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Physical and Chemical Oceanography
SECTION 7 PART I: CHEMICAL COMPOSITION
Excellent Site for Review!
Salinity• salt concentration in parts per thousand (ppt)•ocean average: 35 ppt (35%)
• Variance:•Sea diluted with freshwater by:•River•Melting glaciers
Chemical Composition• fairly constant for millions of years
• Salinity•Mainly: sodium, chloride ions•Smaller: sulphate, magnesium, hydrogencarbonate, potassium
From Section 4 Nutrient Cycles
Chemical Composition• local changes can occur
1. Volcanic activity2. Runoff3. Atmospheric dissolution
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
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
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
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
Salinity• 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
hydrometer
Precipitation• rain, snow
•Dilutes sea water, decreases salinity• Estuaries•Melting glaciers
Density• temperature
• salinity
•Warm on top of cold, dense water•Temperature gradient
temperature
density
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
depth
temperature
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
salinity
density
Dissolved Oxygen (DO)• General rule: temperature
Oxygen solubility
Dissolved Oxygen• O2 slightly less soluble in salt than fresh
Temp of H2ODissolved 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 th
e pattern?
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
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