The ocean
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The Ocean. EARTH: The only planet w/ Oceans (or liquid water) Covers 71% of earth’s surface “Divided” into 4 large basins Pacific (largest, deepest) Atlantic Indian Arctic (smallest, shallowest) A fifth? The Antarctic…. Ocean basins. South pole view. Ocean Basin Depths.

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The Ocean

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The Ocean

  • EARTH: The only planet w/ Oceans (or liquid water)

  • Covers 71% of earth’s surface

  • “Divided” into 4 large basins

    • Pacific (largest, deepest)

    • Atlantic

    • Indian

    • Arctic (smallest, shallowest)

    • A fifth? The Antarctic…


Ocean basins

South pole view


Ocean Basin Depths


Interior of Earth


The Difference Between an Ocean and a Continent…ROCKS!

  • Continent: very thick, very old, less dense and made up of Granite

  • Ocean (floor): younger, more dense, not as thick and made up of Basalt

  • Thus, the “Ocean Floor” “sinks” below the continent(s) and provides the habitats of marine organisms


Continental Drift

  • If we know the Continental Crust and Oceanic Crust have different densities…how did they “separate” to become 7 continents and 4 oceans?

  • We start (Pangea) 210 mya!


PANGEA (the super continent)

  • 180 million yrs. ago – all continents were attached together and have slowly moved apart over time

  • Discovered (S. F. Bacon, 1600’s) “Coasts of continents fit together like a puzzle.”

  • Lead to theory of continental drift and plate techtonics.


Pangea (reptile fossils)


  • So…WHERE DID WE START AND WHERE ARE WE NOW?


Figure 2.14a


Figure 2.14e


PLATE TECTONICS

  • Continental drift leads to the theory of Plate tectonics

  • Although Bacon discussed it in the 1600’s, it was not understood until the 1960’s.


The Ocean Floor (P. Tectonics)

  • Mid-Ocean Ridges

    • Underwater mountain ranges

    • Fault: Crack in earths crust

    • Rift: Ocean crust separates & creates “cracks”

    • Earthquakes are common

  • Trenches

    • Deep depressions in the seafloor

    • Mostly in Pacific, Volcanoes common


Major features of Sea Floor


CO 2

Mid-Atlantic Ridge (above sea surface in Iceland)


Sea-Floor Spreading (plate tectonics)

  • New sea-floor forms at mid-ocean ridges (where the edge of these “plates” meet)

  • Continental Drift: If the plate (as it spreads away from the ridge) contains continental crust (on top) the continents “drift” (move) apart.


How? Convection and Density!


Figure 2.08

Sea Floor Spreading:

X-section of sea floor @

Mid ocean ridge


Figure 2.07

Paleomagnetism:

Normal magnetism

@ ridge crests (but

Reversed in other

locations)


We get:

  • Plate boundaries

  • With geologic activity, such as earthquakes, that (may) correspond w/ these plate boundaries


Earthquake and Volcano distribution


Lithospheric plate boundaries


How does everything move? Plate Tectonics!

  • The earth’s upper layer, the lithosphere, is divided into plates

  • Plates may contain sea-floor, continents, or both

  • Plates are moving (few cm per year), floating on top of the earth’s molten mantle


Subduction (plate techtonics)

  • sea-floor is destroyed by plunging back into the earth’s interior at trenches

  • When 2 plates collide, 1 dips below the other (in to the mantle) and 1 is destroyed (causing, sometimes, earthquakes)

  • Ocean vs. Cont. plate: ocean plate destroyed, can get coastal mountain ranges

  • Ocean vs. Ocean plate: 1 dips = volcano or earthquake

  • Cont. vs. cont: none destroyed, mnt. Ranges fold

  • 2 plates, no collision, lock/shear/earthquake (S. Andreas F)


Figure 2.10

Continental + Oceanic plate collision = trench, earthquake


Figure 2.11

2 oceanic plates collide = trench/earthquake


San

Andreas

Fault

(CA)

Figure 2.13


Sea Floor Regions

  • All of this “plate” movement and geologic activity that occurs under the water yields different sea floor regions

  • Each dependent upon depth, width, slope etc.


Regions of the sea-floor

  • Continental Margins contain continental shelf, slope and rise

  • Cont. shelf = shallow, most “rich” (diverse)

  • Deep Ocean Floor, “Abyssal Plain”

  • The Ocean “floor” (on average) is 2-3.5 miles BELOW the oceans (water) surface!


Figure 2.17

Continental margin


Active vs. Passive Margins

An active margin

is a geologically

very “active” area;

whereas a

Passive margin is a

geologically

in-active

area.


(Passive Margin) Continental Shelf (19 mi. off of Atlantic City, NJ)

Figure 2.18

Tom’s Canyon

Shelf break


The California Coast

Monterey

Canyon


Active Coast (CA)


Margins

  • We know what it looks like at the top of the (Continental) margin but what does it look like AT the margin (at the ridge line, deep under the oceans surface)?


“Black

Smoker”

Hydro-

thermal

Vent

(at a

Mid

Ocean

Ridge)

Figure 2.24


Black Smoker, cross section


Who are we?

  • Iceland, Azores = fault (mountain)

  • Andes (mts.) = subduction trench (o-c)

  • Aleutian/Mariana (Is.) = sub. trench (o-o)

  • Himalayas (mts.) = sub. Trench (c-c)

  • Hydrothermal vents: Deep Ocean

  • See Fig. 2.5 for locations and other “interesting” places to visit.


Major features of Sea Floor


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