1. Physical and Chemical Oceanography
Part I: CHEMICAL COMPOSITION

2. Salinity salt concentration in parts per thousand (ppt) Variance:
ocean average: 35 ppt (350/00)
Variance:
Sea diluted with freshwater by:
River
Melting glaciers
Units=ppt

3. Chemical (salt) Composition
fairly constant for millions of years
Salinity
Mainly: sodium, chloride ions
Smaller: sulfate, magnesium, hydrogencarbonate, potassium
So what percent on average is pure water—96.5% ,and 3.5% is salts
Remember hydrogencarbonate=bicarbonate
Potassium-1%
CSSMCPB-acronym???
Rule of constant proportion=fixed proportion
From Section 4 Nutrient Cycles

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

5. 1. Volcanic Activity
Gases: CO2, Sulfur, hydrogen sulfide, 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
Salinity can change

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
Bringing freshwater which will change salinity but this is known as freshwater inflow/glacial/iceberg melting
Runoff is dealing with bringing pollutants from the land into the water

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
So in this case salinity is not changed

9. 3. Atmospheric Dissolution
Gases dissolved are at equilibrium with atmosphere
Concentration of it depends on relative solubility, temperature and salinity of sea
Dissolved gases:
Nitrogen (N)
nitrogen-fixing microorganisms make products for other organisms
Carbon Dioxide (CO2)
Photosynthesis
Oxygen (O)
Respiration
Adding other chemicals into the water. In this case salinity is not changed

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. Salinity is variable across the ocean
High salt concentrations are usually in the middle of the ocean basins away from the mouths of rivers, which input fresh water. High concentrations are also in sub-tropical regions because evaporation rates are high and in landlocked seas in arid (no rain) regions. At high latitudes, salinity is low because the melting of ice dilutes seawater. As a general rule, salinity is low where precipitation is greater than evaporation, mainly in coastal or equatorial regions.

13. A closer look Relatively LOW salinity Relatively HIGH salinity
Teacher’s Note: Low salinity areas are circled in blue, high salinity areas in black. Salinity will increase with distance from land

14. WHY IS SALINITY IMPORTANT?
SALINITY IS ONE FACTOR THAT CONTROLS THE DENSITY OF OCEAN WATER

15. Density temperature salinity Warm on top of cold, dense water
Temperature gradient
WHEN WATER AT DIFFERENT DEPTH HAVE DIFFERENT DENSITIES --LAYERS OF WATER WILL FORM=OCEAN CURRENTS

16. Density If temp. abruptly as depth = thermocline
Shallow layer of warm on deep layer of cold
depth
temperature

17. 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

18. Pycnocline- rapid change in density with depth
Pycnocline- rapid change in density with depth. Is a function of the thermocline and halocline. B/c density is a function of temp and salinity. Temp. is the dominant factor influencing density
Show video—12 minutes

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

20. 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
Show overhead table comparing salt and freshwater
What is the pattern?

21. 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

23. 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