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

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)

I Continental Margin (cont.)

•Continental SlopeSteeper (2-6o) 300-8,000m depth Submarine canyons

•Continental RiseSubmarine fans TurbiditesOil & gas reservoirs

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)

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

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

I Sediments are Sampled by

•Grabs (hand sample, clamshell)

•Cores (box, piston)

•Drilling

II Value of Sediment/Sedimentary Rocks

•Archive of Earth history- Evolution/extinction - Climate change - Creation/destruction of

ocean basins

•Hydrocarbon reservoirs

•Metallic mineral deposits

III Classification – based on…

•Origin

- Clastic or chemical - Biotic or inorganic

•Texture – Appearance

- Size, sorting, - Shape, rounding - Grain-matrix relationships

•Composition

- Mineralogy - Biotic components

IV Types/Sources

•Terrigenous / clastic – from continents

•Chemical / precipitate - form in ocean basins

- Biogenous - organic

- Hydrogenous - inorganic

•Cosmogenous - from space

IV Types/Sources (cont.)

Terrigenous/clastic – from continents

•Conglomerate, breccia

•Sandstone

•Siltstone

•Shale / mudstone / red clays

Clastic sediments are classified by particle size

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

IV Types/Sources (cont.)

Cosmogenous - from space

•Glass spherules•Tektites

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

VI Distribution of Sediment Types

•Patterns

•Controls- Energy levels- Depth- Latitude- Source

GEOLOGY OF THE WORLD’S OCEANS

Physical Properties of Seawater

I Origin

II The Marvelous Water Molecule: H2O

III Physical properties

IV Energy transmission

•Volcanic outgassing

•Comets

I Origin

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”

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)

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

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

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

I Water Chemistry Measured/ Sampled By

CTD (Measures conductivity, temperature, depth)

Niskin bottles retrieve water samples

II Composition

•Dissolved gases

•Dissolved solids

•Particulates (clays and organic matter)

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

Oceanic gasesare mainly CO2and O2

Note changes inconcentration with increasingdepth -

Why?

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

- Nutrients

•Important for growth

•Concentrated in ocean bottom waters

•Supplied to surface waters through

Upwelling

Rivers

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

II Composition (cont.)

- Particulates (Clays and Organic Matter)

•Scatter light

•Raise depth of photiczone

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

IV Chemical Properties

•Universal solvent

•Catalyst

Why?

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

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

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

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)

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)

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

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

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

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)

III Currents Influenced By

•Continents – e.g. pile up on western side of ocean basins

•Submarine features – e.g. mid- ocean ridges

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

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

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

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

•Wave height (H)•Wave length (λ)•Wave period (P)•Crest

•Trough •Swells •Open-ocean waves•Shallow-water waves

I Anatomy of a Wave

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

III Capable of Erosion, Transport and Deposition of Sediment

•Erosion

•Entrainment & Transport of Grains

•Sedimentary Structures

•Land Forms

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

III Erosion (cont.)

Entrainment of grains

•Size•Mass•Shape•Flow velocity

III Transport of Sediment

•Swash & backwash

•Beach drift

•Long shore drift

•Rip “tides”

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

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)

VI Waves as Energy Sources

•Lift objects

•Use orbital motion

•Compress air in cylinders

•Difficulties - unpredictable timing- possibly too strong

Ocean Tides

I Mechanism

II Timing

III Effects

IV Energy from Tides

GEOLOGY OF THE WORLD’S OCEANS

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)

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

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”

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