§ chapter 15: ocean basins. § tubeworms, tiny crabs and other sea life use heat, minerals and...

§ Chapter 15: Ocean BasinsChapter 15: Ocean Basins

§ Tubeworms, tiny crabs and other sea life use Tubeworms, tiny crabs and other sea life use

heat, minerals and chemical energy near hot heat, minerals and chemical energy near hot water vents on the deep sea floor to survive water vents on the deep sea floor to survive without sunlight.without sunlight.

§

§ ““Bolide” impacts Bolide” impacts may have brought may have brought volatiles to the inner volatiles to the inner planets, which planets, which eventually formed eventually formed our atmosphere, our atmosphere, oceans and oceans and foundation for life foundation for life on Earth.on Earth.

§ See page 376 for an See page 376 for an explanation of this explanation of this drawing.drawing.

Fig. 15-1, p.354

The Earth’s OceansThe Earth’s Oceans

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

§ Oceans affect global climate and the biosphere in many ways:Oceans affect global climate and the biosphere in many ways:§ They reflect and store solar heat different than rocks/soil (oceans are They reflect and store solar heat different than rocks/soil (oceans are

generally warmer in the winter and cooler in the summer than generally warmer in the winter and cooler in the summer than adjacent land).adjacent land).

§ Most precipitation is from evaporation from oceans.Most precipitation is from evaporation from oceans.§ Ocean currents transport heat toward poles.Ocean currents transport heat toward poles.§ Plate tectonics alters basins which alters currents and affect climate.Plate tectonics alters basins which alters currents and affect climate.

§ Halley’s Comet. The early Solar System was crowded Halley’s Comet. The early Solar System was crowded with comets, meteoroids and asteroids. Bolide impacts with comets, meteoroids and asteroids. Bolide impacts may have imported volatiles such as CO2, water vapor, may have imported volatiles such as CO2, water vapor, ammonia, simple organic molecules and other volatiles.ammonia, simple organic molecules and other volatiles.

Fig. 15-2, p.354

§ Schematic cross section of the continents and ocean Schematic cross section of the continents and ocean basins. Vertical axis shows elevation relative to sea basins. Vertical axis shows elevation relative to sea level. Horizontal axis shows the relative areas of the level. Horizontal axis shows the relative areas of the types of topography (e.g., mountains and ocean floor).types of topography (e.g., mountains and ocean floor).

Fig. 15-3, p.355

§ Studying the seafloor: Oceanographers Studying the seafloor: Oceanographers extract sediment from a core retrieved extract sediment from a core retrieved from the seafloor.from the seafloor.

Fig. 15-4, p.356

§ Alvin is a Alvin is a research research submarine submarine capable of capable of diving to the diving to the sea floor. sea floor. Scientists on Scientists on board control board control robot arms robot arms to collect to collect sea-floor sea-floor rocks and rocks and sediments.sediments.

Fig. 15-5, p.357

§ Mapping the topography of the sea floor with an Mapping the topography of the sea floor with an echo sounder. A sound wave bounces from the echo sounder. A sound wave bounces from the sea floor and back up to the ship, where its sea floor and back up to the ship, where its travel time is recorded.travel time is recorded.

Fig. 15-6a, p.357

§ A seismic A seismic profiler records profiler records both the sea both the sea floor topography floor topography and the layering and the layering of sea floor of sea floor sediments and sediments and rocks.rocks.

Fig. 15-6b, p.357

§ Features of the Features of the Sea FloorSea Floor

Fig. 15-7, p.358

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

§ Divergent plate boundaries, or spreading Divergent plate boundaries, or spreading centers, coincide exactly with the MORS in the centers, coincide exactly with the MORS in the world’s oceans.world’s oceans.

Fig. 15-7b, p.358

§ The sea floor sinks as it grows older. At the MORS, new The sea floor sinks as it grows older. At the MORS, new lithosphere is buoyant because it is hot and of low lithosphere is buoyant because it is hot and of low density. It ages, cools, thickens and becomes denser density. It ages, cools, thickens and becomes denser as it moves away from the ridge and sinks. The central as it moves away from the ridge and sinks. The central part of the sea floor lies at a depth of about 5 km.part of the sea floor lies at a depth of about 5 km.

Fig. 15-8, p.360

§ A cross-section A cross-section view of the view of the central rift valley central rift valley of the MORS. As of the MORS. As the plates the plates separate, blocks separate, blocks of rock drop of rock drop down along the down along the fractures to form fractures to form the rift valley. the rift valley. The moving The moving blocks cause blocks cause earthquakes earthquakes along “normal” along “normal” faults. faults.

Fig. 15-9, p.360

§ Transform faults offset segments of the MOR. Transform faults offset segments of the MOR. Adjacent segments of the ridge may be Adjacent segments of the ridge may be separated by steep cliffs 3 km high. Note the separated by steep cliffs 3 km high. Note the flat abyssal plain far from the ridge. flat abyssal plain far from the ridge.

Fig. 15-10, p.361

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

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

Fig. 15-11, p.361

§ Life on Life on the Mid-the Mid-Oceanic Oceanic Ridge. Ridge.

§ Black Black smoker smoker to right to right (see page (see page 384).384).

Fig. 15-12, p.362

Fig. 15-13, p.362

§ Oceanic Oceanic Trenches and Trenches and Island Arcs: An Island Arcs: An oceanic trench oceanic trench forms at a forms at a convergent convergent boundary boundary between two between two oceanic plates. oceanic plates. One plate sinks, One plate sinks, generating generating magma that magma that rises to form a rises to form a chain of chain of volcanic islands volcanic islands called an island called an island arc.arc.

Fig. 15-14, p.362

§ Onekotan is one of many volcanic islands in the Kuril Onekotan is one of many volcanic islands in the Kuril Island arc that formed along the Kuril trench in the Island arc that formed along the Kuril trench in the western Pacific. The deepest place on Earth is the western Pacific. The deepest place on Earth is the Mariana trench of the sw Pacific, where the ocean floor Mariana trench of the sw Pacific, where the ocean floor sinks to about 11 km below SL.sinks to about 11 km below SL.

§ Island arcs Island arcs eventually migrate eventually migrate toward a continent toward a continent and becomes part and becomes part of it (to buoyant to of it (to buoyant to sink). This is a way sink). This is a way continents can continents can grow by accreted grow by accreted terranes. terranes.

Fig. 15-16, p.363

Fig. 15-16a, p.363

Fig. 15-16b, p.363

Fig. 15-16c, p.363

§ The The accreted accreted terranes of terranes of western western North North America are America are micro-micro-continents continents and island and island arcs from arcs from the Pacific the Pacific Ocean that Ocean that were added were added to the to the continent. continent.

Fig. 15-17, p.364

Seamounts, Oceanic Islands and AtollsSeamounts, Oceanic Islands and Atolls

§ SeamountSeamount: submarine mtn that rises 1 : submarine mtn that rises 1 km or more above the ocean floor. km or more above the ocean floor.

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

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

§ The Hawaiian The Hawaiian Island-Emperor Island-Emperor Seamount Chain Seamount Chain becomes older becomes older in a direction in a direction going away from going away from the island of the island of Hawaii. In 10-15 Hawaii. In 10-15 million years the million years the island of Hawaii island of Hawaii may sink and may sink and become eroded.become eroded.

Fig. 15-18, p.365

§ The Hawaiian Islands and Emperor Seamounts The Hawaiian Islands and Emperor Seamounts sink as they move away from the mantle sink as they move away from the mantle plume.plume.

Fig. 15-19, p.365

§ Formation of a guyot.Formation of a guyot.

Fig. 15-20, p.366

Fig. 15-20a, p.366

Fig. 15-20b, p.365

§ A fringing reef grows along the shore of a young A fringing reef grows along the shore of a young volcanic island. As the island sinks, the reef volcanic island. As the island sinks, the reef continues to grow upward to form a barrier reef continues to grow upward to form a barrier reef that encircles the island. Finally, the island sinks that encircles the island. Finally, the island sinks below sea level and the reef forms a circular below sea level and the reef forms a circular atoll.atoll.

Fig. 15-22a, p.367

Fig. 15-22b, p.367

Fig. 15-22c, p.367

§ The Tetiaroa Atoll in French Polynesia formed The Tetiaroa Atoll in French Polynesia formed by the process described in Figure 15.22. Over by the process described in Figure 15.22. Over time, storm waves wash coral sands on top of time, storm waves wash coral sands on top of the reef and vegetation grows on the sand. the reef and vegetation grows on the sand.

Fig. 15-21, p.366

§ Sediments and rocks of the Sediments and rocks of the sea floor.sea floor.

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

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

Fig. 15-23, p.368

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

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

Fig. 15-24, p.368

§ Pillow lavas…how do they form?Pillow lavas…how do they form?Fig. 15-25, p.368

§ Continental Continental margins.margins.

Fig. 15-26, p.370

§ Continental crust fractured as Pangea began to Continental crust fractured as Pangea began to rift. rift.

Fig. 15-26a, p.370

§ Faulting and erosion thinned the crust as it Faulting and erosion thinned the crust as it separated. Rising basaltic magma formed new separated. Rising basaltic magma formed new oceanic crust in the rift zone. oceanic crust in the rift zone.

Fig. 15-26b, p.370

§ Sediment eroded from the continents formed Sediment eroded from the continents formed broad continental shelves on the passive broad continental shelves on the passive margins of North America and Africa. margins of North America and Africa.

Fig. 15-26c, p.370

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

§ Submarine canyons are deep valleys from the edge of a continent Submarine canyons are deep valleys from the edge of a continent to the rise (where abyssal fans may form) and occur where large to the rise (where abyssal fans may form) and occur where large rivers enter the sea. Sediments from rivers create turbidity rivers enter the sea. Sediments from rivers create turbidity currents that can travel as speed greater than 100 km/hr for up to currents that can travel as speed greater than 100 km/hr for up to 700 km. 700 km. Fig. 15-27, p.371

Fig. 15-28, p.371

§ At an active continental margin an oceanic At an active continental margin an oceanic plate sinks beneath a continent, forming an plate sinks beneath a continent, forming an oceanic trench. The continental shelf is narrow, oceanic trench. The continental shelf is narrow, the slope is steep and no rise exists. the slope is steep and no rise exists.

Fig. 15-29, p.372

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