ELEMENTS OF OCEANOGRAPHY

 

TOPIC 8 - DENSITY AND TEMPERATURE IN THE WORLD'S OCEANS [Lecture ppt | pdf]

Overheads:

Sources of Heat to the Ocean
As with the atmosphere, the major source of heat for the oceans is solar insolation
Most solar insolation arrives at the ocean surface (uppermost 100 m) in the Tropics
Other regionally important heat sources are volcanic eruptions, general heat flow and hot spring near mid-ocean ridges, and anthropogenic effects (waste or cooling water discharges)

Heat Budget for the Oceans
Heat added to the oceans must be balanced by heat loss from the oceans. There are three major ways for the oceans to lose heat
­ Back radiaton of long-wavelength (infrared) radiation from warm ocean surfaces
­ Advection of heat by direct einteraction with winds at the ocean/atmosphere interface
­ Evaporation of water (latent heat of vaporization)

Temperature Variations in the World's Oceans
Warmest water occurs in the surface Tropical oceans
Coldest water occurs at the poles
Heating in mid-latitudes (summer only) and Tropical (always) causes mixing of surface ocean to depths of several hundred meters
Sharp temperature drop below the mixed layer is called the thermocline

Seawater Density
Average seawater density is 1.025 gr/cc
Water density is sensitive to variations in temperature and salinity
Water is densest near 4 degrees C at low salinity
Oceanographers talk about seawater density in terms of oT, where
oT= (water density- 1) x 1000

Density Variations in the World's Oceans
The oceans are somewhat stratified with warmer and less dense water at the surface and colder, denser water at depth
As seawater freezes, it excludes salts and makes the remaining seawater even more saline. Sea ice is less dense than surrounding seawater and floats
As evaporation occurs, the remaining seawater also becomes more saline
As a water mass changes density, it will sink or rise until it joins other water with similar density

Water Masses and Water Types
Temperature (T) and salinity (S) combine to produce volumes of water with specific water characteristics
A water mass has a characteristic range of T, S; a water type has a single value of T, S
Formation of water masses is fundamental part of ocean circulation. Areas of water mass formation change T, S and the resulting water mass moves to balance changes. This global circulation pattern is called thermohaline circulation

Some Important Water Masses in the World's Oceans
North Atlantic Deep Water (NADW) is a cold, high-salinity water mass left after formation of ice in Arctic. It sinks and flows southward in the Atlantic
Antarctic Bottom Water (AABW) is a cold, very high- salinity water mass formed in the Antarctic. It sinks and flows northward into the Atlantic, Pacific, and Indian Oceans
Mediterranean Intermediate Water (MIW) is a warm, high-salinity water mass formed in the Mediterranean Sea. It flows into into the Atlantic and becomes an intermediate water mass

 

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