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