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Chapter 15
Earth’s Oceans
The Global Ocean
• One vast body of water covering more than two thirds of Earth’s surface
• Oceans contain 97% of the water on Earth• Oceanographers study the oceans:– Water chemistry– Wave action– Marine organisms– Sediments
Data Collection
• Surface– Sonar—find the depth of the ocean, map
undersea mountain ranges– Floats and Satellites (TOPEX/Poseidon)—map
temperature, salinity, wave motion• Deep water—unmanned and manned
submersibles (Alvin)• Computers—model information about tides,
tsunamis, pollution, climate change
Research Ships
Sentry and Alvin HMS Challenger
Origin of the Oceans
• Oceans have existed almost since the beginning of Earth’s geologic history.
• Evidence indicates that the source of the water on Earth was– volcanic eruptions (water vapor)– impacts with comets and meteorites
Distribution of Earth’s Water
• The southern hemisphere has much more water than the northern hemisphere.
Sea level changes (due to melting glaciers and thermal expansion)
Major Oceans
• Pacific• Atlantic• Indian• Arctic• Southern
Chemical Composition of Seawater
• Water• NaCl• MgCl2
• KCl• CaCl2
• Average salt concentration is 3.5% (varies from 3.2% to 3.7%)
• Salt added and removed is in equilibrium
Ocean Stratification (Layering)
• Ocean water forms layers based on density, caused by temperature and salinity differences
Water Masses
• AABW: Antarctic Bottom Water—coldest and most dense
• NADW: North Atlantic Deep Water—less dense than AABW
Ocean Movements: Waves
Waves
• Shallow water causes waves to slow down
Ocean Movements: Tides
• Tides are caused by gravitational effect of both the Moon and the Sun
• Spring Tides: higher tidal range
• Neap tides: lower tidal ranges
Ocean Movements: Currents
• Gyres (horizontal surface currents) transfer heat from equator to poles
Ocean Movements: Currents
• Density currents (ocean conveyor belt) move vertically as well as horizontally
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