Properties of Seawater

What are the three basic physical properties of seawater?

Temperature, salinity and density.

How are the properties of seawater interrelated?

Temperature influences density. For pure water, density increases as the temperature decreases. Salinity influences this relationship in that the saltier the water, the denser it becomes. Furthermore, salinity lowers the freezing point to below 0°C (32°F).

What two factors determine seawater temperature?

Latitude and depth.

How does latitude affect seawater temperature?

The sun heats the atmosphere unevenly and heats the oceans unevenly as well. Ocean temperatures vary with latitude from just below freezing at the poles to about 25v27°C (77v80.6°F) at the equator.

How does depth affect seawater temperature?

Sunlight does not penetrate deep into the ocean, so temperature varies with depth. In low latitudes, ocean temperature is constant down to about 200 m, and then decreases abruptly over the next 800 m until it reaches a steady value below 1,000 m.

Thermocline

A zone of rapid temperature change between the warm surface waters and the cooler deep waters

Seasonal thermocline

The 200-m transition boundary is the seasonal thermocline, and its exact depth varies seasonally.

Permanent thermocline

The 1,000-m transition boundary.

Polar thermocline

The polar latitudes have no thermoclines because deep and shallow waters are well mixed.

What two factors affect salinity?

Latitude and depth.

How does latitude affect seawater salinity?

The salinity of seawater is determined by how much freshwater enters the ocean in the form of precipitation, melting sea ice, and runoff from rivers, and how much exits through evaporation. Salinity is higher in the temperate and tropical areas where evaporation rates are higher than in polar regions.

How does depth affect seawater salinity?

Salinity also varies with depth. The amount of variation depends on location. In some locations salinity decreases with depth, while in others it increases with depth.

Halocline

A zone in which there is a rapid vertical change in salinity .

What two factors affect seawater density?

Latitude and depth.

How does latitude and depth affect seawater density?

The temperature and salinity of seawater influence its density. Temperature and salinity vary with latitude. Therefore, the density of seawater also varies with latitude.

How does depth affect seawater density?

Density varies with depth. In the lower latitudes (temperate and tropical regions), density is steady to about 200 m, increases to a depth of 1,000 m, and then remains steady below 1,000 m.

Pycnocline

The zone of rapid vertical change in density due to changes in temperature and salinity.

Why are the depths of Pycnoclines, Haloclines, and Thermoclines similar?

For the most part, the depths of pycnoclines correspond to those of haloclines and thermoclines because temperature, salinity, and density are related.

Why does density not change with depth in polar regions?

The mixing of deep and shallow waters.

What are the three layers of seawater?

Surface mixed zone, Transition zone and Deep zone.

Surface mixed zone

(0-200 m deep) Warmest, least dense, low salinity; 2% of the world's seawater.

Transition zone

(200-1000 m deep) Colder, saltier and denser; 18% of the world's seawater.

Deep zone

(Greater than 1000 m deep) Coldest, saltiest, densest; 80% of the world's seawater.

Do the polar zones have a layered structure?

No. This layered structure doesn't exist in polar regions where deep and shallow waters are well mixed.

What possible affects for circulation of water around the globe does changes in density have?

Prevailing winds and the Coriolis effect create surface currents in the oceans. As waters move around the world, they change temperature and density. When this happens, they rise or sink depending on the nature of the change.

Global Thermohaline Circulation

Deep-sea currents that occur because of differences between the salinity and temperature characteristics of water masses.

What is the Global Thermohaline Circulation also called?

Global conveyor belt.

Describe the "global conveyor belt" circulation pattern.

In this circulation pattern, cold, dense, saline-rich water sinks in the North Atlantic Ocean and deep water rises in the Pacific and Indian oceans. The global conveyor belt mixes the waters of the world's oceans slowly over time.

How do temperature, salinity and density affect the transmission of sound waves in seawater?

Sound travels faster through liquids than it does through air. Temperature, salinity, and density all affect the speed at which sound travels in seawater. The velocity of sound through seawater therefore varies with depth.

Transmission of sound waves in the surface zone of seawater.

(0-150 m) well-mixed waters where velocity increases mainly due to increased pressure (pressure is affected by density).

Transmission of sound waves in the thermocline of seawater.

(150v1,000 m): waters where sound velocity decreases due to decreasing temperatures.

Transmission of sound waves in the deep zone of seawater.

(below 1,000 m): waters where sound velocity increases due to increased pressure and relatively constant temperature.

What happens to sound waves traveling through multiple layers of seawater?

Just as sound waves from SONAR reflect off the seafloor, sound waves can reflect between layers of different densities in the ocean.

Because seawater absorbs light, how far can light penetrate seawater?

About 200 meters.

Do all wavelengths of light (colors) penetrate seawater the same?

No. Red light gets absorbed first, followed by orange and ultraviolet, and then yellow. After about 50 m, the only colors remaining are blue and blue-green.

What is the affect of light wavelengths (colors) being absorbed at different depths?

The result is that the color of an object you would see underwater would depend upon the depth.

What color is the ocean below 200 meters and why?

Below 200 m, the ocean is black because no light from the surface reaches these depths.

What affects the visibility of objects in seawater?

The visibility of objects in seawater also depends on how many particles are suspended in the water. For example, visibility is limited in Atlantic coastal waters due to high sediment content. In the warm tropical waters of the Caribbean, however, visibility is excellent.