extinct volcanos or rock

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

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

Trench: arc-shaped depression on the deep-ocean floor • occur near subduction zones • deepest places in the ocean • most in the Pacific • Deepest is Mariana Trench in Pacific >11, 000 m http: //geology. com/records/ocean-trench. gif

>8 km ( deepest in Atlantic Peru-Chile trench Puerto Rico trench Peru-Chile : longest trench 3, 650 miles or 5, 900 km http: //en. wikipedia. org/wiki/Image: Peru-Chile_trench. jpg

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

Trieste • reached the bottom of the Mariana Trench in 1960 ( manned)

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

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

• lost at sea in typhoon in 2003 • Cost 15 Million

Deep. Sea Challenger • On March 26, 2012, Canadian film director James Cameron piloted the craft to accomplish this goal, becoming the first person to reach Challenger Deep in a one-man craft

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.