© 2011 Pearson Education, Inc. Ocean Basins

What does the bottom of the ocean look like? Can anything live down there? Is the middle of the ocean the deepest part? © 2011 Pearson Education, Inc.

Answer: Over a century and a half ago, most scientists believed that the ocean floor was completely flat and carpeted with a thick layer of muddy sediment containing little of scientific interest. Further, it was believed that the deepest parts were somewhere in the middle of the ocean basins. However, as more and more vessels crisscrossed the seas to map the ocean floor and to lay transoceanic cables, scientists found the terrain of the sea floor was highly varied and included deep troughs, ancient volcanoes, submarine canyons, and great mountain chains. It was unlike anything on land and, as it turns out, some of the deepest parts of the oceans are actually very close to land! (Trujillo, 2010) © 2011 Pearson Education, Inc.

Bathymetry Measures the vertical distance from the ocean surface to mountains, valleys, plains, and other sea floor features Echo Soundings –Echo sounder - reflection of sound signals

© 2011 Pearson Education, Inc. Echo Sounding Record

© 2011 Pearson Education, Inc. Measuring Bathymetry Modern Acoustic Instruments Side scan sonar Towed behind ship. Provides detailed bathymetric map.

© 2011 Pearson Education, Inc.

Side Scanning Sonar

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Sea Floor Mapping from Space Satellites measure sea floor features based on gravity

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Ocean Areas Three Major Areas Continental areas –Shallow areas close to shore Deep-ocean basins –Deep areas farther from land Mid-ocean ridge –underwater mountain range

Continental Areas Non-Active –Not close to plate boundaries –No major tectonic activity –Example: East coast of Canada Active –Associated with convergent or transform plate boundaries –Much tectonic activity

Passive and Active Continental Margins

© 2011 Pearson Education, Inc. Continental Area Features Continental shelf Continental slope Continental rise

© 2011 Pearson Education, Inc. Continental Area Features

© 2011 Pearson Education, Inc. Ocean Trenches and Volcanic Arcs Convergent tectonic plates create ocean trenches. –Deepest part of oceans –Deepest – Mariana Trench at 11,022 meters (36,161 feet) Volcanic arc on non subducted ocean plate –May produce island arc, Japan

Figure 3.14

© 2011 Pearson Education, Inc. Mid-Ocean Ridge

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Mid-Ocean Ridge Features SeamountPillow lava

© 2011 Pearson Education, Inc. Mid-ocean Ridge Features Hydrothermal Vents Sea floor hot springs Create ecosystems able to survive without sunlight

© 2011 Pearson Education, Inc. Hydrothermal Vents