Ocean Basins
description
Transcript of Ocean Basins
Ocean Ocean BasinsBasins
Structure of the OceansStructure of the OceansFrom Continental Shelf toFrom Continental Shelf to
Abyssal DepthsAbyssal Depths
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Measuring DepthMeasuring Depth
85 BC Posidonius ~2km85 BC Posidonius ~2km Hemp line and greased lead weightHemp line and greased lead weight
tensiontension Fathoms (6 feet)Fathoms (6 feet)
Piano wire and cannonball w/ winchPiano wire and cannonball w/ winch By 1895 only 7000 measurements to 2000m and 550 By 1895 only 7000 measurements to 2000m and 550
to >9000mto >9000m Echo sounder (depth recorder) 1920sEcho sounder (depth recorder) 1920s
MeteorMeteor- mid-Atlantic ridge- mid-Atlantic ridge 1950s detailed mapping of ridges and trenches1950s detailed mapping of ridges and trenches
Heezen and TharpHeezen and Tharp
Echo Sounder
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BathymetryBathymetry
LADS (shallow water)LADS (shallow water) Laser airborne depth sounderLaser airborne depth sounder Fixed winged aircraft/ GPSFixed winged aircraft/ GPS Operating depth of 0.5-70mOperating depth of 0.5-70m
Gravity measurementsGravity measurements Changes in sea surface elevationChanges in sea surface elevation
Seamounts +5m and ridges +10mSeamounts +5m and ridges +10m Trenches -25-30mTrenches -25-30m
Satellite altimetrySatellite altimetry Side-scan sonarSide-scan sonar
Marine Gravity Anomalies by Satellite Altimetry
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Bathymetry of the Sea FloorBathymetry of the Sea Floor
Continental Margin- Passive and ActiveContinental Margin- Passive and Active Continental shelf (Flat- 10-1500km, 65km; 20-Continental shelf (Flat- 10-1500km, 65km; 20-
500m deep)500m deep) Continental shelf breakContinental shelf break
Continental slope (Steep)Continental slope (Steep) Submarine canyonsSubmarine canyons
Turbidity currents and turbiditesTurbidity currents and turbidites
Continental riseContinental rise
Ocean FloorOcean Floor Ridges, Rises and TrenchesRidges, Rises and Trenches
Shelf BreakSlope
Rise
Computer Drawn Topographic Profiles
Mid-Atlantic ridge
Continental Shelves
Formation of Shelves by trapping of land derived sediments
Turbidity Currents- 90km/hr, 300kg of sed in suspension
Submarine Canyon
Ancient Turbidite SequenceBouma SequenceTop- (E)Pelagic Seds
(D)Parallel Laminated Sands
(C)Rippled, wavy or convoluted laminae
(B)Plane Parallel LaminaeBottom-(A)Massive Graded
D
C
A
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Bathymetry of the Sea FloorBathymetry of the Sea Floor Ocean FloorOcean Floor
Deep seafloor (4000-6000m cover 30% of Deep seafloor (4000-6000m cover 30% of Earth’s surface)Earth’s surface)
Abyssal Plain (Flat)Abyssal Plain (Flat) Pelagic sediments and turbiditesPelagic sediments and turbidites
Abyssal hills and seamounts & GuyotsAbyssal hills and seamounts & Guyots <1000m high; steep sided volcanoes<1000m high; steep sided volcanoes Found on 50% Atlantic and 80% Pacific seafloorFound on 50% Atlantic and 80% Pacific seafloor Some become atollsSome become atolls
Ridges, Rises and TrenchesRidges, Rises and Trenches 65,000km mountain range65,000km mountain range Challenger Deep (Mariana Trench 11,020m)Challenger Deep (Mariana Trench 11,020m)
Major Ocean Basins
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SedimentsSediments
Continental margins and ocean basins receive Continental margins and ocean basins receive continuous supplycontinuous supply
OrganicOrganic planktonplankton
Terrigenous (Land)Terrigenous (Land) Rivers, beachesRivers, beaches
AtmosphericAtmospheric windwind
SpaceSpace tektites (meteorites)tektites (meteorites)
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Continental MarginContinental Margin
Thick Sequence of sediments (1000’s m)Thick Sequence of sediments (1000’s m) Passive marginPassive margin
Gravels, sands, mudsGravels, sands, muds Rates of deposition vary 8m/yr in estuariesRates of deposition vary 8m/yr in estuaries 5m/1000yr quiet bays5m/1000yr quiet bays Shelf and slope 10-40cm/1000yrsShelf and slope 10-40cm/1000yrs
CarbonatesCarbonates SaltsSalts Potential for resourcesPotential for resources
OilOil GasGas Methane HydratesMethane Hydrates
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Sand and GravelSand and Gravel
1.2 billion tons/yr1.2 billion tons/yr Reserves of 800 billion tonsReserves of 800 billion tons
US 450 billion tonsUS 450 billion tons
UK & Japan take 20% from seafloorUK & Japan take 20% from seafloor Other materials found within such as Fe, Other materials found within such as Fe,
U, Pt, Au & DiamondU, Pt, Au & Diamond The Tin Belt of SE AsiaThe Tin Belt of SE Asia Carbonate sandsCarbonate sands
Oil and Gas account for 95% of material exploited from the sea24.8% of oil and 20.7% gas in US came from offshore production (1997)
Gas Hydrates and other Gases
• Geopressurized zones• Methane Hydrates, crystalline
solids of gas and water abundant in arctic regions and marine sediments
• 1 ft3 releases 160 ft3 gas• Offshore east coast area of
potentially 1300 trillion ft3 gas• Reserves 4x1020 ft3
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Atmosphere-WindAtmosphere-Wind
Winds from deserts transfer terrigenous Winds from deserts transfer terrigenous sediment 1000’s kms into ocean basinsediment 1000’s kms into ocean basin
Annual supply to oceans 100x10Annual supply to oceans 100x1066 metric metric tonstons
Sahara-Caribbean connectionSahara-Caribbean connection ReefsReefs SoilsSoils
Sorting
Poorly Well
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Biogenous SedimentBiogenous Sediment Planktonic- Siliceous and Carbonate OozesPlanktonic- Siliceous and Carbonate Oozes
PhytoplanktonPhytoplankton Diatoms (silica)Diatoms (silica) Coccolithosphorids (carbonate)Coccolithosphorids (carbonate)
ZooplanktonZooplankton Radiolarians (silica)Radiolarians (silica) Foraminefera (carbonate)Foraminefera (carbonate)
Lysocline (dissolution)Lysocline (dissolution) CCD (carbonate compensation depth) <20% CCD (carbonate compensation depth) <20%
preservation CO3 ~4500mpreservation CO3 ~4500m Atlantic (5000m)Atlantic (5000m) Pacific (4200-4500m); Equatorial Pacific (5000m)Pacific (4200-4500m); Equatorial Pacific (5000m)
Diatoms Coccolithosphorids
Radiolarians
Foraminifera
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Hydrogenous SedimentHydrogenous Sediment Slow formation in water columnSlow formation in water column Chemically precipitatedChemically precipitated
Carbonates (ooids, calcareous muds)Carbonates (ooids, calcareous muds) Phosphorites (fertilizers)Phosphorites (fertilizers)
Continental shelf and slopeContinental shelf and slope Reserve ~ 50 billion tonsReserve ~ 50 billion tons Nodules or crustsNodules or crusts Due to high nutrients-upwellingDue to high nutrients-upwelling
Salts (Mediterranean)Salts (Mediterranean) Manganese nodulesManganese nodules
Concentric layeringConcentric layering High in Fe, Cu alsoHigh in Fe, Cu also 1-10cm diameter1-10cm diameter
Hydrothermal vents (smokers)-ores (sulfides)Hydrothermal vents (smokers)-ores (sulfides)
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UpwellingUpwelling When wind blow offshore, they When wind blow offshore, they push the warm surface waters push the warm surface waters away from the coastlineaway from the coastline
This creates a region of low This creates a region of low pressure and may result in pressure and may result in upwelling of deep water to upwelling of deep water to replace surface water.replace surface water.
The deep waters contain The deep waters contain dissolved nutrients which can dissolved nutrients which can support abundant life at the support abundant life at the surfacesurface
Many fishing grounds exist in Many fishing grounds exist in these areas, notably the west these areas, notably the west coast of N. & S.coast of N. & S. America and w America and w coast of Africacoast of Africa
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Laws and TreatiesLaws and Treaties
200-mile EEZ200-mile EEZ Law of the Sea (1982)Law of the Sea (1982)
All wealth is shared by humanityAll wealth is shared by humanity Regulated by UNRegulated by UN Profits sharedProfits shared US did not sign treatyUS did not sign treaty
Provisional Understanding Regarding Deep Provisional Understanding Regarding Deep Seabed Matters (1984)- Western countries (US, Seabed Matters (1984)- Western countries (US, UK, Germany, Japan…)UK, Germany, Japan…) 4 consortia awarded exploration licenses4 consortia awarded exploration licenses
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Sediments as RecordsSediments as Records
PaleoceanographyPaleoceanography Isotopic studiesIsotopic studies
Oxygen isotope ratios in skeletal material to Oxygen isotope ratios in skeletal material to infer past climate (infer past climate (1818O:O:1616O)O)
Dependant on ratio in seawaterDependant on ratio in seawater During glaciations is During glaciations is 1616O removed, so O removed, so 1818O:O:1616O O
ratio increases in seawaterratio increases in seawater
Marine plankton distributionMarine plankton distribution Circulation modelsCirculation models