Chapter 15: Ocean Basins
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Chapter 15: Ocean Basins. Tubeworms, tiny crabs and other sea life use heat, minerals and chemical energy near hot water vents on the deep sea floor to survive without sunlight.

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Fig. 15-1, p.354


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The Earth’s Oceans planets, which eventually formed our atmosphere, oceans and foundation for life on Earth.

  • Oceans cover about 71% of the Earth’s surface. The seafloor is about 5 km deep in the central part of ocean basins. Oceans basins are continually changing. What is happening with the Pacific and the Atlantic ocean basins? (one is closing while the other is enlarging)…Why does water eventually end up in the oceans? (read on the density of oceanic crust, Page 377).

  • Oceans affect global climate and the biosphere in many ways:

    • They reflect and store solar heat different than rocks/soil (oceans are generally warmer in the winter and cooler in the summer than adjacent land).

    • Most precipitation is from evaporation from oceans.

    • Ocean currents transport heat toward poles.

    • Plate tectonics alters basins which alters currents and affect climate.


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Fig. 15-2, p.354


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Fig. 15-3, p.355


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Fig. 15-4, p.356


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Fig. 15-5, p.357


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Fig. 15-6a, p.357 sounder. A sound wave bounces from the sea floor and back up to the ship, where its travel time is recorded.


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Fig. 15-6b, p.357


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Fig. 15-7, p.358


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  • The Mid-Oceanic Ridge System (MORS) and other features of the sea floor show there is as much topography here as on the continents. MORS is a continuous submarine mountain chain that encircles the globe; it rises 2-3 km above the sea floor, and is Earth’s largest mtn chain (covering 20% of its surface).


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Fig. 15-7b, p.358


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Fig. 15-8, p.360


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Fig. 15-9, p.360


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Fig. 15-10, p.361


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  • The MORS can cause a rise and fall in global sea level (if they didn’t exist, sea level would fall 400 meters). Slow spreading (above) creates a narrow, low-volume ridge that displaces less sea water and lowers SL.

  • Rapid sea floor spreading (right) creates high-volume ridge, displacing more sea water and raises SL.

Fig. 15-11, p.361


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  • Life on the Mid-Oceanic Ridge. they didn’t exist, sea level would fall 400 meters). Slow spreading (above) creates a narrow, low-volume ridge that displaces less sea water and lowers SL.

  • Black smoker to right (see page 384).

Fig. 15-12, p.362


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Fig. 15-13, p.362 they didn’t exist, sea level would fall 400 meters). Slow spreading (above) creates a narrow, low-volume ridge that displaces less sea water and lowers SL.


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Fig. 15-14, p.362


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Fig. 15-16, p.363


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Fig. 15-16a, p.363 becomes part of it (to buoyant to sink). This is a way continents can grow by accreted terranes.


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Fig. 15-16b, p.363 becomes part of it (to buoyant to sink). This is a way continents can grow by accreted terranes.


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Fig. 15-16c, p.363 becomes part of it (to buoyant to sink). This is a way continents can grow by accreted terranes.


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Fig. 15-17, p.364


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Seamounts, Oceanic Islands and Atolls micro-continents and island arcs from the Pacific Ocean that were added to the continent.

  • Seamount: submarine mtn that rises 1 km or more above the ocean floor.

  • Oceanic Island: is a seamount that rises above sea level.

    -both are volcanoes commonly made of basalt formed at a “hot spot” above a mantle plume. As the plate overrides the hot spot, the seamount becomes inactive. The Hawaiian Island-Emperor Seamount Chain is an example (15.18). As the seamounts move away they erode into a flat-topped “guyot” and sink.


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Fig. 15-18, p.365


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Fig. 15-19, p.365


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Fig. 15-20, p.366


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Fig. 15-20a, p.366 away from the mantle plume.


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Fig. 15-20b, p.365 away from the mantle plume.


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Fig. 15-22a, p.367 island. As the island sinks, the reef continues to grow upward to form a barrier reef that encircles the island. Finally, the island sinks below sea level and the reef forms a circular atoll.


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Fig. 15-22b, p.367 island. As the island sinks, the reef continues to grow upward to form a barrier reef that encircles the island. Finally, the island sinks below sea level and the reef forms a circular atoll.


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Fig. 15-22c, p.367 island. As the island sinks, the reef continues to grow upward to form a barrier reef that encircles the island. Finally, the island sinks below sea level and the reef forms a circular atoll.


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Fig. 15-21, p.366


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  • Sediments and rocks of the sea floor. described in Figure 15.22. Over time, storm waves wash coral sands on top of the reef and vegetation grows on the sand.

  • The three layers of oceanic crust are layer 1: sediment (Terrigenous and Pelagic); layer 2: pillow basalt and layer 3: upper mantle (basalt dikes and gabbro).

  • The oceanic crust is 4-7 km thick (1-2 km of pillow basalts and 3-5 km of dikes/gabbro).

Fig. 15-23, p.368


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  • Terrigenous sediment is sand, silt and clay eroded from the continents and carried to the deep sea floor by gravity (rivers, landslides) and submarine currents.

  • Pelagic sediment collects even on the deep sea floor far from continents (clay and remains of tiny plants and animals). It accumulates at a rate of 2-10 mm/1000 yrs. Near the MOR there is virtually none (why?).

Fig. 15-24, p.368


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Fig. 15-25, p.368


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  • Continental margins. continents and carried to the deep sea floor by gravity (rivers, landslides) and submarine currents.

Fig. 15-26, p.370


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Fig. 15-26a, p.370


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Fig. 15-26b, p.370


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Fig. 15-26c, p.370


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  • A passive continental margin consists of a broad continental shelf, slope and rise formed by the accumulation of sediment eroded from the continent.

  • Submarine canyons are deep valleys from the edge of a continent to the rise (where abyssal fans may form) and occur where large rivers enter the sea. Sediments from rivers create turbidity currents that can travel as speed greater than 100 km/hr for up to 700 km.

Fig. 15-27, p.371


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Fig. 15-28, p.371 shelf, slope and rise formed by the accumulation of sediment eroded from the continent.


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Fig. 15-29, p.372


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p.374 beneath a continent, forming an oceanic trench. The continental shelf is narrow, the slope is steep and no rise exists.


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