Chemical and Physical Features of Seawater and the World Ocean

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Chemical and Physical Features of Seawater and
the World Ocean

• Ch. 3

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Objectives

1. Understand the basic chemical and physical
   properties of water seawater.
2. The origin of the seas

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Global Water Distribution Estimate (Scroll down
to global water distribution table)
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What percentage of the human body consists of
water?

• Babies 78
• One Year old 65
• Adult men 60
• Women 55
• Why do women have less water?
• They have a higher percentage of fat --gt hold
  less water

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What about marine organisms?

• Most consist of about 80 of water
• Jellyfish?
• Over 95!!

Recently discovered species of sea anemone,
Aleutian Islands
Nomura Jellyfish, Japan
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Water is unique. Why?

• Naturally occurs in all three states
• Solid, liquid, and gas
• No other substance on earth does this

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Element vs. Molecule

• Whats the difference?
• Element
• Composed of a single type of atom (only about 118
  of these in the world)
• Molecule
• Combination of two or more atoms
• What does water consist of?

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Molecular Makeup H2O

• Opposite charges
• Oxygen is (-)
• Hydrogen is ()
• Draw a water molecule
• Forms weak hydrogen bonds
• Why is it important that water has weak bonds??

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Hydrogen bonds

• This is what allows water to go from state to
  state
• Molecules in constant motion
• What happens when they speed up?
• They get warmer and then . . . ?

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Fast and Slow molecules

• The bonds break and water enters the vapor state
• What about when it cools?
• Movement slows down, becomes dense until is slows
  down so much that. . .

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It freezes!

• What temperature is water at its most dense
  form?
• 4º C. Is it frozen at this temperature?
• Why is this important?
• What if ice were waters densest state?

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The Changing Molecular Structure of H2O
What do you notice about the structure of each
state?
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Bottom line

• Seawater becomes denser as it cools, until it
  freezes.
• Ice is less dense than liquid water

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Heat and Water

• Water has the highest latent heats of melting and
  evaporation
• How does ice keep our drinks cold?
• It takes a lot of heat to melt ice
• Heat breaks hydrogen bonds in ice instead of
  heating up your drink --gt drink stays cold
• Why do we sweat?
• H2O has high heat capacity
• Absorbs a lot of heat w/ a relatively small
  increase in temp
• Why is this important for marine organisms?
• Not subject to drastic temp change

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The Universal Solvent

• Why can water dissolve more things than any other
  substance?
• Its both (-) and () charged!
• Pulls apart salt
• Sodium (Na) Chloride (Cl-)

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What Makes up Seawater?
Ions (charged particles) enter the sea from
different places
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Composition of Seawater

• Theres a little bit of everything
• 6 ions compose over 99 of dissolved solids in
  seawater
• NaCl make up over 85
• This composition stays relatively the same
• Rule of constant proportions
• Why is this important?
• Sea organisms rarely have to deal with changes in
  the ratios of various ions --gt easier to control
  their internal water/salt balance

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How Salty is the Ocean?

• Seawater has a salinity of 35 parts per thousand
  (ppt)
• For every 1000 g of seawater --gt 35 g of salt
• Exactly how salty is 35 ppt?

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Thats a lot of salt . . .

• If salt were removed from ocean and spread evenly
  over earths land surface, it would form a layer
  about 500 feet thick (the height of a 40-story
  office building)
• How do the seas get so salty?
• How did the seas get here in the first place?

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Origin of the Oceans vid clip
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Origin of the Oceans

• 4 bya earth was large, hot rock w/out a trace of
  water
• Outgassing
• Releasing of gasses from mantle through volcanic
  activity
• Comets and meteorites brought gasses as well
• Methane, ammonia, water vapor, carbon dioxide
• 3.8 bya, earths surface cooled below 100C --gt
  water condensed into rain and poured onto land
  for centuries
• Water filled basins and gravity kept it there

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Check with your neighbor about salt

• Where does the salt in the oceans come from?
• Why cant we drink salt water?
• How does a whale, which is a mammal, survive in
  the ocean? Do they drink salt water?
• Show Salty Water video clip (5 min)
• Where does the ocean salt come from?

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The Water Cycle

• Quick review of the water cycle.
• What does this mean?

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Water Cycle

• Rap or Folk song?

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Cleopatra

• Your drinking the same water Cleopatra bathed in
  over 2000 years ago! Yum!
• Par 5 Demo to intro salinity, temperature, and
  density

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Salinity, Temperature, Density Demo

• Density ball demo Is cold water or hot water
  more dense?
• Lets do a demo comparing all three of these
  things . . .
• demo

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Salinity, Temperature, and Density

• Halocline
• A layer of cold, salty water that acts as a
  barrier
• Sea ice forms --gt releases salt --gt denser water
  sinks
• Keeps warmer water from melting ice
• Halocline animation (slow)

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Halocline in cenotes

• Also occurs in cenotes (freshwater caves)
• This is Chak Mool, on the Yukatan peninsula in
  Mexico
• More pics of Chak Mool

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Salinity, Temperature, and Density

• Thermocline
• Layer of water where the temp changes rapidly
• What causes this?
• Solar radiation absorbed and mixed (waves and
  turbulence) evenly in the first 30-40 m
• 90 of total ocean volume is below thermocline
• Avgerage SST?
• 62F
• Average temp of the rest of ocean (below
  thermocline)?
• 32-37 F

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Salinity, Temperature, and Density

• Temp decreases --gt ?
• density increases
• Salinity increases --gt?
• density increases
• Pycnocline
• Layer where there is a rapid change in density

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Bottom Line

• Temp and salinity of seawater determine its
  density It gets denser as it gets saltier,
  colder, or both
• How do scientists get these measurements?

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How do we get this data?

• CTD
• Conductivity-temp-depth meters
• Fig. 3.9 in text
• Red arrow for water samples
• Yellow arrow electronic instruments (temp,
  salinity, light, clarity)
• CTD description

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Dissolved Gases

• How do fish breathe?
• What are they filtering out of the water?
• Dissolved oxygen
• Seawater has dissolved gasses O2, CO2 (80!), N2
• How much O2 in seawater?
• 4-6 ml/l (less than 1)
• In the air we breathe?
• 210 ml/l of air or 21

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Transperency

• Seawater is relatively transparent. Why is this
  so important?
• So photosynthetic organisms can grow
• What colors are in sunlight?
• Do they all travel equal distances?

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True colors

• Fig 3.12 in text at 30m (90ft) only blue light
  remains
• With an electronic flash you see sea stars true
  colors
• Can a plant photosynthesize at this depth if only
  blue light is present?

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Pressure

• At surface, how much pressure?
• Tin can demo
• 1 ATM or 14.7 lbs/in2
• Every 10m (33ft) of increased depth --gt 1 ATM
• How much pressure on a organisms that dives to
  100m?
• 14.7psi x 11 161 psi
• What happens if that organisms surfaces too
  quickly?

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Fig 3.15 in text swim bladder blows up like a
balloon because of decreased pressure.