Lecture #6Lecture #6

Continental Margins Continental Margins and Ocean Basinsand Ocean Basins

22 August 200722 August 2007

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

http://www.the-planet-mars.com/map-of-http://www.the-planet-mars.com/map-of-mars.htmlmars.html

• 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

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.

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.

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

Scientists now use beams of sound to measure depth.Scientists now use beams of sound to measure depth.

Scientists now use beams of sound to measure depth.Scientists now use beams of sound to measure depth.

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

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”

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”

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”

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”

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.

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

World Ocean FloorWorld Ocean Floor

http://www.panorama-map.com/Europeans/Berann/berannpacificocean500.htmlhttp://www.panorama-map.com/Europeans/Berann/berannpacificocean500.html

Pacific OceanPacific Ocean

http://www.berann.com/panorama/Everest.jpghttp://www.berann.com/panorama/Everest.jpg

Mt. Everest Mt. Everest (1962)(1962)

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

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

  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

Sea surface

SeafloorSeafloor

？？Sea surface

SeafloorSeafloor

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

Geosat satelliteGeosat satellite

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

Ocean-floor topography varies with locationOcean-floor topography varies with location

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

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

• 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

Three main parts of the continental margin:Three main parts of the continental margin:

Continental shelfContinental shelf: : shallow submerged extension of a continent shallow submerged extension of a continent

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

http://www.cryingvoice.com/Evolution/gifs/hydroNA.jpghttp://www.cryingvoice.com/Evolution/gifs/hydroNA.jpg

AtlanticAtlantic

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.

Continental shelves are greatly influenced by Continental shelves are greatly influenced by changes in sea levelchanges in sea level

Sea level riseSea level rise

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

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

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

Bering StraitBering Strait

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

Bering StraitBering Strait

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

Allowed human migration 12,000 years ago

Bering StraitBering Strait

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

http://cocos.arecaceae.com/indo19.gifhttp://cocos.arecaceae.com/indo19.gif

Ice age sea level in AsiaIce age sea level in Asia

Continental slopes connect continental shelves to the Continental slopes connect continental shelves to the deep-ocean floordeep-ocean floor

shelf break

Submarine canyons form at the junction between continental Submarine canyons form at the junction between continental shelf and continental slope.shelf and continental slope.

http://www.tahoemaps.com/files/Monterey_large.jpghttp://www.tahoemaps.com/files/Monterey_large.jpg

Monterey Bay canyonMonterey Bay canyon

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

Suruga BaySuruga Bay

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.

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

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.

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

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

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

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

IcelandIceland

fracturefracture

15 cm/year15 cm/yearhttp://library.thinkquest.org/C003124/images/diverg.jpghttp://library.thinkquest.org/C003124/images/diverg.jpg

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

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

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

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

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

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

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

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)

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

  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

blobfishblobfish

orange roughyorange roughy southern spinebacksouthern spineback

southern whiptailsouthern whiptail

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

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

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

Japan TrenchJapan Trench10,595 m10,595 m

Mariana TrenchMariana Trench11,022 m11,022 m

TriesteTrieste

• reached the bottom of the Mariana reached the bottom of the Mariana Trench in 1960Trench in 1960

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

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

• lost at sea in lost at sea in typhoon in 2003typhoon in 2003

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.