Chapter 15

Ocean Water and Ocean Life

Section 15.1

The Composition of Seawater

The Composition of Seawater

Salinity – is the total amount of solid material dissolved in water. • Because the proportion of dissolved

substances in seawater is such a small number, oceanographers typically express salinity in parts per thousands.

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

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.

• Volcanic eruptions emitted water vapor and elements – chlorine, bromine, sulfur and boron.

Salts in Seawater

The proportion of dissolved substances in seawater is usually expressed in

A. Parts per hundred.B. Parts per thousand.C. Parts per ten thousand.D. Parts per million.

Which of the following is a source of dissolved substances in the ocean?

A. Chemical weathering of rocksB. Evaporation of water from the seas and

oceanC. Excretions from marine organismsD. Melting icebergs and sea ice

The Composition of Seawater

Salinity• Processes Affecting Salinity

– Processes that decrease salinity:• Precipitation• Sea ice melting• Icebergs melting• Runoff from land

The Composition of Seawater

Salinity• Processes Affecting Salinity

– Processes that increase salinity:• Evaporation• Formation of sea ice

Natural Processes Affecting Salinity

Which does NOT decrease salinity?

A. PrecipitationB. RunoffC. EvaporationD. Ice melting

The Composition of Seawater

Ocean Temperature Variation• The ocean’s surface water temperature varies

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

• Temperature Variation with Depth– The thermocline is the layer of ocean water

between about 300 meters and 1000 meters where there is a rapid change of temperature with depth.

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

Variations in Ocean Surface Temperature

Variations in OceanWater Temperature

The Composition of Seawater

Ocean Density Variation• Density is defined as mass per unit

volume. It can be thought of as a measure of how heavy something is for its size.

• Factors Affecting Seawater Density– Seawater density is influenced by two main

factors: salinity and temperature.

The Composition of Seawater

Ocean Density Variation• Density Variation with Depth

– The pycnocline is the layer of ocean water between about 300 meters and 1000 meters where there is a rapid change of density with depth.

Variation in Ocean Water Density

Differing amounts of solar radiation across Earth’s latitude affect the

ocean’s

A. Salinity in the thermocline.B. Density at the surface.C. Temperature at the surface.D. Density in the thermocline.

Which of the following occurs when the ocean’s salinity increases?

A. Density increasesB. Density decreasesC. Temperature increasesD. Temperatures decreases

Which of the following occurs when temperature decreases?

A. Density decreasesB. Density increasesC. Salinity increasesD. Nothing happens

The layer of ocean water between 300 meters and 1000 meters where there is a rapid change in density.

A. ThermoclineB. Transition zoneC. PycnoclineD. Deep zone

The Composition of Seawater

Ocean Layering• Oceanographers generally recognize a three-

layered structure in most parts of the open ocean: a shallow surface mixed zone, a transition zone, and a deep zone.

• Does not exist in high latitudes because there is no rapid change in temp or density.1. Surface Zone

• Shallow (300 to 450 meters)• Zone of mixing• Sun-warmed zone

The Composition of Seawater

Ocean Layering

2. Transition Zone– Between surface layer and deep zone– Thermocline and pycnocline

3. Deep Zone– Sunlight never reaches this zone.– Temperatures are just a few degrees above

freezing. – Constant high-density water

Ocean Zones

Which of these is NOT one of the three layers of the ocean?

A. Photic zoneB. Surface zoneC. Transition zoneD. Deep zone

Where would you not find this three-layered structure of the open ocean?

A. High latitudesB. Low latitudesC. Deep ocean zoneD. Intertidal zone