1. Chap 6 Water & Ocean Structure
Physical Oceanography
2. Water and Heat
Sun is exclusive
source of energy
driving ocean and
atmospheric currents.
The Sun radiates
throughout the
electromagnetic
spectrum, but principle
radiation is in visible
part of the spectrum.
Visible light is strongly
absorbed by seawater
3. Heat – energy produced by random
vibration of atoms or molecules.
Temperature – object’s response to
an input or removal of heat.
Specific heat – heat required to
raise the temperature of 1 g of
substance by 1 °C. (calories / g)
4. Infrared Energy
in clear water, only
10% reaches 25 m,
only 0.5% reaches
100 m, .0025%
reaches 200 m
essentially all
energy gain in the
oceans takes place
in upper 10 -100 m
of water
5. Concept of Steady State
Averaged over the globe and over
a year, the Earth loses as much
energy as it gains.
Green house effect may be
changing the steady state
6. There is a net gain of energy at low latitudes
and a net loss of energy at high latitudes.
This latitudinal difference is energy gain and
loss drives both ocean and atmospheric
circulation.
All energy exchange by the oceans occurs at
the surface
This exchange of energy controls the
temperature of ocean water masses
7. Density
Mass / volume (g / cm3)
Density depends on temperature and
salinity
Ocean density ranges from 1.02 to 1.03
g/cc.
Density differences, together with
winds, are the principal factors
determining ocean currents.
8. Freezing Water
Density curve (6.6) shows the
relationship between the temperature or
salinity of a substance and its density.
9.
10. Water density decreases as the water
freezes
Angle between water molecules expand
from 105 ° to 109 °
Forms a crystalline lattice – less dense,
hence ice float.
11. Sensible heat loss – detectable decrease in
heat, measured with a thermometer, before
ice freezes
Latent [hidden] heat of fusion – amount of
heat removed to form ice per g of water (80
calories)
This process of freezing and thawing
moderates global temperature swings. Why?
12. Review the Concepts
Heat is transmitted in the ocean in
which wave length?
Define density
The density of a parcel of seawater will
be affected by which factors
13. Evaporating Water
Latent
heat of evaporation – amount of
energy required to break hydrogen
bonds
585 cal / g at 20 °C
Why such a big difference between
latent heat of evaporation and the latent
heat of fusion?
14. Sea Water vs. Pure Water
Solids dissolved No solids, water
lowers specific heat requires 1 cal to
by 4% (heats faster) heat up vs. 0.96 cal
Ions also interfere sea water.
with the freezing No ions to interfere
point, the saltier the with the freezing
lower the freezing point
point
15.
16. Solar Energy Inputs
the sun 'makes a direct hit' at equator, while
the same sunlight is spread over a larger area
at the poles.
This is just another way of showing that the
equator is heated up more than the north or
south poles of the Earth.
This uneven heating of our round globe
causes the air at the equator to rise, cool, and
then wring out its moisture as rain.
17.
18. The equator, then, is a zone of low
pressure systems and lots of
rainfall.
This zone extends from roughly 5°N to
5°S of the equator.
The air doesn't keep rising forever.
It eventually reaches an altitude where
it is the same temperature (and density)
as the surrounding air.
19. Itthen spreads out laterally, both in a
north direction, and in a south direction.
As it moves poleward (either north or
south from the equator), the air
continues to cool, and finally, sinks.
Where it sinks, the pressure is high.
Heat budget is balance (p.163, f. 7.10)
20.
21. Density Structure of the Ocean
Winds are the primary driving force of the
surface circulation, which is also called wind-
driven circulation,
density differences drive the deep, or vertical,
circulation of the oceans.
The density of seawater is controlled by
temperature and salinity, so the deep
circulation is also called the thermohaline
circulation.
22. Review the Concepts
Contrastsea water and fresh water
What causes the seasonal changes?
Why the poles are cold?
23. Temperature differences as small as a few
hundredths of a degree and salinity
differences of a few parts
in a hundred thousand can be important.
Both temperature and salinity are
conservative properties of seawater, that is,
there are determined by processes occurring
at the surface.
24. Salinity
Salinity refers to the weight fraction of
dissolved solids in water.
Average salinity of seawater is about
35‰ (‰ and ppt mean “parts per
thousand).
Principal processes that change salinity
are:
1. dilution (by rainwater and river water)
25. 2. Evaporation freezing (& thawing)
of sea ice
Salinity changes occur only at the
surface of the ocean
26. Because temperature and salinity
change only at the surface density
changes occur only at surface
Water masses can be identified by their
temperature-salinity characteristics.
Density, together with winds, govern
ocean currents
27. Ocean Structure
Upper 100-500 m to have uniform
temperature and salinity because of
mixing by waves.(6.13)
Below this, to a depth of ~1000 m,
Temp., Salinity, and density change
( Thermocline, Halocline,
Pycnocline) (6.12)
28.
29. Indeep water, temperature, salinity and
density are relatively uniform
This structure varies latitudinally. At
mid-latitudes, it also varies seasonally:
upper mixed layer will deepen in
summer;
thermocline might largely disappear in
winter
30.
31. Sound
Is a form of energy transmitted by rapid
pressure changes in an elastic medium.
Intensity decreases as it travels through
seawater until eventually is absorbed
and converted into heat
Speed is 1,500 m / s, almost five time
the speed in air
32. Echolocation
Marine mammals use
sound rather than light
to “see” in the ocean
Echolocation –use of
reflected sound to
detect environmental
objects
MM use echolocation
to detect prey and
avoid obstacles
33. Speed of sound increases as temperature
and pressure increases (6.21)
Travels faster at the surface than in deeper,
cooler water.
Minimum speed at 600 – 1,200 m
Below this depth the pressure offsets the
temperature and speed increases again
34.
35. SOFAR Layer
Sound Fixing and Ranging
Transmission of sound in this minimum-
velocity layer is very efficient because
refraction tends to cause sound energy to
remain within the layer (6.20)
Loud sounds made at this depth can be
heard for thousands of kilometers
Sound generated in the India Ocean was
hear as far a way as the Oregon Coast (Box
6.1)
36.
37. SONAR
Sound Navigation and Ranging
Active SONAR – projection of short
pulses of high frequency sound to
search for objects in the ocean.
Operator can tell direction, size,
heading and even the composition by
analyzing the composition of the
returned ping
38.
39. Side-Scan Sonar – towed behind a
vessel (6.22)
Used for geological and archeological
studies, and the location of downed
ships and airplanes
40. Review the Concepts
What kind of temperature does most of the
world ocean has?
What is characteristic about the ocean's deep
sound channel (sofar layer) ?
What is called a zone in which the ocean's
salinity increases rapidly with increasing
depth?
Which zone does the most pronounced or
marked all year around thermoclines exist?