lecture6
TRANSCRIPT
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Lecture #6Lecture #6
Continental Margins Continental Margins and Ocean Basinsand Ocean Basins
22 August 200722 August 2007
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The ocean floor is mapped by bathymetryThe ocean floor is mapped by bathymetry
http://www.the-planet-mars.com/spacecraft/Mars-global-surveyor.htmlhttp://www.the-planet-mars.com/spacecraft/Mars-global-surveyor.html
Mars Global SurveyorMars Global Surveyor MarsMars
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http://www.the-planet-mars.com/map-of-http://www.the-planet-mars.com/map-of-mars.htmlmars.html
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• no oceansno oceans• few storms few storms
MarsMars
http://www.modern.tsukuba.ac.jp/earth.jpghttp://www.modern.tsukuba.ac.jp/earth.jpg
EarthEarth
• oceans and clouds cover oceans and clouds cover 75% of the surface75% of the surface
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Posidonius Posidonius • conducted the first bathymetric studiesconducted the first bathymetric studies• 85 B.C.85 B.C.
http://www-groups.mcs.st-and.ac.uk/history/BigPictures/Posidonius.jpeghttp://www-groups.mcs.st-and.ac.uk/history/BigPictures/Posidonius.jpeg
2 km2 km
Bathymetry Bathymetry = study of ocean floor contours= study of ocean floor contours
The early, simplest The early, simplest methods involved methods involved lowering a weight lowering a weight on a line.on a line.
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http://www.nefsc.noaa.gov/history/ships/albatross1/sigsbee-sounding.jpghttp://www.nefsc.noaa.gov/history/ships/albatross1/sigsbee-sounding.jpg
Sigbee sounding machineSigbee sounding machine• developed around 1880developed around 1880
Tanner sounding machineTanner sounding machine • developed around 1880developed around 1880
http://woodshole.er.usgs.gov/operations/sfmapping/images/theb0914_small.jpghttp://woodshole.er.usgs.gov/operations/sfmapping/images/theb0914_small.jpg
Sometimes the weight was tipped with wax to Sometimes the weight was tipped with wax to
retrieve a sample of bottom sediment.retrieve a sample of bottom sediment.
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HMS HMS ChallengerChallenger
(1872-1876)(1872-1876)
• made the first made the first systematic attempt to systematic attempt to chart the basins of the chart the basins of the world oceanworld ocean
• made 492 bottom made 492 bottom
soundingssoundings confirmed the discovery of the Mid-Atlantic Ridge
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Scientists now use beams of sound to measure depth.Scientists now use beams of sound to measure depth.
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Scientists now use beams of sound to measure depth.Scientists now use beams of sound to measure depth.
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Scientists now use beams of sound to measure depth.Scientists now use beams of sound to measure depth.
TitanicTitanic• sank on its maiden voyage in 1912sank on its maiden voyage in 1912
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http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Reginald_FessendenReginald_Fessenden
Reginald Fessenden Reginald Fessenden (1866-1932)(1866-1932)• Canadian inventorCanadian inventor
• in 1914, developed a in 1914, developed a type of sonar system for type of sonar system for locating icebergslocating icebergs
““Iceberg Detector and Echo Depth Sounder”Iceberg Detector and Echo Depth Sounder”
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http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Reginald_FessendenReginald_Fessenden
Reginald Fessenden Reginald Fessenden (1866-1932)(1866-1932)• Canadian inventorCanadian inventor
• in 1914, developed a in 1914, developed a type of sonar system for type of sonar system for locating icebergslocating icebergs
““Iceberg Detector and Echo Depth Sounder”Iceberg Detector and Echo Depth Sounder”
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http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Reginald_FessendenReginald_Fessenden
Reginald Fessenden Reginald Fessenden (1866-1932)(1866-1932)• Canadian inventorCanadian inventor
• in 1914, developed a in 1914, developed a type of sonar system for type of sonar system for locating icebergslocating icebergs
““Iceberg Detector and Echo Depth Sounder”Iceberg Detector and Echo Depth Sounder”
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http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Reginald_FessendenReginald_Fessenden
Reginald Fessenden Reginald Fessenden (1866-1932)(1866-1932)• Canadian inventorCanadian inventor
• in 1914, developed a in 1914, developed a type of sonar system for type of sonar system for locating icebergslocating icebergs
““Iceberg Detector and Echo Depth Sounder”Iceberg Detector and Echo Depth Sounder”
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V = speed of sound in water(about 1.5 km/sec)T = time
Echo sounders Echo sounders
sense the contour sense the contour
of the seafloor by of the seafloor by
beaming sound beaming sound
waves to the waves to the
bottom and bottom and
measuring the measuring the
time required for time required for
the sound waves the sound waves
to bounce back to to bounce back to
the ship.the ship.
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During During World War IWorld War I (1914-1918) (1914-1918)
• used to detect enemy used to detect enemy submarinessubmarines
http://www.eastlanddisaster.org/uc97.jpghttp://www.eastlanddisaster.org/uc97.jpg
Meteor Meteor expedition (1925-1927)expedition (1925-1927)
• used to study the seabedused to study the seabed
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter02/Images/Fig2-2s.jpghttp://oceanworld.tamu.edu/resources/ocng_textbook/chapter02/Images/Fig2-2s.jpg
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World Ocean FloorWorld Ocean Floor
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http://www.panorama-map.com/Europeans/Berann/berannpacificocean500.htmlhttp://www.panorama-map.com/Europeans/Berann/berannpacificocean500.html
Pacific OceanPacific Ocean
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http://www.berann.com/panorama/Everest.jpghttp://www.berann.com/panorama/Everest.jpg
Mt. Everest Mt. Everest (1962)(1962)
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Two new techniques improved studies Two new techniques improved studies of the seafloor:of the seafloor:
1) multibeam echo sounders 1) multibeam echo sounders
2) satellite altimetry 2) satellite altimetry
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Multibeam systems combine many echo sounders.Multibeam systems combine many echo sounders.
• up to 121 beams• signal sent every 10 secs <200 research vessels are <200 research vessels are
equipped with multibeam equipped with multibeam systemssystems
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Seabed contours can be mapped using Seabed contours can be mapped using satellitessatellites..
Satellites cannot Satellites cannot measure ocean measure ocean depths directlydepths directly
• but, they can but, they can measure measure sea surface sea surface height height
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Sea surface
SeafloorSeafloor
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??Sea surface
SeafloorSeafloor
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Gravitational attraction “pulls” waterGravitational attraction “pulls” water
Over a 2000 m seamount, water rises about 2 mOver a 2000 m seamount, water rises about 2 m
SeafloorSeafloor
Sea surface
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Geosat satelliteGeosat satellite
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http://www.ngdc.noaa.gov/mgg/image/global_grav_large.gifhttp://www.ngdc.noaa.gov/mgg/image/global_grav_large.gif
Mapped by: Mapped by: GeosatGeosat, , TOPEX/PoseidonTOPEX/Poseidon, and , and Jason-1Jason-1
Seafloor topography inferred from sea surface Seafloor topography inferred from sea surface height measurementsheight measurements
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Ocean-floor topography varies with locationOcean-floor topography varies with location
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>50% of Earth’s >50% of Earth’s surface is >3,000 m surface is >3,000 m below sea levelbelow sea level
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Oceans can be divided into two major provinces: Oceans can be divided into two major provinces: 1) 1) continental margincontinental margin2) 2) ocean basinocean basin
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• earthquakes• volcanic activity
Continental margins are “Continental margins are “activeactive” or “” or “passivepassive”.”.
• no earthquakes• no volcanic activity
Face the edges of Face the edges of
diverging platesdiverging plates
Near converging Near converging
platesplates
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Three main parts of the continental margin:Three main parts of the continental margin:
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Continental shelfContinental shelf: : shallow submerged extension of a continent shallow submerged extension of a continent
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http://media.allrefer.com/s1/l/c0601400-continental-shelf.jpghttp://media.allrefer.com/s1/l/c0601400-continental-shelf.jpg
• up to 350 km
• most material comes from erosion of continent
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AtlanticAtlantic
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active margin – active margin – often very narrowoften very narrow
passive margin – passive margin – broadbroad
The shelf width is usually determined by its The shelf width is usually determined by its proximity to a plate boundary. proximity to a plate boundary.
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Continental shelves are greatly influenced by Continental shelves are greatly influenced by changes in sea levelchanges in sea level
Sea level riseSea level rise
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http://en.wikipedia.org/wiki/Image:Sea_level_temp_140ky.gifhttp://en.wikipedia.org/wiki/Image:Sea_level_temp_140ky.gif
Sea level is now high and rising as the ocean warms.
Wisconsin glaciationWisconsin glaciation
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ice ageice agehttp://en.wikipedia.org/wiki/Image:Northern_icesheet_hg.pnghttp://en.wikipedia.org/wiki/Image:Northern_icesheet_hg.png
Wisconsin glaciationWisconsin glaciation• 70,000 to 10,000 years ago70,000 to 10,000 years ago
Ice sheetsIce sheets• 3-4 m thick3-4 m thick• caused sea caused sea level to drop level to drop 125 m125 m
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Bering StraitBering Strait
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Bering StraitBering Strait
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Allowed human migration 12,000 years ago
Bering StraitBering Strait
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http://www.morien-institute.org/images/korea_2_sing.jpghttp://www.morien-institute.org/images/korea_2_sing.jpg
Ice age sea level in AsiaIce age sea level in Asia
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Ice age sea level in AsiaIce age sea level in Asia
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Continental slopes connect continental shelves to the Continental slopes connect continental shelves to the deep-ocean floordeep-ocean floor
shelf break
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Submarine canyons form at the junction between continental Submarine canyons form at the junction between continental shelf and continental slope.shelf and continental slope.
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http://www.tahoemaps.com/files/Monterey_large.jpghttp://www.tahoemaps.com/files/Monterey_large.jpg
Monterey Bay canyonMonterey Bay canyon
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http://www.marine-geo.org/gallery/images/MontereyBay3D.jpghttp://www.marine-geo.org/gallery/images/MontereyBay3D.jpg
2000 m2000 m
Monterey Bay canyonMonterey Bay canyon
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Suruga BaySuruga Bay
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How do submarine canyons form?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.
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Submarine cables near Nova Scotia, CanadaSubmarine cables near Nova Scotia, Canada
http://www.geol.lsu.edu/Faculty/Juan/PhysicalGeology_F2004/images/Turbidity2.gifhttp://www.geol.lsu.edu/Faculty/Juan/PhysicalGeology_F2004/images/Turbidity2.gif
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turbidity currentturbidity current
an underwater an underwater “avalanche” of sediment“avalanche” of sediment
http://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpghttp://unit.aist.go.jp/igg/rg/igi-rg/beta/sl-support/R-formation/TurbidityCurrent.jpg
Most geologists believe that submarine Most geologists believe that submarine canyons have been formed by abrasive canyons have been formed by abrasive turbidity currents plunging down the canyons.turbidity currents plunging down the canyons.
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Continental rises form as sediments accumulate at the base of the Continental rises form as sediments accumulate at the base of the
continental slopecontinental slope
continental rise
• much sedimentmuch sediment
• most of the most of the sediment that forms sediment that forms the continental rise the continental rise is transported to the is transported to the area by turbidity area by turbidity currentscurrents
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The topology of deep-ocean basins differs The topology of deep-ocean basins differs from that of the continental marginfrom that of the continental margin
Deep-ocean basins comprise mainly:Deep-ocean basins comprise mainly:
1)1) oceanic ridge systemsoceanic ridge systems
2)2) sediment-covered plainssediment-covered plains
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Oceanic ridges circle the worldOceanic ridges circle the world
• underwater mountain rangesunderwater mountain ranges• stretch 65,000 kmstretch 65,000 km• often covered with little sedimentoften covered with little sediment
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http://www.berann.com/panorama/archive/image/http://www.berann.com/panorama/archive/image/PN_W_10.jpgPN_W_10.jpg
Mid-Atlantic RidgeMid-Atlantic Ridge
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IcelandIceland
fracturefracture
15 cm/year15 cm/yearhttp://library.thinkquest.org/C003124/images/diverg.jpghttp://library.thinkquest.org/C003124/images/diverg.jpg
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http://www.berann.com/panorama/archive/image/http://www.berann.com/panorama/archive/image/PN_W_10.jpgPN_W_10.jpg
Mid-Atlantic RidgeMid-Atlantic Ridge
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http://www.berann.com/panorama/archive/image/http://www.berann.com/panorama/archive/image/PN_W_10.jpgPN_W_10.jpg
Mid-Atlantic RidgeMid-Atlantic Ridge
transform faultstransform faultsfracture zonesfracture zones
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Hydrothermal vents are hot springs on Hydrothermal vents are hot springs on active oceanic ridgesactive oceanic ridges
• discovered in 1977 by Robert Ballard and J. F. Grasslediscovered in 1977 by Robert Ballard and J. F. Grassle
AlvinAlvin
http://www.mbari.org/molecular/images/EPR%20mussel-map.jpg
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AlvinAlvin• can carry 3 peoplecan carry 3 people• can dive to 4000 mcan dive to 4000 m• 1964 – 20071964 – 2007• >4000 dives>4000 dives
manned submersiblemanned submersible• 6,500 m6,500 m
unmanned submersibleunmanned submersible• 11,000 m11,000 m
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http://www.csa.com/discoveryguides/vent/images/smoker.jpghttp://www.csa.com/discoveryguides/vent/images/smoker.jpghttp://whyfiles.org/coolimages/images/csi/nur04506.jpghttp://whyfiles.org/coolimages/images/csi/nur04506.jpg
““black smokers”black smokers”
20 m20 m
350350ooCC
2,800 m depth2,800 m depth
solutions exiting vents are acidic (pH = ~3.5) and contain up to 300 solutions exiting vents are acidic (pH = ~3.5) and contain up to 300 ppm ppm hydrogen sulfide (Hhydrogen sulfide (H22S) S)
• a highly reduced molecule, so much energy can be obtained when a highly reduced molecule, so much energy can be obtained when it is oxidizedit is oxidized
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http://www.divediscover.whoi.edu/images/vent_chemistry.jpghttp://www.divediscover.whoi.edu/images/vent_chemistry.jpg
““black smokers”black smokers”
seawater is heated and seawater is heated and reacts chemically with reacts chemically with the surrounding basaltthe surrounding basalt
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hydrothermal vent communityhydrothermal vent community
http://www.sciencedaily.com/images/2005/02/050223124700.jpghttp://www.sciencedaily.com/images/2005/02/050223124700.jpg
• includes snails, shrimps, includes snails, shrimps, crabs, crabs, tube wormstube worms, fishes , fishes and octopuses and octopuses
• depends on chemosynthetic depends on chemosynthetic bacteria for foodbacteria for food
chemosynthesischemosynthesis Tube wormsTube worms
deep-sea vent musselsdeep-sea vent mussels
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Hydrothermal vents are common on oceanic ridgesHydrothermal vents are common on oceanic ridges
http://www.nature.com/nature/journal/v439/n7079/images/hydro_vents/index.htmlhttp://www.nature.com/nature/journal/v439/n7079/images/hydro_vents/index.html
AND in freshwater (Lake Baikal)AND in freshwater (Lake Baikal)
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Abyssal plains and abyssal hills cover most of Abyssal plains and abyssal hills cover most of Earth’s surface.Earth’s surface.
Abyssal hillsAbyssal hills• small sediment-covered small sediment-covered extinct volcanos or rockextinct volcanos or rock
Abyssal plainsAbyssal plains• 40% of the ocean floor40% of the ocean floor• common in the Atlanticcommon in the Atlantic• rare in the Pacificrare in the Pacific• covered by sedimentcovered by sediment
FlatFlat
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Volcanic seamounts and guyots project above the seabedVolcanic seamounts and guyots project above the seabed
• about 30,000• about 10,000 in the Pacific
http://upload.wikimedia.org/wikipedia/en/thumb/2/25/Seamount_Locations.png/350px-Seamount_Locations.pnghttp://upload.wikimedia.org/wikipedia/en/thumb/2/25/Seamount_Locations.png/350px-Seamount_Locations.png
• >1 km in height>1 km in height• important fishing important fishing areasareas
Emperor Seamounts
seamountseamount
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blobfishblobfish
orange roughyorange roughy southern spinebacksouthern spineback
southern whiptailsouthern whiptail
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GuyotGuyot: : flat-topped seamount that once reached the surfaceflat-topped seamount that once reached the surface
http://en.wikipedia.org/wiki/Image:Guyot.jpghttp://en.wikipedia.org/wiki/Image:Guyot.jpg
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TrenchTrench: : arc-shaped depression on the deep-ocean floorarc-shaped depression on the deep-ocean floor
• occur near subduction zonesoccur near subduction zones
• deepest places in the oceandeepest places in the ocean
• most in the Pacificmost in the Pacifichttp://geology.com/records/ocean-trench.gifhttp://geology.com/records/ocean-trench.gif
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Peru-Chile Peru-Chile trenchtrench
http://en.wikipedia.org/wiki/Image:Peru-Chile_trench.jpghttp://en.wikipedia.org/wiki/Image:Peru-Chile_trench.jpg
Puerto Rico Puerto Rico trenchtrench
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Japan TrenchJapan Trench10,595 m10,595 m
Mariana TrenchMariana Trench11,022 m11,022 m
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TriesteTrieste
• reached the bottom of the Mariana reached the bottom of the Mariana Trench in 1960Trench in 1960
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Kaiko
• Japanese deep-sea submarineJapanese deep-sea submarine
• sampled bacteria from the bottom sampled bacteria from the bottom (10,897 m) of the Mariana Trench in (10,897 m) of the Mariana Trench in 19961996
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Sampling of the world's Sampling of the world's deepest sea sediment by deepest sea sediment by ""KaikoKaiko" at the Mariana " at the Mariana Trench, Challenger DeepTrench, Challenger Deep
Bacteria collected from the Mariana TrenchBacteria collected from the Mariana Trench
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• lost at sea in lost at sea in typhoon in 2003typhoon in 2003
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Key PointsKey Points
1. The ocean floor is mapped by 1. The ocean floor is mapped by bathymetrybathymetry..
2. Ocean-floor topography varies with 2. Ocean-floor topography varies with locationlocation..
3. Continental margins are “active” or 3. Continental margins are “active” or “passive”.“passive”.
4. The topology of deep-ocean basins differs 4. The topology of deep-ocean basins differs from that of the continental margin.from that of the continental margin.