35
Descriptive Oceanography
from pack ice and can extend to 70 m above sea level (as much as 500 m long). The volume
below sea level varies from 1:1 to 7:1 depending on its shape. The drift of icebergs is influenced by water currents, while pack ice is influenced by winds. The pack ice moves to the
right in the Northern Hemisphere because of the Coriolis force. This was known by sailors
long before it was noted by Nansen or suggested by Ekman.
1.4.6 Closed basins
1.4.6.1 Mediterranean Sea
The Mediterranean Sea is divided into a western and eastern basin separated by a sill of
400 m that extends from Sicily to North Africa. The maximum depths are 3400 m in the
western basin and 4200 m in the eastern basin. The sill depth between the Mediterranean
and the Atlantic is 330 m. The Mediterranean Sea is an example of a closed basin that has
a higher rate of evaporation than the rate of precipitation and an input of river water. This
results in high salinities (S = 39) being formed in the surface layers. These waters sink
in the winter and form saline deep waters. Off the coast of Turkey, lavantine intermediate waters are formed with a temperature of 15°C and salinity of 39.1. These waters flow
toward the west at 200 to 600 m and out through the Strait of Gibraltar into the Atlantic.
The Mediterranean water that flows into the Atlantic has a temperature of 13°C and salinity of 37.3 from mixing with the incoming Atlantic waters. The deep and bottom waters
are formed during the winter off the Riviera in the western basin (t = 12.6°C and S = 38.4)
and in the South Adriatic Sea in the eastern basin (t = 13.3°C and S = 38.65). Since the deep
waters are replenished, they have high concentrations of oxygen.
1.4.6.2 Red Sea
The average depth of the Red Sea is 1000 m, with a maximum depth of 2200 m. The sea is
separated from the Indian Ocean by a sill of 100 m depth. Because of the very dry climate,
evaporation exceeds precipitation by about 200 cm yr –1 . There is no river runoff into the
Red Sea. This leads to salinities as high as 42.5, combined with temperatures of 30°C in
the summer and 18°C in the winter. The deep water below the sill depth has a uniform
temperature and salinity (t = 21.7°C and S = 40.6). This water is formed in the winter
in the north. The intermediate water that flows out over the sill starts with a temperature of 25°C and salinity of 39.8 and becomes 15°C and 36 salinity outside the sill. This
subsurface flow is compensated by a surface inflow of Indian Ocean water. This is similar
to the Mediterranean Sea. The Red Sea water that flows over the sill can be identified in the
northern Indian Ocean. In the northern Red Sea, hot brine pools were discovered in some
deep trenches. Temperatures of 58°C and salinities of 320 have been found. The compositions of the solutions indicate that the brines were formed by hot seawaters dissolving
evaporite deposits.
1.4.6.3 Estuaries
Conditions in coastal waters of the ocean are quite different in many ways from those
in the open oceans. Variations with location and time are generally larger. These differences are caused by river runoff, tidal currents, and the effects of coastal boundaries on
circulation. Tidal currents twice a day change the volume of water in a harbor or bay and
promote vertical mixing. This breaks down any stratification in the water and can cause
Descriptive Oceanography
from pack ice and can extend to 70 m above sea level (as much as 500 m long). The volume
below sea level varies from 1:1 to 7:1 depending on its shape. The drift of icebergs is influenced by water currents, while pack ice is influenced by winds. The pack ice moves to the
right in the Northern Hemisphere because of the Coriolis force. This was known by sailors
long before it was noted by Nansen or suggested by Ekman.
1.4.6 Closed basins
1.4.6.1 Mediterranean Sea
The Mediterranean Sea is divided into a western and eastern basin separated by a sill of
400 m that extends from Sicily to North Africa. The maximum depths are 3400 m in the
western basin and 4200 m in the eastern basin. The sill depth between the Mediterranean
and the Atlantic is 330 m. The Mediterranean Sea is an example of a closed basin that has
a higher rate of evaporation than the rate of precipitation and an input of river water. This
results in high salinities (S = 39) being formed in the surface layers. These waters sink
in the winter and form saline deep waters. Off the coast of Turkey, lavantine intermediate waters are formed with a temperature of 15°C and salinity of 39.1. These waters flow
toward the west at 200 to 600 m and out through the Strait of Gibraltar into the Atlantic.
The Mediterranean water that flows into the Atlantic has a temperature of 13°C and salinity of 37.3 from mixing with the incoming Atlantic waters. The deep and bottom waters
are formed during the winter off the Riviera in the western basin (t = 12.6°C and S = 38.4)
and in the South Adriatic Sea in the eastern basin (t = 13.3°C and S = 38.65). Since the deep
waters are replenished, they have high concentrations of oxygen.
1.4.6.2 Red Sea
The average depth of the Red Sea is 1000 m, with a maximum depth of 2200 m. The sea is
separated from the Indian Ocean by a sill of 100 m depth. Because of the very dry climate,
evaporation exceeds precipitation by about 200 cm yr –1 . There is no river runoff into the
Red Sea. This leads to salinities as high as 42.5, combined with temperatures of 30°C in
the summer and 18°C in the winter. The deep water below the sill depth has a uniform
temperature and salinity (t = 21.7°C and S = 40.6). This water is formed in the winter
in the north. The intermediate water that flows out over the sill starts with a temperature of 25°C and salinity of 39.8 and becomes 15°C and 36 salinity outside the sill. This
subsurface flow is compensated by a surface inflow of Indian Ocean water. This is similar
to the Mediterranean Sea. The Red Sea water that flows over the sill can be identified in the
northern Indian Ocean. In the northern Red Sea, hot brine pools were discovered in some
deep trenches. Temperatures of 58°C and salinities of 320 have been found. The compositions of the solutions indicate that the brines were formed by hot seawaters dissolving
evaporite deposits.
1.4.6.3 Estuaries
Conditions in coastal waters of the ocean are quite different in many ways from those
in the open oceans. Variations with location and time are generally larger. These differences are caused by river runoff, tidal currents, and the effects of coastal boundaries on
circulation. Tidal currents twice a day change the volume of water in a harbor or bay and
promote vertical mixing. This breaks down any stratification in the water and can cause