Morphology Of Ocean Basins - Utah State University · Morphology Of Ocean Basins. ... Measured in...
Transcript of Morphology Of Ocean Basins - Utah State University · Morphology Of Ocean Basins. ... Measured in...
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Morphology Of Ocean Basins
I Continental Margin•Continental Shelves •Epeiric Seas (In Past)•Continental Slope•Continental Rise
II Ocean Basin•Mid Ocean Ridges, Rises, Fracture Zones•Abyssal Plains, Hills, Seamounts•Trench/Subduction Zones•Island Arcs•Back Arc Basins
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I Continental Margin
•Atlantic Type (Trailing Edge -Passive) –Subsidence, sedimentationBroad
•Pacific Type (Leading Edge -Active) –Volcanism, deformation, upliftNarrow
•Continental Shelves Gentle, < 1o (1:500) slope30m-1300km wideBreak at ~ 130m depth
•Epeiric Seas (In Past)1:50,000 slopeVery broad (1,000s of km)
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I Continental Margin (cont.)
•Continental SlopeSteeper (2-6o) 300-8,000m depth Submarine canyons
•Continental RiseSubmarine fans TurbiditesOil & gas reservoirs
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II Ocean Basins
•Abyssal Plains, Hills, Seamounts- Plains <1:1000 slope, 4-6km depth
30% earth’s surface area (= total continental area)- Hills < 1000m relief- Seamounts are submerged volcanoes with high relief
may be flat topped (guyots)
•Mid Ocean Ridges, Rises, Fracture Zones- Vent communities, deep circulation and
chemical reactions- Relation between spreading rates and rise slope
(Pacific 10cm/yr, 0.1o slope; Atlantic 2-3cm/yr, 1o slope)
- Locally high relief (1,000m cliffs)
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II Ocean Basins (cont.)
•Trench/Subduction Zones- Up to 4o slopes- Mariana 11km (36,000’) deep - Peru-Chili 6,000 km long
•Island Arcs
•Back Arc Basins
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I Sampled by…
II Value
III Classification
IV Types/Sources
V Effects on Organisms
VI Distribution of Sediment Types
GEOLOGY OF THE WORLD’S OCEANSOcean Sediments
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I Sediments are Sampled by
•Grabs (hand sample, clamshell)
•Cores (box, piston)
•Drilling
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II Value of Sediment/Sedimentary Rocks
•Archive of Earth history- Evolution/extinction - Climate change - Creation/destruction of
ocean basins
•Hydrocarbon reservoirs
•Metallic mineral deposits
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III Classification – based on…
•Origin
- Clastic or chemical - Biotic or inorganic
•Texture – Appearance
- Size, sorting, - Shape, rounding - Grain-matrix relationships
•Composition
- Mineralogy - Biotic components
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IV Types/Sources
•Terrigenous / clastic – from continents
•Chemical / precipitate - form in ocean basins
- Biogenous - organic
- Hydrogenous - inorganic
•Cosmogenous - from space
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IV Types/Sources (cont.)
Terrigenous/clastic – from continents
•Conglomerate, breccia
•Sandstone
•Siltstone
•Shale / mudstone / red clays
Clastic sediments are classified by particle size
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IV Types/Sources (cont.)
Chemical/precipitate - form in ocean basins
Biogenous – organic
•Limestone/calcareous oozes CaCO3 –from forams & coccoliths –important sink for CO2
•Chert/siliceous oozes SiO2 –from radiolaria & diatoms, volcanic ash
Hydrogenous – inorganic
•Phosphates - ~CaPO4•Manganese - MnO2•Evaporites - Gypsum CaSO4, halite NaCl
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IV Types/Sources (cont.)
Cosmogenous - from space
•Glass spherules•Tektites
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V Sediment Effects on Organisms
•High turbidity reduces light levels andmay impact photosynthesis
•High turbidity may interfere with suspension feeding
•High sedimentation may burysessile bottom dwellers
•Fine sediment may preserve carbonfor deposit feeders
•Fine sediment may be oxygen poorand inhospitable for infauna
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VI Distribution of Sediment Types
•Patterns
•Controls- Energy levels- Depth- Latitude- Source
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GEOLOGY OF THE WORLD’S OCEANS
Physical Properties of Seawater
I Origin
II The Marvelous Water Molecule: H2O
III Physical properties
IV Energy transmission
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•Volcanic outgassing
•Comets
I Origin
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II The Marvelous Water Molecule: H2O
•Covalent bonds between H and O
•Polar molecule (ends carry charges)
•Hydrogen bonds between molecule(very strong)
Water is the“universalsolvent”
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III Physical properties
•States - solid, liquid, gaseousVolume change with phase change
•Density - 1g/cm3 @ 4oCAffected by temperatureAffected by dissolved solids
•Relatively incompressible (1.7% at 400 atm = 37m lowering of oceans)
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III Physical properties (cont.)
•High heat capacity
- Water 1.0 cal/g/oC, alcohol 0.23, lead 0.03
•Relatively high melting (0oC) and boiling (100oC) points
- Affected by dissolved solids- Affected by atmospheric pressure
•Viscous
•Capillarity/surface tension
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IV Energy transmission
•Light- Long wavelength (red) absorbed quickly- Short wavelength (blue) penetrates deeper- Great attenuation due to absorption and scatter- Refracted (bent)
•Sound- Transmitted much better than in air
(1500m/sec, 5 X faster)- Faster in warm water, faster under increased
pressure
•Heat- Inefficiently transferred downward through
conduction
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GEOLOGY OF THE WORLD’S OCEANS
Chemical Properties of Seawater
I Sampled by…
II Composition
III Cycling of Dissolved Substances in Sea Water
IV Chemical Properties
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I Water Chemistry Measured/ Sampled By
CTD (Measures conductivity, temperature, depth)
Niskin bottles retrieve water samples
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II Composition
•Dissolved gases
•Dissolved solids
•Particulates (clays and organic matter)
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II Composition (cont.)
- Dissolved gasesCO2, N2 , O2
•Concentrations differ from atmosphere
•CO2 and O2 will affect the distribution of organisms
•CO2 will affect ph and dissolution/precipitation of minerals (e.g. CCD)
•Gas concentrations vary with depth - why?
•Gas solubility is affected by water temperature
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Oceanic gasesare mainly CO2and O2
Note changes inconcentration with increasingdepth -
Why?
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II Composition (cont.)
- Dissolved solids (total = salinity = 3.5 % or 35 ppt o/oo, not 35 %(e.g. 35 gm salt per 1.0 liter water)
•Major constituents (99.4% of dissolved solids)Cl, Na, SO4, Mg, Ca, K Measured in ppt -- “Conservative”
•TracesI, Ba, Li, Cu, Ni, Se, Zn, othersCan be important to organisms, e.g. iodine
•NutrientsSi, N, PMeasured in ppb -- “Nonconservative”Required for growth – influence marine productivity
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- Nutrients
•Important for growth
•Concentrated in ocean bottom waters
•Supplied to surface waters through
Upwelling
Rivers
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II Composition (cont.)
- Dissolved solids
•Salinity varies with latitude and depth - why?
•Salinity varies with environments e.g. hypersaline and hyposaline environments
•Organisms vary in their ability to tolerate excursions from “normal marine”
e.g. stenohaline corals, echinodermseuryhaline snails, clams, algae
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II Composition (cont.)
- Particulates (Clays and Organic Matter)
•Scatter light
•Raise depth of photiczone
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III Cycling of Dissolved Substances in Sea Water
•Added by- Volcanic outgassing- Reactions at mid ocean ridges
and fracture zones - Weathering of continental rocks- Weathering of marine rocks- Marine life (photosynthesis, respiration)
•Removed by- Biotic processes (esp Ca and Si)- Evaporite deposits- Sea spray - Adsorption onto clays
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IV Chemical Properties
•Universal solvent
•Catalyst
Why?
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GEOLOGY OF THE WORLD’S OCEANS
The Atmosphere
•Gaseous envelope surrounding our planet - energized by solar radiation
•Generated by volcanic outgassing and biologic processes (photosynthesis).
•Has evolved over time – initially CO2, H?, N rich
•Oxygenated (1% PAL) by 2.0 Ga
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I Earth’s Heat Budget
•Insolation varies with latitude
•Water has high heat capacity
•62% of solar energy absorbed at earth’s surface is transferred to atmosphere through evaporation
•Oceans show relatively little fluctuation in surface temperatures
•Oceans moderate terrestrial climates
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II Atmospheric Circulation Models
(Note -warm air less dense, humid air less dense)
1) Non-rotating, water-covered Earth(no continents)
2) Rotating, water-covered Earth(no continents)
3) Rotating, with oceans and continents
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II Atmospheric Circulation Models
1) Non-rotating, water-covered earth (no continents)
• Latitudinally-controlled temperature differences
• Simple cells with N surface winds in northern hemisphere (winds named based on where
they are from)
2) Rotating, water-covered earth (no continents)
• Coriolis EffectOn a rotating sphere, velocity varies (e.g. 1700km/hr at equator, 850km/hr at 60oN)
• Generates 6 cells (e.g. Hadley cells) - gives surface winds (Westerlies, Trades) separated by zones of vertical movement (Doldrums and Horse Latitudes)
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II Atmospheric Circulation Models (cont.)
3) Rotating, with oceans and continents
•At mid latitudes, seasonal difference between land and oceans drive winds/pressure systems (e.g. high over cool continents, low over warm oceans) flow is from high to low
•Monsoons - spring time, continents warm more rapidly, cool oceanic air flows landward, rises and releases water
•Lows spawn hurricanes/cyclones
•Daily patterns Sea-Land Breezes (e.g. “Undertaker Wind”) Mountain-Valley Winds (e.g. local canyon winds)
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III Storms
Cyclones (Indian Ocean), Typhoons (W. Pacific), Hurricanes (Atlantic, E. Pac.), Willi-Willis (Australia)
•Form between 10o-25o lat.; Require warm, moist air
•Established over lows, draw heat energy from water phase change
•Circulate ccw in N hemis., cw in S hemis. (Coriolis gives spin)
•Move at 5-40km/hr;1000 km wide; 15 km high; 5-10 days avg life
•Energy loss due to: Moving over land, moving into cooler waters
•Damage due to: Wind (120 - 250 km/hr), floods, storm surge
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GEOLOGY OF THE WORLD’S OCEANS
Ocean Circulation
I Layered Oceans
II Mechanisms
III Influenced By
IV Current Types
V Surface Current Zones
VI El Nino (ENSO) and La Nina
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I Layered Oceans
•Subsurface masses of different densities
- Due to a combination of salinity and temperature (and pressure)
- Salinity and temperature controlled by climate at surface (related to latitude)
- Pycnocline, thermocline or halocline may separate water masses
•Mixed surface zone (down to ~ 100m)
- Due to wave action - Temperature, oxygen, salinity relatively
constant
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II Mechanisms
•Wind
- Surface cohesion of water (due to hydrogen bonds)- Considerable inertia- Ekman spiral
•Density differences (thermohaline circulation)
- Temperature- Salinity
•Tides (attraction of sun and moon)
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III Currents Influenced By
•Continents – e.g. pile up on western side of ocean basins
•Submarine features – e.g. mid- ocean ridges
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IV Current Types
•Surface Currents – wind generated, relatively rapid
•Deep Currents – thermohaline, carry O2
- North Atlantic Deep Water NADW
- Antarctic Bottom Water AABW
•Vertical Currents – slow,
- Upwelling with divergence (supply nutrients)
- Downwelling with convergence
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V Surface Currents
•Gyres
- Boundary Currents (with western intensification)
- Western currents - narrow, deep, fast (e.g. The Gulf Stream)
- Eastern currents - broad, shallow, slow (e.g. The California Current)
•Ekman Spiral
•Equatorial Counter Current
•Convergence Zones
•Divergence Zones
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VI El Nino (ENSO) and La Nina
•Influence weather in western hemisphere
•Control ocean productivity off South America
•Driven by changing high/low pressure zones in Pacific
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GEOLOGY OF THE WORLD’S OCEANS
Waves
I Anatomy of a Wave
II Mechanisms
III Capable of Erosion, Transport and Deposition
IV Giant Waves/Rogue Waves
V Tsunamis/Seismic Sea Waves – not tidal waves
VI Waves as Energy Sources
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•Wave height (H)•Wave length (λ)•Wave period (P)•Crest
•Trough •Swells •Open-ocean waves•Shallow-water waves
I Anatomy of a Wave
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II Mechanisms
•Energy from windVelocity, duration, distance (fetch)
•Surface cohesion important
•Water moves in circular orbits
- Orbital diameter decreases with depth
- Orbits “feel” bottom at depth ~ ½ λOrbits become more ellipticalWave length decreasesWave height increasesBreakers form
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III Capable of Erosion, Transport and Deposition of Sediment
•Erosion
•Entrainment & Transport of Grains
•Sedimentary Structures
•Land Forms
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III Erosion (cont.)
ErosionMajor destructive force in coastal settings
•Pressure and abrasion
•Energies concentrated by refraction
•Influenced by bedrock vsunconsolidated sediments
•Combated with jetties, sea walls, breakwaters, beach nourishment
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III Erosion (cont.)
Entrainment of grains
•Size•Mass•Shape•Flow velocity
III Transport of Sediment
•Swash & backwash
•Beach drift
•Long shore drift
•Rip “tides”
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and Forms (large-scale features)
•Erosional- Wave cut terraces and sea cliffs- Sea arches and stacks
•Depositional- Spits- Barrier islands- Bay mouth bars
III Sedimentary Structures (small-scale features)
•Oscillation/ symmetrical ripples
•Asymmetrical/ current ripples
•Dunes
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IV Giant Waves/Rogue Waves
•Wave energies concentrated, additive effects•In open ocean often at the shelf edge –
esp. S. Africa•Up to 58m high, 50 km/hr speeds•May break large ships
V Tsunamis/Seismic Sea Waves(Not tidal waves)
•Generated by earthquakes and landslides•Travel quickly across ocean basins•Long wavelength waves(λ 200km, H 0.5m, P 20 min, V 760km/hr)
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VI Waves as Energy Sources
•Lift objects
•Use orbital motion
•Compress air in cylinders
•Difficulties - unpredictable timing- possibly too strong
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Ocean Tides
I Mechanism
II Timing
III Effects
IV Energy from Tides
GEOLOGY OF THE WORLD’S OCEANS
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I Mechanism
•Interaction with moon and sun’s gravity
•Centrifugal/inertial forces
•Ellipticity of earth and moon’s orbits
•Declination of moon and sun relative to earth
•Influenced by shape of ocean basins
•Focused by local topography (e.g. tidal bores up rivers)
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II Timing•Daily
- Diurnal - 1 high, 1 low- Semidiurnal - 2 equal highs, 2 equal lows- Semidiurnal mixed - 2 unequal highs,
2 unequal lows
Tides arrive 50 min later each day – why?
•Monthly
Spring Tides - constructive (additive) effect of sun and moon, occurs with new and full moon
Neap Tides - destructive effect of sun and moon, occurs with first and third quarter moon
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III Effects
•Influenced by tidal range and topography (gentle or steep)
•Expose sea floor, cause pronounced zonation
-Supratidal zone-Intertidal zone - Subtidal zone
•Generate strong currents
- Carry food and nutrients
- Erode and transport sedimentTidal channels Ripples/dunes “Herringbone”
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IV Energy from Tides
•Water wheels/mills
Proven technology in North Sea
•Turbines - Require sufficient tidal range and dams
Downside – may restrict migrationof marine life