Geoscience Reference
In-Depth Information
1.0
36
0.5
Salinity
34
0
-0.5
32
-1.0
E-P
30
90°S
60°S
30°S
Equator
30°N
60°N
90°N
Figure 2.20 Zonally averaged sea surface salinity (gray line) calculated
for all oceans and the difference between evaporation and precipitation
(E − P; black line).
evaporates from the ocean, the salt left behind increases surface salinity. Sub-
tropical waters are relatively salty because E > P in this region. Near the equator,
in the ITCZ, P > E and the surface waters are freshened. The relationship breaks
down at high latitudes. In the Arctic, surface waters are freshened by outflow
from numerous rivers. The high salinity of the Antarctic circumpolar region is a
result of sea ice formation, which leaves salt behind in the ocean.
Figure 2.21 shows the vertical and meridional structure of salinity in the
Atlantic and Pacific Ocean basins. Highest salinity values do not occur at the
surface, but near the base of the ocean mixed layer. The high salinity of the sub-
tropical Atlantic Ocean, especially in the Northern Hemisphere, is displayed
clearly in the figure. The salinity of polar surface waters is relatively low, and
the vertical alignment of the contours at high latitudes is similar to that of the
isotherms in Figure 2.17.
Ocean currents are analogous to wind in the atmosphere for portraying
circulation. Figure 2.22 is a schematic representation of ocean surface current
directions.
Western boundary currents flow along the western edges of each ocean
basin. Examples are the Gulf Stream, the Kuroshio, the Agulhas Current, and
the Brazil Current. These are warm currents, so called because they carry
relatively warm water from lower latitudes to higher latitudes.
Eastern boundary currents flow along the eastern edges of each ocean basin.
Examples are the California, Peru, and Benguela Currents. These are cold
currents that low from high latitudes to low latitudes in both hemispheres.
• Boundary currents are stronger and more well developed in the Northern
Hemisphere, because the continents in that hemisphere enclose the ocean
basins more completely.
• The North and South Equatorial Currents straddle the equator and low
from east to west. The Equatorial Countercurrent lies in between, and it
brings water back eastward below the surface.
 
 
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