Geoscience Reference
In-Depth Information
(a
) Paci
c (180°)
(b) Atlantic (40°W)
0
288
294
284
288
282
500
278
1000
1500
276
278
2000
276
2500
3000
3500
4000
4500
5000
5500
60°
S
40°
S
20°
S
Equator 20°
N
40°
N
60°
N
60°
S
40°
S
20°
S
Equator 20°
N
40°
N
60°
N
Figure 2.17 Vertical cross sections of temperature for (a) the Pacific Ocean along the
International Date Line and (b) the Atlantic Ocean at 30°W. Contour interval is 2 K,
and depth is in m.
Note the following in
Figure 2.17:
• The warmest waters, as you would expect, are located at the surface in the
tropics.
• Between 40°S and 40°N, the isotherms are aligned horizontally, denoting
the stable layering of the oceans at these latitudes, with warmer (less dense)
water floating on top of cold water.
• Isotherms at high latitudes in the Southern Hemisphere, and high latitudes
in the North Atlantic (but not in the North Pacific), are oriented vertically. In
these regions, surface waters are as cold as the deep ocean water, just a few
degrees above the freezing point of fresh water (273.15 K). This orientation
of the isotherms at high latitudes provides clues about the large-scale
circulation of the oceans, discussed in
chapter 9.
Three layers are defined for the ocean. The
ocean mixed layer
(or simply
“the mixed layer”) is characterized by strong interactions with the atmosphere.
Surface winds induce robust vertical mixing and horizontal currents in this
region. As a consequence of this stirring of the ocean by the atmosphere, tem-
perature is not a strong function of depth in the mixed layer. Depending on
season and latitude, the mixed layer is 20-200 m deep and contains roughly
2% of the volume of the ocean. The permanent
thermocline
(or
pycnocline
) is
