1. Ocean Water
Salts and Gases

2. The Dissolving Power of Water
Dissolving power results from polar nature of H2O molecule
Na+ and Cl- are held together by ionic bonds (attraction of opposite charges)
H2O reduces the ionic bonding and pulls Na+ and Cl- apart

3. Salinity in Oceans Salinity Average salinity in oceans = 35 ‰
Total amount of dissolved solids expressed in grams in 1 kg of water
Average salinity in oceans = 35 ‰
35 parts per thousand (ppt)
35 g/kg
Salinity variations
Due to differences in local rates of evaporation and precipitation (water budget)

4. Constituents of Sea Water
Most abundant seawater elements are sodium (Na+) + chloride (Cl-)
Major constituents: SO42-, Mg2+, Ca2+, K+, and HCO3-
Minor and trace elements also present

5. Seawater versus River Water
Chemical Constituent
Percent of total salt content
Ocean
River
Silica (SiO2)
Iron (Fe)
Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Bicarbonate (HCO3)
Sulfate (SO42-)
Chloride (Cl)
Nitrate (NO3)
Bromide (Br)
TOTAL -
1.19
3.72
30.53
1.11
0.42
7.67
55.16
.02
100.00
14.51
0.74
16.62
4.54
6.98
2.55
31.90
12.41
8.64

6. Salts in the Ocean Why is the ocean salty? Salts come from:
Rocks = cations
Gases from mantle
Why is the ocean not getting saltier?
Salts going in = salts going out

7. Salts Going Out Sea Sra Sea Spray Evaporites Biological Adsorption
Fecal pellets
Shell formation
Adsorption
Mid-ocean ridge magma

8. Principle of Constant Proportions
The amount of salt varies, but the relative proportions of ions are constant
Because of this principle, it is necessary to test for 1 salt ion (usually Cl) to determine total amount of salt present

9. Determining Salinity 1. Calculating Salinity
Salinity= x chlorinity (‰)
Cl-
2. Salinometers
Na+
Salinity determined by the electrical conductivity produced by dissolved salts
Deionized water
with salt

10. Factors Affecting Salinity
Precipitation
Evaporation
Run off
Freezing

11. Residence Times Ion Time in years
Average length in time that a substance remains in solution in seawater
Ion
Time in years
Chloride (Cl-)
Sodium (Na+)
Magnesium (Mg2+)
Sulfate (SO42-)
Potassium (K+)
Calcium (Ca+)
Manganese (Mn)
Aluminum (Al)
Iron (Fe)
80 million
60 million
10 million
9 million
6 million
1 million
7 thousand
1 hundred
Ions with longer residence times are most abundant in ocean

12. Effects of Salinity Freezing point depression; boiling point elevation
Disrupts Hydrogen bonding
(freezing point of seawater =-2°C)
2. Changes density
Pure water density = 1 kg/l
Seawater density = kg/l
3. Changes vapor pressure
↑ ‰, ↑ P

13. Desalination Fresh H20 from Salt H20 Methods Distillation
Electrodialysis
Reverse Osmosis

14. Gases in Seawater Major Gases: N2, O2 and CO2
O2 and CO2 important for life processes

15. CO2 and O2 with depth Surface (0m) ~ 200m - ~1,000m 1,000m – 4,000m
Oxygen (O2) abundant gas
Photosynthesis dominant
~ 200m - ~1,000m
Oxygen (O2) ↓
Carbon Dioxide (CO2) ↑
Respiration dominant
Organic matter decay
1,000m – 4,000m
O2 ↑ slightly
Oxygenated bottom waters
Cold salty oxygenated H2O sinks in polar region transported to depth
CO2 continues to ↑
Organic matter decay

16. Gases Summary Photosynthesis Respiration Organic matter (OM) decay
CO2 consumed; O2 produced
Therefore, O2 more abundant than CO2 in photic zone
Respiration
O2 consumed; CO2 produced
Organic matter (OM) decay
O2 consumed; CO2 produced
Respiration and OM decay
= ↑ CO2 below photic zone

17. The pH Scale An acid has excess [H+] (Hydrogen ions)
A base has excess [OH-] (Hydroxyl ions)
CO2 controls acidity
↑ CO2 = ↑ acidity
↓ CO2 = ↓ acidity
pH of seawater = ; Average = 7.8

18. Gases in Seawater Carbonate Buffering System
Dissolved CO2 in water acts as a buffer
Prevents large shifts in pH
Seawater too basic:
H2CO3  HCO3- + H+ (pH drops)
Seawater too acidic:
HCO3- + H+  H2CO3 (pH rises)

19. Gas Cycling O2 Cycling CO2 Cycling Photosynthesis produce O2
Respiration & decomposition of O.M. use O2
O.M. buried doesn’t consume all O2
Rocks consume O2
CO2 Cycling
Organisms use CO2 for tissue
Decay of organic matter releases CO2 back to ocean

20. Nutrients and Organics
Required for plant growth
Cycled by plant growth and decay
Organics used by organism or buried