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