Download The Oceans Ocean Floor Geologic Provinces Continental Margin

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The Oceans
• Major Ocean Basins:
– Pacific Ocean – largest and deepest
– Atlantic Ocean
– Indian Ocean – S. Hemisphere
– Arctic – smallest and most shallow
Ocean Floor Geologic Provinces
• Continental Margin
– Continental Shelf
– Continental Slope
– Continental Rise
• Ocean Basin Floor
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Abyssal Plain
Seamounts (previously discussed)
Oceanic Islands (previously discussed)
Deep Ocean Trenches (previously discussed)
• Mid-Ocean Ridges (previously discussed)
Geologic Provinces of the Ocean Basins
Turbidity Currents
Continental Margin
Ocean Basin Floor: Abyssal Plain, Seamounts,
Oceanic Islands
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Pacific Ocean Basin Seamount Chains
Deep Ocean Trench
Layered Structure of the Oceanic Crust & Upper
Mantle
• Ophiolite – Layered fragment of oceanic crust
emplaced onto the edge of continental crust
along a subduction zone
• Layer 1 = Sediment
– Terriginous – sand, silt and clay eroded from
continents
– Biogenous – Shells and skeletons of microscopic
marine animals and plants
– Hydrogenous – minerals precipitated from seawater
– Pelagic – Mixture of terriginous and biogenous
Atoll
Mid-Ocean Ridge
Ophiolite
• Layer 2 = Pillow Basalt – Forms when hot lava
comes into contact with cold water
• Layer 3 = Sheeted Dikes – Multiply intruded
dikes through which magma flowed toward
surface
• Layer 4 = Gabbro – Forms when mafic magma
crystallizes within magma chambers
• Layer 5 = Mantle Peridotite – Ultramafic rocks
which underwent partial melting to produce
mafic magmas
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Emplacement of Oceanic Crust onto
Continental Lithosphere
Sheeted Dike Complex - Oman
Layered Gabbro
Mantle Peridotite
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Chemical Composition of Ocean Waters
• Salinity – A measure of the amount of
dissolved salt in ocean waters.
– Average salinity = 35 o/oo (parts per mil)
– Most Abundant Salts: NaCl, MgCl2, Na2SO4,
CaCl2, KCl
– Sources of salts:
• Weathering and erosion of rocks on land
• Submarine volcanic eruptions
• Chemical interactions between seawater and hot,
newly formed ocean floor basalt
Processes Which Affect Salinity
• Processes Which Decrease Salinity:
– Biological (formation of shells)
– Precipitation
– Runoff from land
– Melting of glaciers and sea ice
• Processes Which Increase Salinity:
– Evaporation
– Freezing of water into glaciers and sea ice
Effects of Precipitation and Temperature on
Salinity
• Tropical Climates – Salinity is slightly
lower than 35 o/oo due to relatively high
amounts of rainfall
• Subtropical Climates – Salinity is slightly
higher than 35 o/oo due to relatively low
amounts of rainfall
• Polar Climates – Salinity is low due to low
solubility of salts in cold water
Ocean Water : Three-Layered Thermal
Structure
• Shallow-Surface Zone – Water is heated
by solar energy. Extends to depths up to
300 m.
• Transition Zone – Temperatures rapidly
decrease with depth (thermocline).
Extends to depths of approx. 1 km.
• Deep Zone – Water temperatures are just
above freezing.
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Tides - Primarily caused by gravitational attraction
of the Moon (and Sun) on the Ocean Basins
Spring Tide
• Spring Tide – Occurs when the Earth, Sun and
Moon are aligned (full moon, new moon).
Greatest difference between high tide and low
tide.
• Neap Tide – Occurs when the Moon is 90o out of
alignment with the Earth and Sun (first quarter
moon, third quarter moon). Smallest difference
between hight tide and low tide.
Neap Tide
Factors Which Affect Tidal Pattern: Shape of
Coastline, Configuration of Ocean Basin, Water
Depth
• Diurnal Tidal Pattern – Single high tide and
single low tide each 24 hour period (Gulf of
Mexico)
• Semidiurnal Tidal Pattern – Two high tides and
two low tides each 24 hour period, with each
high and low tide approximately the same height
(U.S. Atlantic Coast)
• Mixed Tidal Pattern – Two high tides and two
low tides each 24 hour period, with each high
and low tide of different heights (U.S. Pacific
Coast)
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Anatomy of a Wave in the Open Ocean
Wave Refraction, Longshore Current, Beach Drift
Shoreline Erosional Features: Wave-Cut Platform
Anatomy of a Breaking Wave
Shoreline Erosional Features: Wave-Cut Cliff
Shoreline Erosional Features: Marine Terrace
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Shoreline Erosional Features: Sea Arch
Shoreline Depositional Features: Spit
Shoreline Depositional Features: Tombolo
Shoreline Erosional Features: Sea Stack
Shoreline Depositional Features: Sandbar
Shoreline Depositional Features: Barrier Island
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Moving the lighthouse 1600 feet to its new home
Cape Hatteras Lighthouse (1870) - Prior to Move
Hard Stabilization – Construction of
structures to protect a coastline from erosion
• Groin – barrier built at right angles to the
beach to trap sand transported by
longshore current. Results in erosion of
sand down current of the groin.
• Sea Wall – Wall to protect beachfront
structures by reflection of wave energy
back toward the ocean. Results in rapid
erosion of beach sand.
Groin at base of Cape Hatteras
Lighthouse (former location)
Sea Wall
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Oceanic Circulation
Global Circulation - Gyres
• Gyre – an open ocean current
– Circular path
– Clockwise N. Hemisphere; Counterclockwise
S. Hemisphere
– Driven by descending winds at ~ 30o N and S
– Each consists of separate currents
– Five main gyres: North Pacific, South Pacific,
North Atlantic, South Atlantic Indian
Coriolis Effect
• The deflection of currents to the right (N.
Hem.) or left (S. Hem.) of their path of
motion.
– Caused by the rotation of the solid Earth
underneath a current attempting to move
between two points on the Earth’s surface
• Results in rotation of gyres in clockwise direction
N. Hemisphere and counter clockwise direction S
hemisphere
Deep-Sea Currents
• Driving force is density of ocean waters
– Cold, polar waters sink and move toward
equator
– Warm, equatorial waters rise and move
toward poles
– Global conveyor belt effect
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Coastal Upwelling
• Coastal zone where cold water is
transported upward along the coast
– Usually occur where atmospheric circulation
blows warm water away from the coastline,
allowing cold waters to rise
– Important nutrient-rich fishing grounds
– Example: west coast of S. America
Coastal Classification
• Emergent Coastline – develops due to uplift of
coast and/or drop in sea level
– Wave-cut cliffs, marine terraces, sea arches, sea
stacks
– Example: coastal California
• Submergent Coastline – develops as a results of
a rise in sea level
– Submerged river valleys (estuaries, bays), headlands
– Example: Chesapeake and Delaware Bays, Delmarva
Peninsula
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