Water Unit Introduction

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Water Unit Introduction

• Outline
• Unique chemistry
• Distribution on planet - changes with time
• Hydrologic cycle - redistribution, climate
  effects
• Ocean circulation - basic wind thermohaline

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• Chemically unique because it
• exists in all three phases at atmospheric temp
  pressure (high melting and boiling points for
  size bond type- ammonia-NH3-mass 17, MP -78, BP
  33) and is the only substance that does this!
• has covalent bonds for molecule, hydrogen bonds
  for liquid/solid phase (10x stronger than usual
  inter-molecular bonds, but weaker than metal or
  ionic bond)

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• Chemically and physically unique because it has
• high heat capacity - 4.2 J/g/K- i.e., takes more
  energy to raise temp, therefore stores more,
  important for spreading planets heat
• high heat of fusion (solid ltgt liquid 335
  J/g/ºK) and vaporization (liquid ltgtgas 2400
  J/g/ºK) so more effectively transfers heat when
  changing phase in atmosphere/ocean
• conducts heat more readily as a liquid

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• Water is chemically and biologically unique
  because it
• has high surface tension so forms drops helps
  make good cell membranes
• can dissolve other compounds very easily (most
  common solute), so can transport many things,
  e.g. NaCl, nutrients
• mediates or facilitates most chemical reactions
  in living systems (e.g., takes water to
  photosynthesize) - neutral pH

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Water is physically unique because it is less
dense as a solid (ice) than as a liquid.
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Distribution on Earth Water, water everywhere,
nor any drop to drink. Coleridge, Rime of the
Ancient Mariner
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Hydrologic Cycle (in 103 km3)
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Effects of global warming on water cycle
Global warming (temperature increase)
Speeds up global water cycle

• More extreme weather events
• Droughts
• Storms
• Floods

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Projected Changes in Annual Precipitation for the
2050s
The projected change is compared to the present
day with a 1 increase per year in equivalent CO2
Source The Met Office. Hadley Center for Climate
Prediction and Research
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Global Precipitation Trends ( per decade) 1900
- 1994
Green increasing, Brown decreasing
Source Watson 2001
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U.S. Precipitation Trends 1901 to 1998
Green increasing, Brown decreasing All
stations/trends displayed regardless of
statistical significance
Source National Climatic Data Center/NESDIS/NOAA
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Extreme Precipitation Events in the U.S.
Source Karl, et.al. 1996.
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