Physical and Chemical Oceanography

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

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

3. 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 1932-1968 • 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 hydrometer • Evaporation – salt stays behind • 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 • Shallow layer of warm on deep layer of cold • Ocean surface 25 ⁰ C • 2000 m deep 1⁰C

14. 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) • General rule:

17. Dissolved Oxygen • O2slightly less soluble in salt than fresh What is the pattern?

18. D.O. • surface layer = high d.o. • 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