physics of seawater. water is … a chemical compound (h 2 o) made up of two atoms of hydrogen and...
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Physics of Physics of SeawaterSeawater
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Water is …Water is … a chemical compound (H2O) made
up of two atoms of hydrogen and one atom of oxygen;
in liquid state between the tempe-ratures of 0º C and 100º C;
perhaps the only substance that is present in vast quantities in solid, liquid and gaseous states.
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The water moleculeThe water molecule is lightis light is stable as liquid over a wide is stable as liquid over a wide
temperature-rangetemperature-range has high heat capacity and latent has high heat capacity and latent
heatheat freezes over, not under, andfreezes over, not under, and is an excellent solventis an excellent solvent
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Water stays liquid over a wide range of temperatures
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+ -
+ + + -
- -
- -
-
-
+ -
+ -
105°
+ -
+ + + -
- -
- -
-
-
+ -
+ -
109°
When water freezes When water freezes to ice, the angle of to ice, the angle of hydrogen bonding hydrogen bonding
expands from 105° to expands from 105° to 109°. 109°.
As the space taken by As the space taken by 27 water molecules is 27 water molecules is now used by 24 now used by 24 molecules, the density molecules, the density of ice is less than the of ice is less than the density of water, i.e., density of water, i.e.,
water freezes overwater freezes over..
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Temperature (°C)
Den
sity
(g
/cm
3 )
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1.03
1.02
1.01
1.00
0.99
Den
sity
(g
/cm
3)
Temperature (°C)
Salinity lowers water’sSalinity lowers water’s freezing pointfreezing point
andand
point of point of maximum maximum densitydensity
and raisesand raisesthe boilingthe boilingpoint.point.
Seawater Seawater therefore therefore freezes at freezes at ––2°C2°C and boils and boils at 103at 103°C.°C.
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Electromagnetic Spectrum of Sunlight
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22
24
23
25
26
27 28 29
37‰33‰31‰0°
20°
10°
Tem
per
atu
re (
°C)
35‰
Salinity
X
Y
The numbers for the density isoclinals here are the density factor [(= 1000 x (density – 1)] values, with density measured in gm/cm3.
Suppose we mix two water samples, X and Y, having different temperatures and salinities but the same density. What will be the temperature, salinity and density
of the resulting mixture? Where do we encounter such situations?
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SOFAR (Sound Fixing And Ranging) channel
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Heat (calories)0 200 400 600 800
This is the temperature
range for liquid water
0
150
50
100
-50
Heat is the energy needed to change the temperature of a body or material (e.g., 1 calorie is the heat needed to change the temperature of 1 gram of water by 1°C)
Tem
per
atu
re (
°C)
Tem
pera
ture
mea
sure
s th
e th
erm
al
stat
e of
mat
ter
Heat versus Temperature• Heat, the energy needed to change the temperature of a body, can be specific (i.e.,
temperature change at constant phase or state) or latent (i.e., state or phase change at constant temperature).
A
1. Start with 1 g of ice at -50°C
B
2. 25 cal of heat will change it to 1 g of ice at 0°C = ½ 50°C1g (Specific Heat)
calg°C
C
3. 80 cal of heat will change it from 1 g ice at 0°C to 1 g water at 0°C, i.e., 80 1g (Latent Heat)cal
g
D
4. 100 cal of heat will change 1 g water at 0°C to 1 g water at 100°C
= 1 100°C1g (Specific Heat)
calg°C
E
5. 540 cal of heat will change 1 g water at 100°C to 1 g water vapor at 100°C = 540 1g (Latent Heat)cal
g
F
6. 25 cal of heat will change 1 g water vapor at 100°C to 1 g water vapor at 150°C
= ½ 50°C1g (Specific Heat)calg°C
• This example shows how much heat is needed to change the temperature of 1 g ice at -50°C to 1 gWater vapor at 150°C.
• The following changes occur in this process− ice from -50°C to 0°C (this
involves specific heat)− ice to water at 0°C (this involves
latent heat)− water from 0°C to 100°C (this
involves specific heat)− water to water vapor at 100°C (this
involves latent heat)− water vapor from 100°C to 150°C
(this involves specific heat)
Let us use the following constants:Specific Heat = 1 for water and
½ for ice/vaporLatent Heat = 80 cal/g to melt ice
540 cal/g to boil water
calg°C
calg°C
Therefore,Total heat needed = (25+80+100+540+25) or 770 calories
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The 23½° tilt of Earth’s spin axis means that the two poles do not get the same amount of solar heat at the same time.
North pole is tilted toward the sun from about March 22 to about Sept 22, when south pole tilts away from the Sun.
Northern hemisphere thus has its longest day (or summer solistice) around June 22, and the shortest day (or winter solistice) around Dec 22, whereas the opposite occurs in the southern hemisphere.
Seasons typically characterize the temperate latitudes (23½°– 66½° N and S), therefore, whereas tropics receive Sunlight all year round. Source:
http://vortex.plymouth.edu/sun/sun3d.html
Do tropics have seasons?
Would seasons exist if the Earth’s spin axis was not inclined at all?
Northern hemi-
sphereMarch 21
June 22Sept 22Dec 22
Vernal equinoxSummer solistice
Autumnal equinoxWinter solistice
Southern hemi-
sphere
March 21Dec 22
Sept 22June 22
•NASA’s Earth Seasons
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http://geography.uoregon.edu/envchange/clim_animations/gifs/tmp2m_web.gif
Seasonal temperature variations can be explained in terms of the latitudinal and seasonal variations in the surface energy balance.
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Depth:0 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:0.05 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:0.1 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:0.2 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:0.5 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:1 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:2 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:3 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:4 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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Depth:5 Km
http://ingrid.ldgo.columbia.edu/SOURCES/.LEVITUS94/.ANNUAL/html+viewer?plotcoast=draw+land
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permanent in the tropics;
seasonal at temperate latitudes, i.e., present in summer, missing in winter; and
absent in the polar waters.
Therefore, thermocline (i.e., the inflection point
in temperature-depth graph) is ...
Dep
thTemperature
Tropical all year round, in summer at temperate latitudes.
Polar latitudes all year round, in winter at temperate latitudes
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32.5
33.0
30.0
24.0
18.0
33.5
34.0
34.5
35.0
35.5
36.0
36.5
37.0
37.5
38.0
42.0
Global variations in sea surface salinity
‰
:// . . / 39 2/ .http oceanusmag whoi edu v n schmitt html
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Precipitation-Evaporation (P-E) represents the difference between precipitation and evaporation.
Data: NCEP/NCAR Reanalysis Project. 1959-97 Climatologies Animation: Department of Geography, University of Oregon, March 2000 (http://geography.uoregon.edu/envchange/clim_animations/gifs/pminuse_web.gif)
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0° 20°S 40°S20°N40°N
- 50
50
0
Eva
po
rati
on
- P
reci
pit
atio
n (
cm)
Dry
Wet E - P
Salinity
Surface salinity of the world ocean is high where evaporation exceeds precipitation,
and low where the opposite holds.
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Salinity (‰)
Dep
th
Eq
uat
or 30°N
/S
Halo-cline
Well defined and permanent haloclines therefore exist at the equator and at the 30°N and 30°S latitudes:
• At the equator because high preci-pitation there makes the surface waters fresh/less salty.
• At the 30°N and 30°S latitudes because excess evaporation there makes the surface waters very salty.
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January 1986 sea surface (0-50 m)
salinity (‰)
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http://www.scivis.nps.navy.mil/~braccio/images/T_big.gif
Sea Surface Temperatures
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http://www.scivis.nps.navy.mil/~braccio/images/S_big.gif
Sea Surface Salinity
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http://www.scivis.nps.navy.mil/~braccio/images/E_big.gif
Ocean Temperatures at 160m Depth
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http://www.scivis.nps.navy.mil/~braccio/images/A_big.gif
Ocean Salinity at 160m Depth
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1.027
g/cm3
1.028 g/cm3
1.029
g/cm3
1.025
g/cm3
1.026
g/cm3
36 383432
Salinity (‰)
0
20
10
Tem
per
atu
re (
°C)
14001500
100200
300400
500
600
700
800
1000900
1100 12001300
Depth(m)
100200300400500600700800900
100011001200130014001500
Temp(°C)
15.014.212.110.09.08.0
13.212.76.44.94.03.53.02.61.5
Salinity(‰)
37.336.035.335.033.533.037.036.735.234.834.534.534.434.334.1
T-S plot for mapping the pycnolineTabulated below are the temperature and salinity data obtained at different depths at about 10°N in the central Atlantic. Note how the data clearly show the presence of very salty and warmer waters at 700-800 m depths. Pycnocline is clearly present here (due to the influx of the Mediterranean waters). Indeed, there was no need to plot the tem-perature, salinity and density depth-profiles separately to map this. Notice how easily
this insight could be drawn from the T-S plot itself!