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Chapter 12 – THE OCEANS
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The Oceans Ocean basins No geologic record of time before water
Origin of water on Earth is debated 1st proposal = water originated inside Earth 2nd proposal = water arrived from outer space via meteorite impacts
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The Oceans Ocean basins Earth has 4 huge water basins
Pacific Ocean Atlantic Ocean Indian Ocean Southern Ocean *Arctic Ocean Cover 71% of Earth’s surface
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The Oceans Composition of seawater Salinity
Measure of salt content of solution Seawater salinity ranges % Elements in seawater come from: Chemical weathering of rock Volcanic eruptions & black smokers Evaporation of surface water (increases salinity) Freezing of seawater (increases salinity)
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The Oceans Layers in the ocean
3 major layers in oceans in which density differs: Surface layer ( 2%; warmest) Thermocline (18%; just above freezing point) Deep Zone (80%; temperature low & constant)
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The Oceans Ocean currents Surface currents Christopher Columbus
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The Oceans Ocean currents
Deep currents: “Great Ocean Conveyor Belt” (thermohaline circulation) North Atlantic Deep Water Antarctic Bottom Water Gulf Stream
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The Oceans How oceans regulate climate
Oceans moderate coastal climates Continental interiors = more extreme Conveyor belt re-distributes heat from tropics to poles Elimination of conveyer belt (e.g., Gulf Stream) could cause ice age
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Where the Ocean Meets Land
Changes in sea level Global volume change Barely noticeable in human lifetime Account for great change in position of shore line over geologic time Global warming = sea level rise Current global warming = 2.4 mm/year rise Global cooling = sea level drop
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Where the Ocean Meets Land
Changes in sea level Tides Regular daily cycle of rise & fall of sea level resulting from gravitational action of Moon, Sun, & Earth
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Where the Ocean Meets Land
Changes in sea level Tides Run-up height Tidal range Spring tide Neap tide Tidal bore
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Where Ocean Meets Land Changes in sea level (continued) Waves
Ocean waves receive energy from wind Surf “Broken”, turbulent water found between line of breakers &shore Rip currents Wave refraction
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Where Ocean Meets Land Changes in sea level continued
Erosion & transport of sediment by waves Longshore current Current in surf zone; flows parallel to coast Beach drift Particles driven up/down beach slope by wave action
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Where the Ocean Meets Land
3 kinds of shorelines & coastal landforms Rocky coasts Wave-cut cliff Coastal cliff cut by wave action at base of rocky coast Wave-cut bench Marine terrace
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Where the Ocean Meets Land
3 kinds of shorelines & coastal landforms Beach Wave washed sediment along coast
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Where Ocean Meets Land Kinds of shorelines & coastal landforms
Barrier Island Long, narrow, sandy island offshore & parallel to low land coast Spit Lagoon
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Where Ocean Meets Land Kinds of shorelines & coastal landforms Tombolo
Bay barrier Estuary Estuary
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Where Ocean Meets Land Kinds of shorelines & coastal landforms Reefs
Hard structure on shallow ocean floor, built by coral Polyps- tiny coral animals that deposit calcium carbonate Fringing reef Barrier reef Atoll Highly productive ecosystems
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Coastal Processes & Problems Lab
Active continental margin Located near plate boundaries Narrow continental shelf & coastal plain I.e. Pacific coast Passive continental margin Not located near plate boundaries Wider continental shelf & coastal plain I.e. Gulf coast; Atlantic coast
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Coastal Processes & Problems Lab
Waves Crest Trough Wave height (crest – trough) Wavelength (crest to crest) Wave period (time it takes 2 crests to pass fixed point) Factors that affect waves Wind speed Wind duration Fetch
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Coastal Processes & Problems Lab
Coastal erosion & deposition Headlands = erosion (energy concentrated) Bays = deposition (energy dispersed) Wetland erosion Wetlands = barriers for storm surge & large waves Mississippi River delta wetlands being eroded due to human actions River modifications
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Coastal Processes & Problems Lab
Human modification of coastlines Groins Jetties Breakwaters Seawalls Problems
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Coastal Processes & Problems Lab
Hurricane ingredients Atmospheric disturbance Warm ocean water Light upper atmospheric winds Hurricane damage Storm surge High winds Rainfall & flooding Tornadoes
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