Geoscience Reference
In-Depth Information
located between 200 and 800 m depth, depending on the geographic location.
It is stably stratified, with temperature decreasing and density increasing with
depth. The deep ocean, which extends to the bottom below the permanent
thermocline, contains 80% of the ocean's water. Here, temperature decreases
slowly with depth.
Additional insight about the thermal structure of the upper layers in the
tropics results from taking east-west cross sections through the Atlantic (50°W
to 10°E) and Pacific (130°E to 80°W) Oceans along the equator. The mixed
layer and the upper thermocline are represented in
Figure 2.18
.
• The mixed layer in the west in both basins is relatively deep, or well
developed, with warm water extending to 100 m depth or more. (Note
the weak stratification in this region denoted by the wide spacing of the
isotherms.)
• The depth of the mixed layer decreases to the east, and the thermocline tilts
upward and brings cooler water to the surface in the eastern ocean basins.
This structure is consistent with
Figure 2.15,
which indicates that sea surface
temperatures in the western parts of these basins are significantly warmer
than in the east.
• Below about 250 m depth, the isotherms are lat.
Salinity
is related to the mass of dissolved salts in 1 kg of seawater. Most of
the dissolved salts contain sodium and chloride ions, but magnesium, sulfur,
calcium, and potassium ions are also present. Salinity values can be written in
terms of grams of salt per kilogram of water (g/kg), or parts per thousand (ppt).
(a
) Paci
c
0
296
292
100
288
300
300
296
296
288
292
292
200
288
288
300
284
284
284
284
130°E
150°E
170°E
170°W
150°W
130°W
110°W
90°W
(b
) Atlantic
0
300
300
292
100
296
292
288
200
288
284
300
284
284
50°W
40°W
30°W
20°W
10°W
0°
10°E
Figure 2.18 Cross sections of annual mean ocean temperature (K) in the upper 400 m
of the ocean along the equator for (a) the Pacific (130°E to 80°W) and (b) the Atlantic
(50°W to 10°E) Ocean basins. White areas are continents.
