Chemical and Physical Features of Sea Water and the World Ocean

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Chemical and Physical Features of Sea Water and
the World Ocean

• Chapter 3

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The Waters of the Ocean

• Earth is the only planet with liquid water.
• Marine organisms cannot control the physical and
  chemical nature of their environment so they have
  to grin and bear it.
• Organisms must adapt, live somewhere else, or
  die.
• Marine organisms consist of mostly water. Most
  are 80 water. Jellyfish are 95 water!

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The Unique Nature of Pure Water

• Lets take a minute to review
• Atoms
• Molecules
• Hydrogen bonds
• Water is made of two hydrogen atoms bound to an
  oxygen atom by two hydrogen bonds.

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The Three States of Water

• Any substance can exist in three different
  states/phases
• Solid
• Liquid
• Gas
• Water is the only substance that naturally
  occurs in all three states on earth.

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Liquid Water

• Liquid water is held together by Hydrogen bonds.
  These bonds move, so they break and reform
  constantly.
• Temperature reflects the average speed of water.
  The higher the temperature the faster the water
  molecules are moving.
• When water molecules move fast enough and break
  free of hydrogen bonds it escapes to the
  gas/vapor phase. This process is called
  evaporation.

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Water Vapor

• Water vapor molecules are not held together by
  hydrogen bonds. They are separate and much
  farther apart.
• As temperature increases the rate of evaporation
  increases.
• Water boils at 100C (212F) when nearly all the
  hydrogen bonds are broken and the molecules enter
  the vapor state.

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Solid Water

• When liquid water cools, molecules move slower
  and pack closer together to take up less space.
• When the temperature of water decreases the
  volume of water decreases without changing the
  mass, so the water gets denser.
• Remember Dm/V

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Seawater

• As seawater gets colder, it gets more dense and
  sinks.

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Freshwater

• As freshwater gets colder, it becomes less dense
  and floats.
• That is why a sheet of ice can cover the top of a
  lake or pond allowing aquatic life to remain
  alive below.

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Water Crystals

• Crystals form when water molecules move slowly
  and the hydrogen bonds lock in a 3-D pattern.
• Ice crystals have molecules that are farther
  apart than liquid water.
• Ice expands as it freezes.

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Heat and Water

• Ice is held with hydrogen bonds.
• These bonds must be broken for ice to melt.
• Ice melts at a much higher temperature than
  similar substances.
• If not for the hydrogen bonds ice would melt at
  -90C (-130F) instead of 0C (32F)!

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• Water absorbs a lot of heat when it melts.
• The Latent Heat of Melting- is the amount of heat
  to melt a substance.
• Water has a higher latent heat of melting than
  any other common substance.
• A GREAT deal of heat must be removed to freeze
  water. It takes a long time before complete
  body of water will freeze solid!

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Drinks stay cold because any heat goes to melting
the ICE, not raising the temperature of the drink.
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Heat Capacity

• Is the amount of heat need to raise a substances
  temperature by a given amount.
• Water has one of the highest heat capacities.
• It can absorb a lot of heat and raise the
  temperature very little.
• This provides for utility as a coolant for
  automobiles and allows marine life not to be
  subject to rapid changes in heating and cooling
  of their habitats.

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Latent Heat of Evaporation

• Ability of water to absorb a great deal of heat
  when it evaporates.
• Evaporative cooling- when the fastest molecules
  leave the liquid phase take heat with them and
  those left behind on the organism, such as human
  skin, lower our body temperature.

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Water as a Solvent

• Water can dissolve many more things than any
  other natural substance.
• Ex Salts- which are made of ions.
• Na Cl-
• Salt crystals in water attract water molecules
  with their charges like magnets. The ions
  dissociate (pull apart) and dissolve.

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Seawater Composition

• Seawater is composed of particles that are
  dissolved in the water by different means.
• Weathering- produces some of the solids that are
  found in seawater.
• Hydrothermal vents- release sediments into
  seawater from underwater geothermal activity.

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Salt Composition- made of mostly 6 ions in 99 of
seawater.
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• Sodium chloride accounts for 85 of the solids in
  seawater.
• When seawater evaporates salts are left behind.
• Salinity- is the total amount of salt dissolved
  in seawater.
• Ex If 35g of salt are left from 1000g of
  seawater evaporation then the seawaters salinity
  is 35.
• Salinity is measured today with electrodes
  because salts are wonderful conductors.

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Practical Salinity Units (psu)

• Units of salinity from conductivity measurements.
• Why is this important?
• The degree of salinity affects organisms.
• Not just the total amount of salt is important,
  but also the composition of the salt.
• Some organisms may tolerate NaCl, while
  withstanding KCl.

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• Chemist William Dittmar analyzed water samples
  from the Challenger and found that the major ions
  in seawater remained constant even though the
  total amount varied from place to place.
• For example, Cl was always at 55.03.
• This finding led to The Rule of Constant
  Proportion.

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• Water is removed from the ocean primarily by
  evaporation.
• When the water freezes the ions in the water do
  not freeze so frozen seawater becomes fresh!
• This frozen water makes up the polar ice caps.
• The salinity of the water surrounding the ice
  caps is very saline because of these remaining
  ions in the seawater.

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• Water is added to the seas by precipitation and
  on a small scale glacial melting.
• The average ocean salinity is 35. Most seawater
  varies between 33-37.
• The Red Sea has high evaporation and is 40
  saline.
• The Baltic Sea has a great deal of runoff from
  fresh water sources and is 7 saline.

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Salinity/Temperature/Density

• Temperature affects density.
• The greater the temperature of the seawater the
  more dense is so it?
• Salinity affects density.
• The saltier the seawater the more dense the water
  is so it?

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• Temperature in the open water varies from
• -2C to 30C (28F-86F).
• In seawater temperatures can occur below 0C (32F)
  because seawater freezes at a cooler temperature.
• This makes the ocean less prone to freeze then
  lakes and rivers.

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• Temperature in the ocean is measured with
  specially designed bottles and thermometers
  lowered to a desired depth.
• Temperature Profiles- graphs generated from
  temperatures taken at different depths.
• They reflect a water column- vertical column of
  temperatures of water at their respective depth.

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Temperature Profiles of Ocean
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Tools for data collection.

• Researchers can also plot salinity or density at
  different depths using different probes.
• Today CIDs are used to measure- Conductivity,
  Temperature, and Depth of ocean water.
• Bathythermographs (XBTs) are used to measure
  temperature and are disposable.
• Niksin bottles collect individual water sample
  from different depths.
• Satellites measure conditions near the surface
  instantaneously.

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Dissolved Gases in Water

• The most important gases in seawater are
• Oxygen
• Carbon Dioxide
• Nitrogen
• These gases are dissolved in the water from the
  atmosphere into the surface seawater and are
  released back into the atmosphere through
  evaporation (gas exchange.)

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Water Cycle
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• Gases dissolve better in cold water.
• There are more dissolved gases found in polar
  waters.
• Oxygen gas is not very soluble only 0-8ml of
  oxygen will dissolve in 1L of seawater. Usually
  about 4-6ml.
• In the atmosphere there is about 210ml of oxygen
  in 1L air.

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Photosynthesis/Respiration

• Photosynthesis and respiration affect the amount
  of dissolved oxygen in seawater.
• Most of the oxygen produced in the ocean is by
  photosynthesizing organisms that release oxygen
  into the atmosphere as a product of this process.
• Seawater has little dissolved oxygen.

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• Carbon dioxide is much more soluble.
• It makes up 80 of the dissolved gas in the ocean
  and stores 50 times as much CO2 as the
  atmosphere!
• This makes the ocean a critical component to
  controlling the greenhouse effect by absorbing a
  great deal of greenhouse gases that could be in
  the atmosphere increasing global

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Transparency

• Water is transparent
• This is the ability for light to penetrate the
  water and allows photosynthetic organisms to
  grow.
• Remember, sunlight has all the colors of the
  rainbow, and not all colors are going to
  penetrate equally.
• Clear ocean water is most transparent to blue.
• Transparency can be affected by large quantities
  of plankton (algae). They reduce transmittance
  of light from the surface.

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Color Transparency of Ocean Water