1. Physical and Chemical Oceanography
Section 7 Part I: CHEMICAL COMPOSITION
Excellent Site for Review!

2. Salinity salt concentration in parts per thousand (ppt) Variance:
ocean average: 35 ppt (35%)
Variance:
Sea diluted with freshwater by:
River
Melting glaciers

3. From Section 4 Nutrient Cycles
Chemical Composition
fairly constant for millions of years
Salinity
Mainly: sodium, chloride ions
Smaller: sulphate, magnesium, hydrogencarbonate, potassium
From Section 4 Nutrient Cycles

4. Chemical Composition local changes can occur Volcanic activity Runoff
Atmospheric dissolution

5. 1. Volcanic Activity
Gases: CO2, Sulphur dioxide, hydrogen sulphide, hydrogen chloride
dissolve in atmospheric H2O
enter sea by precipitation
Submerged volcanoes at plate boundaries emit gases (chlorine)
Major source of chloride ions in sea

6. 2. Runoff Flow of water from land Rain, melted snow & ice
Drains to oceans directly
or from rivers
Passes through soil
Urban runoff into drains

7. 2. Runoff
Picks up pollutants – pesticides, fertilizers and oil-derived substances
food chains and webs increasing concentration at each trophic level
Example: industrial wastewater with mercury
Minamata Bay
Shellfish & organisms
Human consumption – neurological disorders, paralysis and death

9. 3. Atmospheric Dissolution
Dissolved gases:
Nitrogen (N)
nitrogen-fixing microorganisms make products for other organisms
Carbon Dioxide (CO2)
Photosynthesis
Oxygen (O)
Respiration
Gases dissolved are at equilibrium with atmosphere
Concentration of it depends on relative solubility, temperature and salinity of sea

10. Salinity Evaporation – salt stays behind hydrometer
Hypersaline (increased amount of salt)
Ex: lagoon – high temp. Evaporation
Ex: Dead Sea – extreme
Accumulation of solutes
10x saltier than ocean

11. Precipitation rain, snow Dilutes sea water, decreases salinity
Estuaries
Melting glaciers

12. Density temperature salinity Warm on top of cold, dense water
Temperature gradient

13. Density If temp. abruptly as depth = thermocline Ocean surface 25 ⁰ C
Shallow layer of warm on deep layer of cold
Ocean surface
25 ⁰ C
2000 m deep
1⁰C
depth
temperature

14. Density salinity density
halocline – abrupt change in salinity as depth
Lower salinity (lower density) on top of higher salinity (higher density)
Mixing occurs by wind blowing at the surface down to ~200 m
Turbulence and currents
Temperature changes

16. Dissolved Oxygen (DO)
temperature
Oxygen solubility
General rule:

17. Dissolved Oxygen Temp of H2O
O2 slightly less soluble in salt than fresh
Temp of H2O
Dissolved Oxygen Concentration Freshwater
0⁰C
14.6 mg/dm3
5⁰C
12.8 mg/dm3
10⁰C
11.3 mg/dm3
15⁰C
10.2 mg/dm3
20⁰C
9.2 mg/dm3
25⁰C
8.4 mg/dm3
What is the pattern?

18. D.O. surface layer = high d.o. D.O. removed by respiration of marine
Can be supersaturated by 2 processes:
Turbulence & mixing by waves causing atmospheric O2 to dissolve
Photosynthesis by algae
O2 as byproduct
D.O. removed by
respiration of marine
organisms

20. D.O. decreases to minimum as depth increases
Increases again as depth increases
Oxygen minimum layer – depth that concentration of DO is lowest
Between 100m and 1000m