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Unformatted text preview: CHAPTER 5 CHAPTER 5 Water and Seawater Neutral atoms (or molecules): # electrons = # protons # Protons dictates element: H, He, Li, Be, B, C, N, O etc. Isotopes: same number of protons, different number of neutrons Carbon-12 (6 protons, 6 neutrons) Carbon-14 (6 protons, 8 neutrons…radioactive) Anions (negative charge): gain of one or more electrons Cations (positive charge): loss of one or more electrons H2O molecule One hydrogen H and two oxygen O atoms bonded by sharing electrons Both H atoms on same side of O atom Dipolar Hydrogen bonding Hydrogen bonding Polarity means small negative charge at O end Small positive charge at H end Attraction between + and – ends of water molecules to each other or other ions Fig. 5.3 Hydrogen bonding Hydrogen bonding Hydrogen bonds are weaker than covalent bonds but still strong enough to result in High surface tension High solubility of chemical compounds in water Solid, liquid, gas at Earth’s surface Unusual thermal properties Unusual density Water molecules in different states Water molecules in different states of matter (solid, liquid, gas). Fig. 5.5 Changes of state due to adding or Changes of state due to adding or subtracting heat Heat is energy (calories) Temperature is measurement of average vibrational and kinetic energy Unusual thermal properties of H2O Unusual thermal properties of H due to hydrogen bonding H2O has high boiling point (100oC) H O has high freezing point (0oC) 2 High latent (hidden) heats of Melting/freezing High latent (hidden) heats of Evaporation/condensation Water high heat capacity Calorie is amount of heat needed to raise the temperature of 1 gram of liquid water by 1o C temperature Water can take in/lose lots of heat without changing Unusual thermal properties of H2O Unusual thermal properties of H Rocks low heat capacity Rocks quickly change temperature as they gain/lose heat Global thermostatic effects Global thermostatic effects Moderate temperature on Earth’s surface Marine effect Equatorial oceans (hot) don’t boil Polar oceans (cold) don’t freeze solid Continental effect Oceans moderate temperature changes day/night; different seasons Ocean currents carry heat from tropics to poles Land areas have greater range of temperatures day/night and during different seasons Properties of Seawater: Salinity Properties of Seawater: Salinity Total amount of material dissolved in water Typical salinity is 3.5% (or 35o/oo parts per thousand) Six elements make up 99% of dissolved solids in seawater Fig. 5.12 o/oo = part per thousand = gram/kilogram ppm = part per million = mg/kg ppb = part per billion = microgram/kg Ionic bonds hold NaCl together. Water disrupts ionic bonds easily, and forms a hydration sphere around the charged ions. Na+ (positive) cation Cl- (negative) anion Dipolar water molecules are good at solvating (dissolving) many things. Measuring salinity Measuring salinity Evaporation Chemical analysis Principle of constant proportions Major dissolved constituents in same proportion regardless of total salinity (Na/Cl and salinity/Cl ratios are nearly constant) Measure amount of chlorine (chlorinity) Electrical conductivity Salinometer Salinity variations Salinity variations
Open ocean salinity almost constant: 33 to 38 o/oo Coastal areas salinity varies more widely Influx of freshwater lowers salinity or creates brackish conditions Greater rate of evaporation raises salinity or creates hypersaline conditions Salinity may vary with seasons (dry/rain) Processes that add/subtract water Processes that add/subtract water from oceans
Salinity decreases through: Salinity increases through: Precipitation (rain or snow) Runoff (river flow) Melting icebergs Melting sea ice Evaporation Formation of sea ice Processes that add/subtract water Processes that add/subtract water Hydrologic cycle describes Hydrologic cycle describes recycling of water near Earth’s surface Fig. 5.15 Processes that add/subtract Processes that add/subtract dissolved substances
Salinity increases through: Salinity decreases through: River flow Volcanic eruptions Atmosphere Biologic interactions Salt spray Chemical reactions at seawater seafloor interface Biologic interactions Evaporite formation Adsorption Surface ocean variation of salinity Surface ocean variation of salinity Polar regions: salinity lower, lots of rain/
snow and runoff Midlatitudes: salinity higher, high rate of evaporation Equator: salinity lower, lots of rain Thus, salinity at surface varies primarily with latitude Net evaporation from 20-45o Net precipitation from 45-65o 05_19 Surface ocean variation of salinity Surface ocean variation of salinity Fig. 5.20 Deep ocean variation of salinity Deep ocean variation of salinity
Surface ocean salinity is variable Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) Halocline, rapid change of salinity with depth ...
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- Fall '08