The Oceans

Composition

The Oceans

• There are five main oceans:– Pacific, Atlantic, Indian, Arctic, Antarctic

The Oceans

The oceans contain 97 percent of the water found on Earth.

The remaining 3 percent is freshwater located in: •frozen ice caps • rivers and lakes•underground sources

Source of Earth’s Water

Comets

Shortly after the formation of Earth, violent volcanism released huge amounts of water vapor and other gases.

As the planet cooled, the water vapor condensed into oceans.

Distribution of Earth’s Water

Approximately 71 percent of Earth’s surface is covered by oceans that have an average depth of 3800 m.

Northern hemisphere: oceans

only cover 61 percent of the surface.

Southern hemisphere: water covers 81 percent.

Salinity

The Composition of Seawater

Salinity is the total amount of solid material dissolved in water.

oceanographers typically express salinity in parts per thousands: 35 ppt (or 3.5 percent)

Most of the salt in seawater is sodium chloride, common table salt.

Salinity

The Composition of Seawater

Sources of Sea Salt• Chemical weathering of rocks on the continents

is one source of elements found in seawater.

• The second major source of elements found in seawater is from Earth’s interior.

Salts in Seawater

Salinity Processes Affecting Salinity

The Composition of Seawater

• Processes that decrease salinity:

• Processes that increase salinity:

- Precipitation

- Runoff from land - Icebergs melting- Sea ice melting

- Evaporation- Formation of sea ice

Natural Processes Affecting Salinity

Ocean Temperature Variation The ocean’s surface water temperature

varies with the amount of solar radiation received, which is primarily a function of latitude.

The Composition of Seawater

• Thermocline: layer of ocean water between about 300 - 1000 meters where there is a rapid change of temperature with depth.

Temperature Variation with Depth

• The thermocline is a very important structure because it creates a barrier to marine life.

Variations in Ocean Surface Temperature

Variations in Ocean Water Temperature

Ocean Density Variation

Density = Mass / Volume

The Composition of Seawater

• Seawater density is influenced by two main factors: salinity and temperature.

Factors Affecting Seawater Density

Ocean Density Variation

The Composition of Seawater

Ocean Zones

Primary Productivity Productivity in Polar Oceans

Oceanic Productivity

• The low availability of solar energy limits photosynthetic productivity in polar areas.

Productivity in Tropical Oceans• Productivity in tropical regions is limited by the

lack of nutrients.

Water Layers in the Tropics

Productivity in Northern Hemisphere, Temperate Oceans

Food Chains and Webs