Music today: Billy Ocean,

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Music today Billy Ocean, Get Outta My Dreams
and Into My Car

• Available by Wednesday Find your Midterm Exam
  score at the class web site, under Lectures,
  April 26
• Scantrons and Short Answers will be returned at
  Labs next week

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The Properties of Sea Water

• What makes water so special?
• Why is the ocean salty?

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Wheres the Water?

• Reservoir Volume (106 km3) PercentOcean 1370
  97.3Ice (polar) 29 2.1Groundwater
  5 0.4Lakes 0.1
  0.01Atmosphere 0.01 0.001Rivers 0.001 0.
  0001

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Where did the water in the Oceans come from?

• Outgassing (H2O, CO2) of the Earth from
  volcanoes, early in its history
• Sedimentary rocks as old as 3.8 billion years!
• A much smaller amount from comets that pass by

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The Water Molecule
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Water is a Polar Molecule

• Weak electrical attraction makes for sticky
  molecules
• This explains its unique propertiesheat
  capacitysurface tensiondissolving power

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Temperature vs Heat

• Temperature is a measure of how fast the
  molecules in a substance are moving
• Heat is a measure of how much energy has to be
  put into (or gotten out of) a substance to change
  its temperature, or state (solid, liquid, gas)

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Sensible Heat vs Latent Heat

• Sensible heat is what we sense from different
  temperatures
• Latent heat is the energy needed to change state
  (ice to water, water to vapor)

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Table 4.2 (6th edition)
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Exists in three states on the planet surface
water vapor
ice
liquid water
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Changes of state
Water co-exists on the Earth in 3 physical states
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Changes of state always occur at constant
temperature The heat needed for a change of state
is called latent heat
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Heat and the three Physical States of Water
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Evaporation from lakes, oceans, rivers, etc.
occurs for temperatures lower than 100 oC
But it requires more energy to do so
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Density of Pure Water
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Consequences
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Consequences

• Bottom temperature of deep, cold lakes is always
  4 oC.
• Ice floats on the water surface, so fish survive.
• Pipes (or beer bottles) can freeze and burst.

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Surface tension - measure of how difficult it is
to stretch or break the surface of a liquid
Water has the highest surface tension of all
common liquids
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Major source of energy to power the Earths
weather systems
Energy liberated into the atmosphere
(condensation)
Energy removed from surface (evaporation)
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Special Properties of Water

• Density of solid is less than liquid
• Melting and boiling points are very high
• Highest heat capacity
• High heat of fusion and vaporization
• Tremendous dissolving power

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Dissolving Power of Water
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Why is the Ocean Salty?

• Total dissolved solids (called salinity)
• About 3.5 by weight (average seawater)
• Usually expressed as 35 0/00 (parts per thousand,
  ppt)
• Varies geographically according to Evaporation,
  Precipitation, and Rivers

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The Most Abundant Ions

• Chloride (Cl-) 19.0 g/kg
• Sodium (Na) 10.6
• Sulfate (SO42-) 2.6
• Magnesium (Mg2) 1.2
• Calcium (Ca2) 0.4
• Potassium (K) 0.4 35.2 g/kg

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Ions in Sea Water

• Anions are negatively chargedCl-, SO4-
• Cations are positively chargedNa, K, Ca, Mg

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Measuring Salinity

• Principle of Constant Proportionse.g., SO42-/Cl-
  is a constant, independent of salinity
• This means we need measure only one ion to get
  salinity i.e., Cl-
• Today salinity is measured quickly by electrical
  conductivity of sea water

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Where does Salinity come from?

• Terrigenous input (rivers, dust, ash)
• Hydrothermal vents
• Dissolving old sediments (evaporites)
• Steady State Inputs equal Outputs

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Weathering of Rocks

• H2O CO2 ---gt H2CO3 (carbonic acid)
• acid rain, pH 4-5 environmental concerns
  (HCl, HF, H2SO4)
• Dissolves rock minerals into ions, which travel
  down rivers to the ocean

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Residence Time

• How long do the various dissolved ions stay in
  the ocean? Depends on how reactive.
• Residence Time The average time spent by a
  substance in the Ocean Amount in Sea
  Rate entering or exiting

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Residence Time

• For water entering through rivers, the residence
  time is about Volume 1370x106 km3 (oceans)
  Flux 0.037x106 km3/yr (rivers)
  35,000 years.For Cl-, the residence time is 100
  Ma!For Fe2, the residence time is 200 yrWhich
  is likely to obey Constant Proportions?

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Adding salt lowers the freezing temperature
Seawater freezes at about -2 oC Freezing removes
fresh water, leaves salt
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The Hydrologic Cycle
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Evaporation - Precipitation

• Over the oceans, evaporation exceeds
  precipitation
• The balance is restored by rain over the
  continents, returning water via rivers

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Desalination -- fresh water from the Oceans
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Salt in the Ocean increases its density
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Ocean Surface salinities
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Evaporation vs Precipitation
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Which processes change the surface salinities ?
saltier
fresher
? evaporation
? precipitation
? sea ice formation
? sea ice melting
? freshwater runoff from land
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Which ocean is the saltiest?
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Which ocean is Saltiest?

• In spite of the fact that many more big rivers
  empty into the Atlantic than the Pacific, the
  Atlantic is actually significantly saltier
  because of the evaporation-precipitation cycle
  and the Isthmus of Panama the Indian is
  intermediate

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Surface salinities
Evaporation, precipitation, and wind
patterns explain high/low salinity of
Atlantic/Pacific.
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Summary

• Water is a polar molecule -- unique properties
  (melting pt, heat capacity, dissolving power,
  water denser than ice)
• Salinity is the total dissolved solids
• Salinity in the surface ocean varies by
  Evaporation - Precipitation
• Principle of Constant Proportions
• Residence Time in the Oceans