1. Physical Properties of Ocean Water
Lecture 3
Physical Properties of Ocean Water
- Salinity and Light -

2. Part 1 - What’s in seawater

3. Salinity Freshwater Seawater 101.07 kg/100 l 103.6 kg/100 l
How much salt is in seawater?
Freshwater
Seawater
kg/100 l
103.6 kg/100 l

4. Salt in the ocean - 5.5 x 109 tonnes
- cover the earth to a depth of 45 m

5. Component Ions in Seawater

7. Comparison of fresh and salt water

8. -measured in ppt (parts per thousand or ‰)
Ion Concentration
-measured in ppt (parts per thousand or ‰)
Average in seawater is about ‰
(freshwater is about 3.3 ‰)

10. Salinity – Red Sea
- evaporation
- isolation from open ocean
- little freshwater input
41‰
33‰

12. The effects of all these ions
Seawater freezes at a lower temperature
Fresh water
Salt water
Liquid
Ice

13. Part 2 – How do we measure salinity?

14. Forchhammer - Law of Constant Proportions
Ratio of ions  Na+ : Cl- : SO4-- : Mg++: K+ : Ca++ :CO3--
Constant - worldwide
Calculation of salinity from chlorinity
chlorinity - wt. of Cl-, Br-, I- ions
Salinity % = x chlorinity

15. Salinity and conductivity

16. Salinity and refraction

18. Refractometer

19. Part 3 – Where do all these ions come from?

20. Sources – provide elements to system
Sinks – remove elements from system

21. Sources of Inputs of Salts in Oceans
Rivers (largest transport of chemicals to ocean)
Rain + CO2  H2CO3
Si, Al, Na, K, Mg
Volcanoes
Cl, S, CO2
Dust / Rain
Fe, Si
Anthropogenic
CO2, P

22. Example 2 Geochemical Cycle

23. Cycling of Sea Salt Volcanic activity Sediments uplifted
H2S
Rainfall
Volcanic activity
Cl-
SO4-2
Sediments
uplifted
River discharge & runoff
Ca+2 K+
Mg+2
CO3-2
Ca+2
SO4-2
Mg+2 N+
Organisms die
adsorbed by clays
Leaching from rocks
precipitation
Bottom sediments

24. Hydrothermal Vents: A Source & SINK Minor source
Consume other elements
Lead, Sulfur, Copper, Iron, Cobalt, Gold
Mostly Gypsum & Zinc

25. Sinks Biological activity
Interaction with particulate matter: clays and organic matter absorb dissolved metals

26. Residence time
Residence time = AMOUNT OF ELEMENT IN OCEAN RATE OF ADDITION OR REMOVAL

27. Residence Time - Concentration
Element Res. Time (yrs)
Na 60 x 106
Cl 80 x 106
Mg 10 x 106
K 6 x 106
SO4 9 x 106
Ca 1 x 106
Mn 7 x 103
Fe x 103
Concentration
Crust (%) Ocean (mg/l)

28. Gases in Ocean Water

29. Gases in Atmosphere & Oceans
Percent Gas Phase by Volume
Gas
Atmosphere
Surface Ocean
Total Ocean N2
79%
48%
11% O2
21%
36% 6%
CO2
0.04%
15%
83%

31. Seawater pH Pure water pH = 7 Seawater pH = 7.5 – 8.1
Seawater is very well buffered!

32. The Carbonate System in Seawater
CO2 in seawater is controlled by:
1. Exchange with the atmosphere
2. Photosynthesis/Respiration:
6CO2 + 6H2 O  C6 H12 O6 + 6O2

34. Importance of CO3--
CO3--

35. Normal pH range of seawater
100%
50% 0%
HCO3-
(bicarbonate
ion)
H2CO3
(carbonic acid)
CO3--
(carbonate ion)
Relative abundance of carbonic acid, bicarbonalte ion and carbonate ion in seawater
Average pH of seawater
Normal pH range of seawater pH

37. Light Transmission transparent in visible part of spectrum
Absorbed as is goes deeper in the water column
strongly absorbs infrared (heat) and ultraviolet (prevents damage to DNA)

38. Light penetration

39. Absorption of frequencies of light

42. Light penetration and location

43. Photosynthesis and Light
Photosynthetic Rate (%O2/mim)
Irradiance (mE/m2/s

44. Light Depth Percent surface light Turbid coastal water5 10 15 20 25 30 35 40 45 50
Depth
Clear open ocean water
Limit for foliose algae
Limit for Laminaria (kelp)
Percent surface light

45. Next time
Tides