Music today: Billy Ocean, “Get Outta My Dreams and Into My Car” : 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 The Properties of Sea Water : The Properties of Sea Water What makes water so special?
Why is the ocean salty? Where’s the Water? : Where’s 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 Where did the water in the Oceans come from? : 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 The Water Molecule : The Water Molecule Water is a “Polar” Molecule : Water is a “Polar” Molecule Weak electrical attraction makes for “sticky” molecules
This explains its unique properties:heat capacitysurface tensiondissolving power Temperature vs Heat : 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) Sensible Heat vs Latent Heat : 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) Slide 9: Table 4.2 (6th edition) Slide 10: ice water vapor liquid water Exists in three states on the planet surface Slide 11: Changes of state Water co-exists on the Earth in 3 physical states: Slide 12: Changes of state always occur at constant temperature
The heat needed for a change of state is called latent heat Heat and the three Physical States of Water: : Heat and the three Physical States of Water: Slide 14: Evaporation from lakes, oceans, rivers, etc. occurs for temperatures lower than 100 oC But it requires more energy to do so Slide 15: Density of Pure Water Slide 16: Consequences… Slide 17: 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. Slide 18: 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 Slide 19: Energy removed from surface (evaporation) Energy liberated into the atmosphere (condensation) Major source of energy to power
the Earth’s weather systems Special Properties of Water : 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 Dissolving Power of Water : Dissolving Power of Water Why is the Ocean Salty? : 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 The Most Abundant Ions : 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 Ions in Sea Water : Ions in Sea Water Anions are negatively chargedCl-, SO4-
Cations are positively chargedNa+, K+, Ca++, Mg++ Measuring Salinity : 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 Where does Salinity come from? : Where does Salinity come from? Terrigenous input (rivers, dust, ash)
Dissolving old sediments (evaporites)
Steady State: Inputs equal Outputs Weathering of Rocks : Weathering of Rocks H2O + CO2 ---> 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 Residence Time : 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 Residence Time : 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? Slide 30: Adding salt lowers the freezing temperature: Seawater freezes at about -2 oC
Freezing removes fresh water, leaves salt The Hydrologic Cycle : The Hydrologic Cycle Evaporation - Precipitation : Evaporation - Precipitation Over the oceans, evaporation exceeds precipitation
The balance is restored by rain over the continents, returning water via rivers Desalination -- fresh water from the Oceans : Desalination -- fresh water from the Oceans Slide 34: Salt in the Ocean increases its density Slide 35: Ocean Surface salinities Evaporation vs Precipitation : Evaporation vs Precipitation Slide 37: Which processes change the
surface salinities ? saltier fresher evaporation precipitation sea ice formation sea ice melting freshwater runoff from land Slide 38: Which ocean is the saltiest? Which ocean is Saltiest? : 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 Slide 40: Surface salinities Evaporation, precipitation, and wind patterns
explain high/low salinity of Atlantic/Pacific. Summary: : 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