Thermocline is a
range of depths
1. TYPICAL TEMPERATURE PROFILES
(from Pinet, 1998)
thermistor
2. CTD – ConductivityTemperature-Depth Recorder
(from Pinet, 1998)
3.
Celsius Temperature = Thermodynamic Temperature – 273.15ºK
Measured with ITS90
T68 = 1.00024 T90
4
(NORTHERN HEMISPHERE)
(from Pinet, 1998)
4
(NORTHERN HEMISPHERE)
(from Pinet, 1998)
5. Seasonal variability of sea surface temperature throughout the ocean
PRESSURE
Pressure = Force / Area
Pressure = Mass * Gravity / Area
Mass = Density * Volume
Pressure = Density * Volume * Gravity / Area
Volume/ Area = Depth
Pressure = Density * Gravity * Depth
P    g  z

6. PRESSURE


Mixed
Layer
Pycnocline
z1
z2
z
z3
-z
Pz
DENSITY CONSTANT
Pz = -  g z
Pz
-z
DENSITY STRATIFIED
Pz = -Σ13  ng zn
-z
Pz
DENSITY VARIES CONINUOUSLY
WITH DEPTH
Units: N/m2 = Pa
1 m depth ~ 1 db ~ 104 Pa
z
Pz   0  z gdz
SALINITY
Old Definition: “The salinity of a sample of sea water represents the total mass of
solid material dissolved in a sample of sea water divided by the mass of the
sample, after all the carbonates have been converted into oxide, the bromine
and iodine replaced by chlorine, and all organic matter completely oxidized.”
Absolute Salinity: “ratio of the mass of dissolved material in sea water to the
mass of sea water.” ----- can not be measured in practice.
Practical Salinity: is defined in terms of the ratio
Electrical conductivity of a sea water sample at 15ºC and one standard atmosphere……. = K15
Conductivity of a KCl solution in which the mass fraction of KCl is 0.0324356 at same T and P
If K15 = 1, then the Practical Salinity is 35
S = a0 + a1 K15½ + a2 K15 + a3 K153/2 + a4 K152 + a5 K155/2
where:
a0 = 0.0080
a1 = -0.1692
a2 = 25.3851
a3 = 14.0941
a4 = -7.0261
a5 = 2.7080
Σai = 35.000
Good for 2 < S < 42
Major Constituents
The concentrations of these
major constituents are
conservative. They are
unaffected by most biological
and chemical processes.
This is related to the principle
of constant proportion
Cl- 18.98/34.4 = 55%
Na+ 10.556/34.4 = 31%
Residence Time = Concentration (mass/vol)/Rate of supply (mass/vol/time)
Where do the Salts come from?
high
temperate
subtropical
7.
(from Pinet, 1998)
8.
(from the Navy Coastal Ocean Model)
9. Latitudinal variations
in surface salinity
(Pinet, 1998)
High evaporation in subtropics (wind and heat) causes high
surface salinity
What would temperature look like?
37
Salinity
30
34
31
20
Temperature
10
TEMPERATURE
10. WATER DENSITY
density anomaly (kg/m3)
23
24
25
26
27
depth (m)
Equator
1000
2000
Density Profiles in
the Open Ocean
Tropics
High Latitude
3000
4000
Density Anomaly σt = Density - 1000
Specific Volume  = Inverse of Density
11.
(from Pinet, 1998)
Equation of State (EOS-80)
Determines water density from T, S, and P
 (S ,T , P )   (S ,T ,0)1  P / K (S ,T , P )  1/  (S ,T , P )
 (S ,T ,0)  1/  (S ,T ,0)  A  BS  CS 3 / 2  DS 2
K (S ,T , P )  E  FS  GS 3 / 2  (H  IS  JS 3 / 2 )P  (M  NS )P 2
A through N are polynomials
T is temperature in oC
S salinity
P pressure in bars
K is the secant bulk modulus (change in volume
as pressure is changed)
A
B
C
D
T0
999.842594
8.24493E-1
-5.72466E-3
4.8314E-4
T1
6.793952E-2
-4.0899E-3
1.0227E-4
T2
-9.095290E-3
7.6438E-5
-1.6546E-6
T3
1.001685E-4
-8.2467E-7
T4
-1.120083E-6
5.3875E-9
T5
6.536332E-9
Specific Volume Anomaly
E
F
G
T0
19652.21
54.6746
7.944E-2
T1
148.4206
-0.603459
1.6483E-2
T2
-2.327105
1.09987E-2
-5.3009E-4
T3
1.360477E-2
-6.1670E-5
T4
-5.155288E-5
H
I
J
T0
3.239908
2.2838E-3
1.91075E-4
T1
1.43713E-3
-1.0981E-5
T2
1.16092E-4
-1.6078E-6
T3
-5.77905E-7
M
N
T0
8.50935E-5
-9.9348E-7
T1
-6.12293E-6
2.0816E-8
T2
5.2787E-8
9.1697E-10
Check values:  (35 ,25 ,0)  1023 .343
 (S ,T , P )   (S ,T , P ) 
 (35,0, P )
 (35 ,5,1000 )  1069 .489
12. Effects of Salinity on the Properties of Seawater
Lowers freezing point
Lowers temperature
of maximum density
Lowers evaporation
rate
Seawater freezes
before reaching
max density
-1.33
A lake turns over as it
freezes
The ocean remains
stratified as it freezes
24.7
(from Pinet, 1998)
13.
90 % of Ocean Water
Mean T & S for
World Ocean
Greater influence of salinity on density
14. Effects of Temperature and Salinity on Density
x 10-4 oC-1
1 
    
  T 
Thermal Expansion
x 10-4 S-1

1   
 
  S 
Saline Contraction
Density changes by 0.2 kg/m3 for a T change of 1oC,
and by 0.8 kg/m3 for a S change of 1.
Potential Temperature
In situ and Potential Temperature in the Mindanao Trench (from Millero’s home page)
Depth
Salinity
In situ
Theta
Sigma -t
Sigma-Theta
1455
34.58
3.20oC
3.09
27.55
27.56
2470
34.64
1.82
1.65
27.72
27.73
3470
34.67
1.52
1.31
27.76
27.78
4450
34.67
1.65
1.25
27.76
27.78
6450
34.67
1.93
1.25
27.74
27.79
8450
34.69
2.23
1.22
27.72
27.79
10035
34.67
2.48
1.16
27.76
27.79
Temperature a water parcel would have if raised adiabatically to the surface
15. Example of in-situ and potential temperature
2
3
27.8
4
2000
σt
T
27.4
0
depth (m)
depth (m)
27.4
0
1
4000
1
2
3
27.8
4
2000
4000
6000
6000
T
σt
8000
8000
10000
10000
Θ
How do we convert to potential temperature?
σΘ
σΘ
Θ
Effect of pressure on density
  T   dp
o
C
T
g


 1  2  10 4
p Cp
db
Data off
Antarctica
Cp  4  10 4 J /(kg oC )
Γ is the
adiabatic
lapse rate
potential
in-situ
~0.1º change at 1000 m
~0.3º change at 3000 m
Γ can also be obtained from Unesco
Technical Papers in Marine Science # 44 by
Fofonoff and Millard, Unesco 1983
Density Ratio
T
R   P
S

P

Relative importance of thermal expansion and haline contraction.
Tells us whether temperature or salinity gradient is most important in stratification
Example in Easter Island
T
R   P
S

P

SOUND SPEED
Sound is a wave that travels efficiently in water at a speed given by this
Thermodynamic expression.
1   
 
2
C
 P 
Eta is the entropy (normalized energy of the system)
A simpler form of that equation is:
C = 1449 + 4.6 T – 0.055 T 2 + 1.4 (S – 35) + 0.017 D (m/s)
16. C = 1449 + 4.6 T – 0.055 T 2 + 1.4 (S – 35) + 0.017 D (m/s)
Cair = 330 m/s ~ 660 kn
Depth (m)
SOFAR Channel and Acoustic Shadow Zone
(SOund Fixing And Ranging )
(From Tomczak’s Web Site)
Light Penetration in Sea Water
turbid
coastal
water
k=2
clear ocean water
k = 0.2
Iz = Io e –k z
k = vertical attenuation coefficient (m-1)
k = 0.02
(fraction of that entering at the surface)