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Ocean Water

Ocean Water. Salts and Gases. The Dissolving Power of Water. Dissolving power results from polar nature of H 2 O molecule. Na + and Cl - are held together by ionic bonds (attraction of opposite charges). H 2 O reduces the ionic bonding and pulls Na + and Cl - apart.

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Ocean Water

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  1. Ocean Water Salts and Gases

  2. The Dissolving Power of Water • Dissolving power results from polar nature of H2O molecule • Na+ and Cl- are held together by ionic bonds (attraction of opposite charges) • H2O reduces the ionic bonding and pulls Na+ and Cl- apart

  3. Salinity in Oceans • Salinity • Total amount of dissolved solids expressed in grams in 1 kg of water • Average salinity in oceans = 35 ‰ • 35 parts per thousand (ppt) • 35 g/kg • Salinity variations • Due to differences in local rates of evaporation and precipitation (water budget)

  4. Constituents of Sea Water • Most abundant seawater elements are sodium (Na+) + chloride (Cl-) • Major constituents: SO42-,Mg2+, Ca2+, K+, and HCO3- • Minor and trace elements also present

  5. Seawater versus River Water

  6. Salts in the Ocean Why is the ocean salty? • Salts come from: • Rocks = cations • Gases from mantle = anions • Why is the ocean not getting saltier? • Salts going in = salts going out

  7. Salts Going Out • Sea Sra • Sea Spray • Evaporites • Biological • Fecal pellets • Shell formation • Adsorption • Mid-ocean ridge magma

  8. Principle of Constant Proportions • The amount of salt varies, but the relative proportions of ions are constant • Because of this principle, it is necessary to test for 1 salt ion (usually Cl) to determine total amount of salt present

  9. Determining Salinity 1. Calculating Salinity • Salinity=1.8065 x chlorinity (‰) 2. Salinometers • Salinity determined by the electrical conductivity produced by dissolved salts

  10. Factors Affecting Salinity • Precipitation • Evaporation • River runoff • Freezing

  11. Residence Times • Average length in time that a substance remains in solution in seawater • Ions with longer residence times are most abundant in ocean

  12. Effects of Salinity • Freezing point depression; boiling point elevation • Disrupts Hydrogen bonding (freezing point of seawater =-2°C) 2. Changes density • Pure water density = 1 kg/l • Seawater density = 1.024 kg/l 3. Changes vapor pressure • ↑ ‰, ↑ P

  13. Desalination • Fresh H20 from Salt H20 • Methods • Distillation • Electrodialysis • Reverse Osmosis

  14. Gases

  15. Gases in Seawater • Major Gases: N2, O2 and CO2 • O2 and CO2 important for life processes

  16. CO2 and O2 with depth • Surface (0m) • Oxygen (O2) abundant gas • Photosynthesis dominant • ~ 200m - ~1,000m • Oxygen (O2) ↓ • Carbon Dioxide (CO2) ↑ • Respiration dominant • Organic matter decay • 1,000m – 4,000m • O2↑ slightly • Oxygenated bottom waters • Cold salty oxygenated H2O sinks in polar region transported to depth • CO2continues to ↑ • Organic matter decay

  17. GasesSummary • Photosynthesis • CO2 consumed; O2 produced • Therefore, O2 more abundant than CO2 in photic zone • Respiration • O2 consumed; CO2 produced • Organic matter (OM) decay • O2 consumed; CO2 produced • Respiration and OM decay • = ↑ CO2 below photic zone

  18. The pH Scale • An acid has excess [H+] (Hydrogen ions) • A base has excess [OH-] (Hydroxyl ions) • CO2 controls acidity • ↑ CO2 = ↑ acidity • ↓ CO2 = ↓ acidity pH of seawater = 7.5-8.5; Average = 8.0

  19. Gases in SeawaterCarbonate Buffering System • Dissolved CO2 in water acts as a buffer • Prevents large shifts in pH • Seawater too basic: • H2CO3 HCO3- + H+ (pH drops) • Seawater too acidic: • HCO3- + H+ H2CO3 (pH rises)

  20. Gas Cycling • Photosynthesis produce O2 • Respiration & decomposition of O.M. use O2 • O.M. buried doesn’t consume all O2 • Rocks consume O2 • O2 Cycling • CO2 Cycling • Organisms use CO2 for tissue • Decay of O.M. releases CO2 back to ocean

  21. Nutrients and Organics • Required for plant growth • Cycled by plant growth and decay • Organics used by organism or buried

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