“If everything seems tobe going well,

Obviously you’veoverlooked something!”

“If Barbie is so popular,why do you have to buy

her friends!

OceanographyOceanographyLecture 10Lecture 10

a.a. Density of SeawaterDensity of Seawaterb.b. TS DiagramsTS Diagramsc.c. Density structure of the oceanDensity structure of the ocean

Density:Density:Temperature, Salinity, and PressureTemperature, Salinity, and Pressure

DensityDensity: : !! S,T,PS,T,P = 1.02594 g/cm = 1.02594 g/cm33 must be known to the 5 must be known to the 5thth

decimaldecimal

The symbol used to express density is The symbol used to express density is "" ( (sigmasigma).).

""TT (or (or ""##)) = (specific gravity = (specific gravity –– 1) x 1000 1) x 1000

Specific gravitySpecific gravity = density of a substance/density of water = density of a substance/density of water

It is the density of a parcel of water of specific T and SIt is the density of a parcel of water of specific T and Sthat is brought up to the surface (no pressure effect!)that is brought up to the surface (no pressure effect!)

""TT = ((1.02594/1.0000) = ((1.02594/1.0000) –– 1) x 1000 = 25.94 1) x 1000 = 25.94No units!No units!

T-S Diagram

0

5

10

15

20

25

29 31 33 35 37

Salinity (‰)

Te

mp

era

ture

(°C

)

!t 23.0

!t 28.0

!t 24.0 !

t 25.0 !t 26.0

!t 27.0

Increasing density

Density:Density:Point D is denser than point B

5°C Warming leads tohigher change in densityat high T vs. low T

Density Structure of the Oceans: Depth

The boundary zone between the surface-water and deep-water layers isthe pycnocline layer (density gradient): Transition zone where “light”surface water grades into “denser” deep-water layers.

Density Structure of the Oceans: Depth

The Ocean can be divided into three structures:Surface layer; Pycnocline; Deep-layer.

Pycnocline: Amounts to ~18% of the Oceans volume)

Uniformity of Ocean Water?

75% of the total Ocean volumehave a! Temperature: 0-5°C! Salinity: 34-35‰

Oceans’ depths are filled withcold water (colder than the~17.5°C average T of theOceans’ surface waters). Most of this water must haveoriginated in polar latitudes,where it was chilled by losingheat to the frigid air. Uniformity of T and salinityof subsurface seawater fromOcean to Ocean suggests thatOcean basins are open systems!

Temperature vs Depth

0

1000

2000

3000

4000

5000

-0.5 4.5 9.5 14.5 19.5

Temperature (°C)

De

pth

(m

)

In situ T

Potent. T

Salinity vs Depth

0

1000

2000

3000

4000

5000

34 34.5 35 35.5 36

Salinity (‰)

Dep

th (

m)

Vertical Temperature & SalinityT-S Diagram

-1

4

9

14

19

24

34 34.5 35 35.5 36 36.5 37

Salinity (‰)

Te

mp

era

ture

(°C

)

!t 23.0

!t 28.0

!t 24.0

!t 25.0

!t 26.0

!t 27.0Water is lighter at surface

Every “bend” represents anew water mass

Deep water circulation: A model

CaballingCaballing::When two water massesWhen two water massesmerge, the combination ofmerge, the combination oftheir temperatures andtheir temperatures andsalinities results insalinities results indensification densification vertical verticaladvectionadvection of water of water

Latitudinal Difference in Density

T has a much greaterimpact than S onDensity!

Light

Heavy

High latitudes (>60ºN and S) Deep water circulation: A model

Density Structure of the Atlantic Ocean: A model

Density Structure of the Pacific Ocean

Density Structure of the Indian Ocean