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

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

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

Chemical Composition local changes can occur Volcanic activity Runoff 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 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

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

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

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

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

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

Dissolved Oxygen (DO) temperature Oxygen solubility General rule:

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?

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

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