CHAPTER 6
STRUCTURE OF THE OCEANS
Objectives
1.
2.
3.
4.
To understand the role that the oceans play in the thermal or heat budget of our planet.
To build a picture of the structural (spatial and temporal) consequences of these density interactions (controlled
by temperature and salinity), that allow us to measure and delineate the internal, layered structure of the world’s
oceans, and explain much of the deep horizontal and vertical oceanic circulation.
To understand how we can decipher the complex internal structure of the oceans with relatively simple
measurements of temperature and salinity.
Finally, if the oceans are driven as a part of the surface heat engine of the atmosphere and hydrosphere, then an
enormous energy resource waits to be tapped. We will look at some of the best proposed ways to tap this energy.
Key Concepts
Major Concept (I)
The earth receives solar radiation unequally over its surface; with the intensity
per unit area of surface greatest at the equator, intermediate in the middle
latitudes, and the lowest intensity is at the polar regions.
Related or supporting concepts:
- If the earth had no atmosphere, and sunlight struck its surface at exactly 90°, radiation would bombard
the surface at a theoretical value (input rate) of 2 calories per square centimeter per minute
(cal/cm2/min). This value is called the solar constant.
- The sun is so far away, its rays of light can be considered nearly parallel when they reach earth.
- On our real earth, the sun’s rays can strike the earth’s surface at right angles only between 23.5°N
(Tropic of Cancer) and 23.5°S (Tropic of Capricorn).
- Other areas of the earth’s surface receive much less solar energy per unit area per unit time since the
earth’s surface is curved.
- The earth’s atmosphere reduces the maximum theoretical amount of solar radiation that can reach
earth’s surface from 2 cal/cm2/min to approximately 1.6 cal/cm2/min. This is because the atmosphere
both absorbs and reflects solar radiation.
- Therefore, the earth’s surface is heated unequally.
Major Concept (II)
The earth must lose an amount of heat back to space that is equal to the amount
it gains from the sun or else the earth’s average temperature, about 16°C,
would increase or decrease with time.
Related or supporting concepts:
- The earth’s heat budget is illustrated in figure 6.2.
- If assume 100 units of incoming solar energy reach the earth's outer atmosphere, 35 units will be
reflected to space immediately (31 from the upper atmosphere and 4 from the surface of the earth).
The remaining 65 units are absorbed by earth’s surface and atmosphere.
- Of the 65 units of heat absorbed, 47.5 are absorbed by the earth's surface and the remaining 17.5 are
absorbed by the atmosphere.
- To maintain a heat balance, the earth must reradiate 65 units of heat back to space. This is
accomplished by the loss of 59.5 units of heat from the atmosphere and 5.5 units from the earth’s
surface.
- Notice that in the above calculations the surface of the earth has absorbed 47.5 units of heat and lost
only 5.5 units for a net gain of 42 units of heat. At the same time the atmosphere absorbs 17.5 units of
heat while losing 59.5 units of heat for a net loss of 42 units of heat.
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The lost 42 units of heat from the atmospheric are replaced by the 42 units of heat gained by the earth’s
surface. This transfer is accomplished by evaporation, conduction, and reradiation.
To understand the heat budget of a portion of the ocean, we need to know the following:
a. the total energy absorbed,
b. the loss of energy due to evaporation,
c. the transfer of heat (advectively) through currents (input and outflow of energy),
d. warming or cooling of the overlying atmosphere due to energy at the sea surface, and
e. heat reradiated to space from the sea surface.
Major Concept (III) The intensity of solar radiation available at the earth’s surface varies not only with
latitude, but with the time of year (see fig. 6.5).
Related or supporting concepts:
- The intensity of solar radiation at middle latitudes between about 40° and 60°N & S is highly
variable annually. This is because the angle of the sun’s rays reaching the surface is highly variable at
these latitudes.
- The intensity of solar radiation is fairly constant through the year in the tropics.
- Polar latitudes are subject to severe changes in length of daylight.
- Land and ocean respond very differently to the annual changes in solar radiation.
- Land has low heat capacity, it gains or loses heat over a short period of time (such as overnight!), while
the oceans have a very high heat capacity, absorbing or releasing heat with very small changes in
temperature. (Think about maritime vs continental climates.)
- The average annual range in sea surface temperatures is quite small because of water’s high heat
capacity and the transfer of heat through the water by mixing. Sea surface temperature variations range
from:
a. 0° to 2°C in the tropics,
b. 5° to 8°C at middle latitudes, to
c. 2° to 4°C at polar latitudes.
Major Concept (IV) The salinity of mid-ocean surface waters is controlled by global patterns of precipitation
and evaporation. Higher salinities are found where surface waters evaporate
the most, while lower salinities are found where rainfall is abundant.
Related or supporting concepts:
- The average ocean salinity is about 35 ppt.
- Sea surface salinities in the tropics are a relatively low 34.5 ppt due to high rainfall which dilutes the
surface water.
- Salinity reaches its highest values of about 36.7 ppt near 30° North and South where there is little
precipitation and evaporation strips water from the sea surface and concentrates the salts.
- The salinity drops again to about 34 ppt at higher latitudes between 50° and 60° North and South where
annual precipitation is again high and low average temperatures reduce the rate of evaporation.
- At polar latitudes the salinity of the water varies annually. In the winter the formation of sea ice
concentrates the salt and increases the salinity. In the summer the melting ice reduces the salinity.
Major Concept (V)
The basic controls on the density of water masses in the world’s oceans are
temperature and salinity. It is critical to remember that many combinations of
temperature and salinity can create the same density (see fig. 6.8).
Related or supporting concepts:
- Less dense water masses remain at the ocean’s surface, while more dense waters tend to sink to an
equilibrium level. These simple physical reactions, coupled with wind, tidal, and wave generated
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forces, means that the density of the ocean waters changes with depth, latitude, and proximity to coastal
regions in a fairly predictable (and observable) manner.
The surface 100 m (330 ft) of the world’s oceans is well-mixed, and therefore homogeneous in
its density.
Layers of increasing density occur at depths from 100–1000 m (330–3300 ft). The plot of density with
depth reveals a rapid change until about 1000 m (330 ft), with deeper waters of very similar or slowly
increasing density. The sharp break in the slope of the plot is termed the pycnocline.
Temperature also decreases rather rapidly with depth below the 100 m (330 ft) level to the 1000 m
(3300 ft) depth. The zone where the temperature changes most rapidly with depth is called the
thermocline. Similar in behavior to density, below 1000 m (3300 ft), the temperature of the oceans is
relatively uniform, with gradual decreases down to the bottom.
As with temperature and density, salinity increases rapidly from 100–1000 m (330–3300 ft), then
remains nearly uniform below 1000 m (3300 ft). The zone where the most rapid changes in salinity
with depth occur is called the halocline (halo- for halite, the mineral name for common table salt).
A water column where the density of the water increases with depth is said to be stable. If the density
decreases with depth the water column is unstable and will generally lead to overturn and mixing of the
water column. A water column with no changes in density, temperature, or salinity can therefore be
called isopycnal, isothermal, and isohaline, respectively.
In the open ocean seasonal temperature changes are more important than changes in salinity in
controlling density.
Near continental margins variations in salinity become more important in controlling density because of
freshwater runoff. Very cold freshwater runoff at high latitudes can have such a low density that it will
not sink. Instead it will remain at the surface as a freshwater lid.
Major Concept (VI) Any process that creates an unstable water column (i.e., variations in temperature or
salinity) will generate vertical circulation in the water as it attempts to regain
stability or equilibrium. This vertical circulation is important in the mixing and
exchange of energy and other components in the ocean. We call this
thermohaline circulation.
Related or supporting concepts:
- Minute changes in density are responsible for generating extremely large-scale vertical motions of
water masses or changes in the rates of their circulation.
- Because changes in the density of seawater are generally very small, physical oceanographers choose to
deal with a representation of density called sigma-t. Sigma-t is calculated by first dividing the density
value by the density of pure water (1.0 g/cm3) to cancel the units. You then subtract 1.0 from the result
and multiply by 1000. Sigma-t is a dimensionless number.
- To make their life easier, they commonly only deal with the density differences in the thousands of
g/cm3, for example, a density of 1.02677 converts easily to a sigma-t of 26.77.
- Oceanographers typically measure density to five decimal places!
Major Concept (VII) Dense water sinking in the oceans reaches an equilibrium depth and is then driven
horizontally by the continued sinking of dense water behind it. Water at the
surface moves into the zone of sinking, while at some other point in the ocean,
water must rise to replace it (see fig. 6.13).
Related or supporting concepts:
- Areas where water masses move downward are called downwelling zones, and conversely, areas where
water rises are called upwelling zones.
- There is approximately a constant volume of water in the oceans so whenever currents remove water
from one location it must be replaced from another location. This idea is called continuity of flow.
- Downwelling brings oxygenated waters to the depths, while upwelling can bring needed nutrients and
decomposition products to surface waters.
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Wind-driven surface currents can generate upwelling or downwelling zones in various ways. Wind
blowing offshore creates upwelling in coastal regions. Where surface currents and winds converge,
downwelling can occur. Where surface winds and wind-driven currents diverge, upwelling can occur
in the open ocean.
Rates of upwelling and downwelling are slower than oceanic surface (wind-driven) currents with rates
of 0.1-1.5 m/day compared to 1.5 m/sec. This is important, as it means that 1000s of years are required
for upwelling or downwelling processes to complete a cycle of overturn in the deep ocean.
The velocity of horizontal flow on the deep sea floor is only about 0.01 cm/sec.
The motion of water masses through the oceans can be mapped using chemical tracers. These tracers
change their distribution with time as currents flow and are often components added to the oceans by
human actions. A good example would be radioactive isotopes introduced into the environment by
nuclear testing in the late 1950s and early 1960s.
Major Concept (VIII)
Water masses in the oceans can be identified and tracked using chemical
tracers.
Related or supporting concepts:
- Chemical tracers are typically present in seawater at low concentrations. They have no effect on water
motion.
- The concentration of chemical tracers changes with time.
- Tracers have usually been added to the oceans by human actions.
- A variety of radioactive chemical tracers were added to the oceans as a result of the atmospheric testing
of nuclear weapons in the 1950s and 1960s. These tracers still persist in the water and can be used to
monitor water motion over long periods of time.
- The Geochemical Ocean Sections (GEOSECS) program, conducted in 1972–73, used these radioactive
tracers to determine that surface water containing these tracers had reached the seafloor at a depth of
5000 m (16,400 ft) in the Atlantic north of 40˚N. South of this latitude no radioactive substances were
found below a depth of 3000 m (10,000 ft). These results indicated a faster rate of downwelling than
was predicted.
- The Transit Tracers in the Ocean (TTO) experiment in 1981 found radioactive material that had
descended to the sea floor as far south as 30˚N. South of this the North Atlantic was free of radioactive
material at depths below 2000 m (6500 ft).
- Current work on water movement revealed by radioactive tracers is focussing on tritium, a radioactive
isotope of hydrogen that is found in some water molecules.
- Tritium has a half-life of 12.45 years. It decays to an inert form of helium.
- Tritium is most effective in studies that involve age calculations less than ten years and in shallow
waters where there is the least amount of naturally occurring helium.
Major Concept (IX) The world’s oceans have been studied carefully in terms of their salinity, temperature,
and density, so that we can map the layered structure of the world’s oceans (fig.
6.14).
Related or supporting concepts:
- All the world’s oceans have layered characteristics and distinct water types.
- These water types, or masses, obtain their characteristic physical properties (density, salinity,
temperature) at the surface of the oceans.
- The density of a water mass will determine the depth to which it sinks.
- Depth zones are often defined as: surface, 0–200 m (0–650 ft); intermediate, 300–2000 m (1000–6500
ft); deep, 2000–4000 m (6500–13,000 ft); and bottom, depths below 4000 m (13,000 ft).
- The volume of water in a water mass, and hence its thickness and horizontal extent, are determined by
the rate of its formation and the area over which it is forming.
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For this summary we will concentrate on the Atlantic layers or water types (fig. 6.14):
a. North Atlantic Deep Water (NADW): Waters of a salinity of 34.9 ppt, and temperature of 2–
4°C sink as the waters of the Norwegian Sea, Labrador Current, and cooler Gulf Stream
converge and move southward.
b. Antarctic Intermediate Water (AAIW): Waters converge at 40°S with a temperature of 5°C
and 34.4 ppt salinity it rides just above the deep water.
c. Antarctic Bottom Water (AABW): Waters generated along the edge of Antarctica are very
cold (-0.5°C), salty (34.8 ppt), and are the densest waters created in the oceans. These waters
creep northward along the bottom, wedging below the North Atlantic Deep Water.
d. South Atlantic Surface Water (SASW): This water type is formed where North Atlantic Deep
Water is forced to the surface in the area near 60°S, splits, and part of it moves northward.
e. Mediterranean Intemediate Water (MIW): The temperature of this water is 13°C and it is very
salty (37.3 ppt). MIW exits the Straits of Gibraltar, mixes somewhat with Atlantic waters, and
drops to a depth of about 1000 m (3300 ft) as it moves out into the Atlantic. This unique
water mass is traceable some 2500 km (1500 mi) from the Straits of Gibraltar.
The Atlantic Ocean is relatively narrow and confined, so that water types and masses are more readily
definable and traceable than in most of the other oceans, and have been studied the most extensively.
Specific water types can be created in bodering seas and then enter ocean basins. One example has
already been discussed, Meditrranean Intermediate Water. A second example is water from the
Red Sea.
Red Sea water with a salinity of 40–41 ppt enters the Indian Ocean and spreads out at a depth of 3000
m (10,000 ft) more than 200 km (124 mi) south of its source.
Temperature and salinity profiles for the world’s oceans are shown in fig. 16.18a-f in your book.
There is relatively little internal mixing between water masses. Horizontal mixing tends to be more
important than vertical mixing because whenever a water mass is displaced vertically by turbulence,
buoyancy forces return it to its original depth.
Major Concept (X)
Temperature and salinity can be plotted for each water mass via a temperature
versus salinity graph, thereby defining distinct T-S curves for each geographical
region in the world’s oceans.
Related or supporting concepts:
- T-S curves for geographically related areas of the oceans are similar, and fall into groups or families we
call water masses.
- A water mass with only one temperature value and one salinity value over its entire extent is called a
water type. (For example, Antarctic Bottom Water is a water type.)
- Some organisms have become specifically adapted to very narrow ranges of temperature and salinity-therefore, some can act as biological indicators of water masses or even water types.
Major Concept (XI) The information gained by examining the ocean waters in such detail for temperature
and salinity is so valuable that techniques for measuring these properties have
been used and perfected for well over a hundred years.
Related or supporting concepts:
- A wide variety of seawater characteristics are studied by oceanographers who go to sea aboard
sophisticated research vessels that serve as platforms for launching diverse sampling and measuring
instruments.
- Reseach time at sea is very expensive and, for a large vessel, can total as much as $25,000 per day for
the ship and crew alone. The expenses associated with the research team and their equipment is added
to these basic operating expenses.
- Oceanography during the first half of this century depended on robust mechanical sampling and
measuring devices that were lowered from the surface on cables. They descended to a pre-determined
depth, took a sample or made a measurement, and they were brought back to the surface for analysis.
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One example of such a device is a mechanical water bottle like the one shown in fig. 6.21. Water can
be sampled in bulk from any depth in the oceans using remotely controlled closing bottles, lowered on
thin steel cable or hydrowire, sometimes with spring-loaded closing devices at each end of the bottle
(actually a hollow cylinder with gaskets). The ends of the bottle are then closed or tripped by weights
(messengers) dropped down the wire when the bottle is at the precise depth. Signals for opening and
closing can now be transmitted electronically to more sophisticated bottles.
While oceanographers still use bottom corers, grabs, dredges, and nets, the use of water bottles with
attached thermometers is decreasing.
Direct-reading instruments are available that transmit data on conductivity, temperature, and depth
continuously down into the sea and are (surprised?) called CTD’s (see fig. 6.22 in your text).
CTDs provide a depth profile of salinity by measuring the conductivity and temperture of the water.
Conductivity is a function of salinity and temperature so the temperature has to be measured to obtain
accurate salinity values for a given conductivity.
CTD systems still require a ship to stop and remain on station while they are lowered and recovered.
A modified CTD called Seasoar allows sampling while a vessel is under way (see fig. 6.23). It can be
towed at depths that range from the surface to about 350 m (1100 ft).
Major Concept (XII) Large amounts of solar energy are stored in the oceans.
Related or supporting concepts:
- The transparency and heat capacity of water allow it to store large amounts of heat energy.
- This heat can be extracted independent of daily and seasonal changes in the intensity of solar
radiation.
- Systems designed to extract this heat are called ocean thermal energy conversion (OTEC)
systems (see fig. 6.24).
- OTEC systems depend on the difference in temperature between ocean surface water and
water at a depth of 600–1000 m (2000–3300 ft).
- Presently there are two OTEC designs, a closed cycle and an open cycle system.
- In the closed system warm surface water is passed over an evaporator chamber filled with
Freon or ammonia which is vaporized by the relatively warm temperature of the water. The
vapor builds up pressure in a closed chamber that can be released to turn a turbine which then
generates power. After passing through the turbine the gas is then sent to condenser where it
is cooled by cold water pumped up from depth. Once in liquid form the Freon or ammonia is
then returned to the evaporator to complete the cycle.
- In the open system large amounts of seawater are converted to steam in a low-pressure
vacuum chamber and the steam is used as the working substance in place of Freon or
ammonia. Passing the steam through the condenser creates desalinated water.
- Either system can be located onshore, offshore, or on a ship that would be free to move from
place to place.
- OTEC requires at least a 20˚C difference in temperature between surface and deep water to
generate useful amounts of energy. This means that these plants would have to be located at
latitudes between 25˚N and 25˚S where surface water is appreciably warmer than deep water.
- Estimates indicate that about 0.07% of the solar energy absorbed by tropical surface water
could be extracted with OTEC systems. While this is a small percentage, it still represents a
large amount of energy.
- OTEC systems have the potential to change the local ecosystem. Pumping cold, deep water to
the surface will also transfer nutrients that are more highly concentrated at these depths to the
surface. This could alter the surface productivity.
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Matching Key Terms with Major Concepts
At the end of the chapter in the textbook is a list of key terms. You should be able to match each of these with one of
the previously listed major concepts. To test your ability, try to match the following key terms with the number (I–
XII) of the appropriate major concept identified in this section:
solar constant
water type
downwelling
isopycnal
water mass
chemical tracers
upwelling
heat budget
T-S curves
sigma-t
CTD
divergence
thermocline
hydrocast
convergence
tritium
Test Your Recall
Answer the following questions to test your understanding
FILL IN THE BLANK
1. The maximum intensity of solar radiation available to the earth is called the ___________________
_______________________.
2. Gains and losses of heat for the planet can be described in terms of a __________
__________________.
3. Incoming solar radiation has relatively ________________ wavelengths, while re-radiated energy from the
earth’s surface is relatively _____________.
4. The zone of rapid change in density with depth is called the ______________________________.
5. Land and water respond differently to cycles of solar radiation because they have very different ___________
________________________.
6. Density of seawater is controlled primarily by changes in ______________________ and
___________________________.
7. A zone of rapid change in temperature in seawater is called the ____________________________.
8. If salinity is constant over depth, it is said to be ____________________________.
9. Circulation that is driven by the density differences caused by changes in temperature and salinity is called
_____________________________ circulation.
10. Density is usually converted to ____________________ values.
11. Areas in which water sinks are called _____________________ zones, while areas where water rises are called
__________________________ zones.
12. Surface ______________________________ means an area where waters are driven together.
13. ____________________ __________________________ are distinguished from one another by different
densities caused by temperature and salinity variations.
14. Water sampling bottles can be opened at specific depths by sending a
____________________________________ down a wire.
15. The process of obtaining a water sample at some depth is called a _________________________________.
16. An instrument that measures conductivity and temperature changes as it descends is a ________________.
17. _____________ ______________ _____________ ______________ depends on the difference in
temperature between surface water and water at 600–1000 m (2000–3300 ft) depth.
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18. When a water column is unstable and begins to mix, vertical _____________________ of the water takes place.
19. Where surface waters flow away from each other, a surface ______________________ occurs.
20. When there is a strong habitat relationship with organisms and water masses, these organisms are
_________________________ _______________________.
TRUE - FALSE
1. Sunlight reaching the earth’s surface never has an intensity equal to the solar constant.
2. The maximum intensity of solar radiation at the earth’s surface occurs in temperate latitudes.
3. The wavelength of re-radiated energy is longer than that of the incoming energy.
4. The layered water structure in the Pacific is the best studied.
5. There are no real seasons in the tropics.
6. Oceanographers typically measure density to five decimal places.
7. The angle at which the sun’s rays strike the earth changes dramatically from summer to winter at mid-latitudes.
8. The heat capacity of the land is lower than that of the water.
9. The salinity of mid-ocean waters is controlled primarily by large-scale precipitation/evaporation patterns.
10. Many combinations of salinity and temperature can produce the same density of water.
11. The mixed layer extends to a depth of about 500 m (1650 ft) in most areas of the world.
12. Increasing density with depth produces an unstable water column.
13. Areas where surface ocean winds or currents converge experience upwelling.
14. Upwelling and downwelling are very slow processes.
15. The densest water produced in the world’s oceans is North Atlantic Deep Water.
16. Water from the Mediterranean extends across the Atlantic at a depth of about 1000 m (3300 ft).
17. The water of the Indian Ocean is quite homogeneous.
18. Arrowworms always point north, or into the current.
19. Despite darkness, wind, waves, heat, or cold, data are taken, for there may not be a second chance on the
briny deep.
20. Antarctic Bottom Water is a water type.
MULTIPLE CHOICE
1. Heat that is absorbed at the sea surface is mixed downwards by
a. winds.
b. waves.
c. currents.
d. downwelling.
e. all of the above.
2. The layered structure of the oceans is a result of
a. the addition and loss of heat at the surface.
b. surface precipitation and evaporation patterns.
c. air movement driving surface water.
d. all of the above.
e. b and c above.
3. While the solar constant is about 2 cal/cm2/min, the highest average intensity of instantaneous solar radiation at
the earth’s surface is only about ________ cal/cm2/min because of atmospheric interference.
a. 0.5
b. 1.6
c. 1.2
d. 0.8
e. 1.9
4. What percent of incoming solar radiation is immediately reflected from the top of the atmosphere?
a. 31
b. 17
c. 24
d. 5
e. 8
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5. Osmotic pressure will
a. increases with increasing temperature.
b. drive salt water across a membrane toward fresh water.
c. drive fresh water across a membrane toward salt water.
d. a and b above.
e. none of the above.
6. Annual mid-ocean surface temperature changes in the tropics are about ________ °C.
a. 1–5
b. 0–2
c. 3–6
d. 2–4
e. 6–8
7. A zone with rapid changes in density with depth is called the
a. thermocline.
b. pycnocline.
c. densocline.
d. halocline.
e. isopycnal.
8. The densest water in the ocean basins
a. flows northward from Antarctica across the sea floor.
b. is created in the Weddell Sea.
c. moves as a result of thermohaline circulation.
d. a and c above.
e. all of the above.
9. In the open ocean
a. temperature is more important than salinity in determining density.
b. salinity is more important than temperature in determining density.
c. salinity is more important than pressure in determining density.
d. a and c above.
e. b and c above.
10. Sigma-t is a measure of
a. salinity.
b. density.
c. conductivity.
d. productivity.
e. will power.
11. Upwelling and downwelling water moves at rates of about
a. 0.5–1.0 m/day.
b. 0.3–2.5 m/s.
c. 0.1–1.5 m/day.
d. 1–4 m/s.
e. 2–6 m/day.
12. The thickness and horizontal extent of water layers in the oceans are related to
a. the latitude at which they form.
b. the rate at which they form at the surface.
c. the size of the surface region over which they form.
d. b and c above.
e. all of the above.
13. Sea surface temperatures in tropical latitudes in the summer are generally between _________ °C.
a. 25–30
b. 10–15
c. 5–20
d. 40–45
e. 50–60
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14. Water in the central North Atlantic at a depth of 1000 m (3300 ft) comes from
a. the Sargasso Sea.
b. the Red Sea.
c. the Gulf Stream.
d. the Mediterranean Sea.
e. the Black Sea.
15. A water mass with only one temperature and one salinity value over its entire extent is known as a
a. lens.
b. chaetognath.
c. water type.
d. water column.
e. water body.
16. Upwelling waters bring up ___________________ from deeper waters.
a. nutrients
b. decomposition products
c. manganese nodules
d. deep-water sediments
e. a and b above.
17. To maintain a constant thermal structure on earth, the planet must
a. gain heat from the sun.
b. lose heat to space.
c. create heat in its interior.
d. gain and lose approximately equal amounts of heat.
e. none of the above.
18. If we consider the heat budget of a small area of the ocean, among other things we must know is (are) the
a. total energy absorbed and heat re-radiated to space.
b. loss of energy due to evaporation.
c. transfer of heat into and out of the area.
d. warming and cooling of the atmosphere.
e. all of the above.
19. The thermocline extends from about
a. 500–2500 m.
b. 100–1000 m.
c. 300–1500 m.
d. 0–2000 m.
e. none of the above.
20. A CTD measures
a. conductivity.
b. depth.
c. temperature.
d. all of the above.
e. none of the above.
Visual Aids: Test Your Understanding of the Figures
1.
2.
3.
4.
Look carefully at the pattern of sea surface temperature in the Pacific Ocean illustrated in figure 6.4. Can you
explain why sea surface temperature at a given latitude tends to be higher on the western side of the ocean than
on the eastern side? Is this pattern repeated in the Atlantic and Indian Oceans?
Examine figure 6.8 carefully. In general, is density more dependent on temperature or salinity?
Look carefully at figure 6.14. What happens to Antarctic bottom water as it reaches the equator?
Examine figures 6.18c and 6.18d carefully. What is the approximate salinity and temperature of Antarctic
Bottom Water?
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Study Problem
1.
Deep horizontal movement due to thermohaline flow occurs at velocities of about 0.01 cm/sc. At this rate, how
long would it take North Atlantic Deep Water to travel from its point of origin near 60°N to roughly 40°S
(remember that the circumference of a very nearly spherical earth is 40,000 km)? Express your answer in years.
Answer Key For Key Terms and Test Your Recall
KEY TERMS
solar constant (I)
water type (IX,X)
downwelling (VII)
isopycnal (V)
water mass (IX,X)
chemical tracers (VIII)
FILL IN THE BLANK
1. solar constant
4. pycnocline
7. thermocline
10. sigma-t
13. water masses
16. CTD
19. divergence
upwelling (VII)
heat budget (I,II)
T-S curves (X)
sigma-t (VI)
CTD (XI)
2. heat budget
5. heat capacities
8. isohaline
11. downwelling, upwelling
14. messenger
17. ocean thermal energy conversion
20. biological indicators
divergence (VII)
thermocline (V)
hydrocast (XI)
convergence (VII)
tritium (VIII)
3. short, long
6. temperature, salinity
9. thermohaline
12. convergence
15. hydrocast
18. overturn
TRUE - FALSE
1.T 2.F 3.T 4.F 5.T 6.T 7.T 8.T 9.T 10.T 11.F 12.F 13.F 14.T 15.F 16.T 17.F 18.F 19.T 20.T
MULTIPLE CHOICE
1.e 2.d 3.b 4.a 5.c 6.b 7.b 8.e 9.d 10.b 11.c 12.d 13.a 14.d 15.c 16.e 17.d 18.e 19.b 20.d
STUDY PROBLEM
1. 3523 years
78