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, sedimentation
Broad
•Pacific Type (Leading Edge -Active) –
Volcanism, deformation, uplift
Narrow
•Continental Shelves
Gentle, < 1o (1:500) slope
30m-1300km wide
Break at ~ 130m depth
•Epeiric Seas (In Past)
1:50,000 slope
Very broad (1,000s of km)
I Continental Margin (cont.)
•Continental Slope
Steeper (2-6o)
300-8,000m depth
Submarine canyons
•Continental Rise
Submarine fans
Turbidites
Oil & 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
GEOLOGY OF THE WORLD’S OCEANS
Ocean Sediments
I Sampled by…
II Value
III Classification
IV Types/Sources
V Effects on Organisms
VI Distribution of Sediment
Types
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 and
may impact photosynthesis
•High turbidity may interfere with
suspension feeding
•High sedimentation may bury
sessile bottom dwellers
•Fine sediment may preserve carbon
for deposit feeders
•Fine sediment may be oxygen poor
and 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
I Origin
•Volcanic outgassing
•Comets
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
“universal
solvent”
III Physical properties
•States - solid, liquid, gaseous
Volume change with phase change
•Density - 1g/cm3 @ 4oC
Affected by temperature
Affected 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 gases
CO2, 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 gases
are mainly CO2
and O2
Note changes in
concentration
with increasing
depth 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”
•Traces
I, Ba, Li, Cu, Ni, Se, Zn, others
Can be important to organisms, e.g. iodine
•Nutrients
Si, N, P
Measured 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, echinoderms
euryhaline snails, clams, algae
II Composition (cont.)
- Particulates (Clays and Organic Matter)
•Scatter light
•Raise depth of photic
zone
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 Effect
On a rotating sphere, velocity varies (e.g.
equator, 850km/hr at 60oN)
1700km/hr at
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
change
phase
•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
•Energy loss due to: Moving over land, moving into cooler waters
•Damage due to: Wind (120 - 250 km/hr), floods, storm surge
life
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
I Anatomy of a Wave
•Wave height (H)
•Wave length (λ)
•Wave period (P)
•Crest
•Trough
•Swells
•Open-ocean waves
•Shallow-water waves
II Mechanisms
•Energy from wind
Velocity, duration, distance (fetch)
•Surface cohesion important
•Water moves in circular orbits
- Orbital diameter decreases with depth
- Orbits “feel” bottom at depth ~ ½ λ
Orbits become more elliptical
Wave length decreases
Wave height increases
Breakers form
III Capable of Erosion, Transport
and Deposition of Sediment
•Erosion
•Entrainment & Transport of Grains
•Sedimentary Structures
•Land Forms
III Erosion (cont.)
Erosion
Major destructive force in coastal settings
•Pressure and abrasion
•Energies concentrated by refraction
•Influenced by bedrock vs
unconsolidated sediments
•Combated with jetties, sea walls,
breakwaters, beach nourishment
III Erosion (cont.)
III Transport of Sediment
Entrainment of grains
•Swash & backwash
•Size
•Mass
•Shape
•Flow velocity
•Beach drift
•Long shore drift
•Rip “tides”
III Sedimentary Structures (small-scale features)
•Oscillation/ symmetrical ripples
•Asymmetrical/ current ripples
•Dunes
and Forms (large-scale features)
•Erosional
- Wave cut terraces and sea cliffs
- Sea arches and stacks
•Depositional
- Spits
- Barrier islands
- Bay mouth bars
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
GEOLOGY OF THE WORLD’S OCEANS
Ocean Tides
I Mechanism
II Timing
III Effects
IV Energy from Tides
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 sediment
Tidal 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 migration
of marine life