Ocean Basins Chapter 15 PDF

Chapter 15 Ocean Basins Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  The Origin of Oceans Where did water come from? Native volatiles from the molten early Earth Gases from...

Chapter 15 Ocean Basins Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  The Origin of Oceans Where did water come from? Native volatiles from the molten early Earth Gases from initial coalescence Cometary water The moon-forming impact would have caused net loss of volatiles Why do volcanoes still spew water vapor? ▶ Volatiles recycled with tectonic activity Early solar system was full of comets Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.1 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.2 Comet Hale–Bopp, shown here in 1997, was probably the most widely observed comet of the twentieth century. Valerio Pardi/Shutterstock.com Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  The Earth’s Oceans Crustal differences Oceanic crust is denser than continental crust Rides lower – isostatically Thinner – 4 to 7 kilometers (km) versus 20 to 40 for continental crust Ocean basins cover 71% of Earth 2 to 11 km in depth (approximately 5 km average) 1.4 billion km3 water No basins, water would be 2 km deep everywhere Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.3 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Studying the Sea Floor Sampling Rock dredge – open-mouth steel net Coring – a pipe is used to collect a mud core Sea-floor drilling – like as used for oil drilling Submersibles – both manned and robotic Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.4 Source: Adapted from http://c2fn.dt.insu.cnrs.fr/spip/IMG/jpg/carottier_kullenberg_et_schema.jpg Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Studying the Sea Floor Remote sensing Echo sounding – used to map seafloor topography (SONAR) Seismic profiler – like sonar, but higher-energy waves penetrate sea-floor and reflect data back Magnetometer – towed behind ships to record magnetic fields of rock Microwave radar – used to map sea-surface, surface mimics sea-floor topography Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.10 Source: http://walrus.wr.usgs.gov/mapping/csmp/images/seismic_multichannel.jpg Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (1 of 6) Mid-ocean ridges After World War One – early echo-sounding technology showed topography After World War Two – more detailed maps made for naval use Mid-Ocean Ridge system – continuous mountain chain connected across the globe, about 80,000km long Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.13 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (2 of 6) Rift valley – 1 to 2 km wide split along the ridge’s center where new crust forms Normal faults and earthquakes in valley Transform faults – hundreds of fractures crossing perpendicular to the ridge Black-smokers – sulfur-laden jets of hot water occurring near ridges Chemosynthesis – bacteria produce hydrogen sulfide in the black-smokers Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.14 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.15 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.16 Seawater is heated as it circulates through the hot rocks of the rift zone, and it dissolves metals and sulfur from the rocks. The ions precipitate as “smoke,” consisting of tiny mineral grains, when the hot suspension spews into cold ocean water. OAR/National Undersea Research Program (NURP); NOAA Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (3 of 6) Global sea-level change Continent and basin ratios affect sea-level Tectonics can cause continents to move, shift, come together, and become relatively higher or lower Spreading rates affect sea-level Fast spreading causes a higher seafloor Higher seafloor means less volume for water Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.19 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (4 of 6) Oceanic trenches and island arcs Trench – narrow, often deep, depression along a subduction zone (8 to11 km) Marianas trench Island arc – form above the subducting plate boundary Accreted terrane – when a plate with an island arc subducts and causes the arc to become part of the continental crust Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.20 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.21 NASA-JSC Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (5 of 6) Explain why the Mid-Oceanic Ridge is topographically elevated above the surrounding ocean floor. Why does its elevation gradually decrease away from the ridge axis? Explain the origin of the rift valley in the center of the Mid-Oceanic Ridge. Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.22 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Features of the Seafloor (6 of 6) Seamounts, oceanic islands, and atolls Seamount – submarine mountain that rises 1km above sea floor Oceanic island – a seamount that rises above the ocean surface Hawaiian Island chain Guyot – a worn down, sunken, oceanic island Atoll – circular coral reef surrounding a central lagoon Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.25 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.26 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.27 Tahiti Tourist Board Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.28 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Sediments and Rocks of the Sea Floor (1 of 2) Early thought was that old oceans would have thick sediments everywhere Discovered in 1947 that mud was thinner closer to ridges Ocean floor sediments Terrigenous sediment – sand, silt, clay eroded and transported from continents Pelagic sediments – mix of fine clays and biogenic debris Abyssal plain – flat expanses of pelagic sediments Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Sediments and Rocks of the Sea Floor (2 of 2) Basaltic ocean crust Pillow basalt – rounded basalt structure caused by magma oozing out into the cool ocean 1 to 2km thick Vertical basalt dikes 3 to 5km thick Gabbro Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.29 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.30 © Integrated Ocean Drilling Program Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.31 © oar/national undersea research program Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Continental Margins (1 of 4) Passive continental – continental and oceanic crust joined Continental shelf – shallow, gently sloping surface. Sediment laden – isostatically depressed Carbonate platforms – limestone beds, occur in warm areas with little sediment Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.33 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.34 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.36 Clear skies and calm waters allowed the MODIS satellite to capture this stunning image of southern Florida, the Bahamas, and Cuba. In the center, Andros Island is surrounded by the bright blue halo of the Great Bahama Bank, a carbonate platform that was inundated by a rising sea level between 10,000 and 2,500 years ago as the last ice-age glaciers were melting. In most places, the water above the platform doesn’t exceed 6 meters. Liam Gumley, Space Science and Engineering Center, University of Wisconsin-Madison Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Continental Margins Continental slope – steep edge of the shelf where oceanic and continental crust meet Continental rise – slope shallows out and meets the deep ocean floor Submarine canyon – deep valley eroded into the continental shelf Abyssal fan – sediment fan often found at end of submarine canyon Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Continental Margins (2 of 4) Continental slope – steep edge of the shelf where oceanic and continental crust meet Continental rise – slope shallows out and meets the deep ocean floor Submarine canyon – deep valley eroded into the continental shelf Abyssal fan – sediment fan often found at end of submarine canyon Turbidity currents – form when loose, wet sediments tumble downslope A rapid and extensive submarine landslide Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Continental Margins (3 of 4) Active continental margins – forms at subduction zones Once plate (oceanic) is actively descending beneath the other (continental) Trench associated with descending slab 4 degrees to 5 degrees near top, steepens to 15 degrees or more at depth Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  Continental Margins (4 of 4) Explain how a continental shelf–slope–rise complex forms on a continental margin. Why does an active continental margin typically have a steeper continental slope than a passive margin? Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.  FIGURE 15.38 Earth Science: An Introduction, Third Edition. Hendrix/Thompson/Turk. @2021 Cengage Learning, inc.