Physical

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Chapter 3

• Physical Chemical Features of Seawater the
  World Ocean

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Earth The Water Planet

• Water covers about 71 of the Earths surface,
  yet the vast majority cannot be used for
  drinking, irrigation, or industry because it is
  salt water.
• As the worlds population increases, so does the
  need for water part of the solution to meeting
  this demand lies in understanding what water is,
  where it goes, how it cycles through nature.

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Earth The Water Planet

• Water travels in a hydrologic cycle, changing
  form as organisms take it in, as it evaporates,
  as it condenses, as it flows from one location
  to another.
• Scientists believe that the water we drink today
  is billions of years old.

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Waters Structure

• Compared to many important molecules, water is a
  simple molecule (a group of atoms held together
  by chemical bonds).
• It consists of three atoms two hydrogen (H)
  one oxygen (O).
• H2O

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Waters Structure

• The atoms of a water molecule are held together
  by covalent bonds (formed by atoms sharing
  electrons).
• The oxygen atom shares the electrons of two
  single-electron hydrogen atoms.

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Waters Structure

• Water is a polar molecule (A molecule with
  positive negative ends has polarity is called
  a polar molecule).
• The two hydrogen atoms have a net positive
  charge.
• The oxygen atom has a net negative charge.

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Waters Structure
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Waters Structure

• The water molecules polarity allows it to bond
  with adjacent water molecules.
• The positively charged hydrogen end of one water
  molecule attracts the negatively charged oxygen
  end of another water molecule (Remember
  opposites attract).
• The bonds between adjacent water molecules are
  called hydrogen bonds.
• Individual hydrogen bonds are weak compared to
  covalent bonds (only 6 as strong) therefore
  easily break reform however, they are strong
  enough to give water its unique properties.

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Waters Structure
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Waters Unique Properties
Physical Properties of Water
Boiling Point 100o C
Freezing Point 0o C
Heat Capacity 1.00 cal/g/oC
Density (at 4o C) 1.00 g/cm3
Latent Heat of Fusion 80 cal
Latent Heat of Vaporization 540 cal
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Waters Unique Properties

• Water is the only naturally occurring substance
  that exists in all three phases solid, liquid,
  gas.
• The most important characteristic of hydrogen
  bonding is the ability for water to exist as a
  liquid at room temperature.
• Without hydrogen bonds, water would exist as a
  gas at room temperature ? a steam planet instead
  of a liquid planet.

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Waters Unique Properties

• Because hydrogen bonds attract water molecules to
  each other, water molecules tend to stick
  together ? cohesion.
• Cohesion gives water a more organized structure
  than most liquids.

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Waters Unique Properties

• Water also sticks to other materials due to its
  polar nature ? adhesion.
• An example of this is the tendency for a drop of
  water to cling to a humans skin.
• Adhesion also accounts for capillary action (the
  ability of water to rise in narrow spaces, such
  as a straw or tube).

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Waters Unique Properties

• Surface Tension a skin-like surface formed due
  to the polar nature of water.
• AKA waters resistance to objects attempting to
  penetrate its surface.
• Caused by cohesion.
• To small creatures (i.e. water strider) surface
  tension is a strong force, allowing them to
  literally stand on water.
• Neuston (plankton that live on the waters
  surface) rest on surface tension rather than
  float.

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Waters Unique Properties
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Waters Unique Properties

• Viscosity the tendency for a fluid (gas or
  liquid) to resist flow.
• Most fluids change viscosity as temperatures
  change.
• The colder water gets, the more viscous it
  becomes. Therefore
• It takes more energy for organisms to move
  through cold water than warm water.
• Drifting organisms use less energy to keep from
  sinking in cold water than warm water.

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Waters Unique Properties

• Cold water holds more oxygen than the same volume
  of warm water, so..
• organisms can survive at the ocean floor.
• Cold water is also denser than warm water, which
  means it weighs more per unit volume of water,
  so..
• colder water sinks beneath warmer water.
• Even though colder water is more dense than
  warmer water, this changes when the water gets
  cold enough to freeze.

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Waters Unique Properties

• As water cools, the molecules not only move
  slower, they pack closer together take up less
  space, so that the volume of water decreases, but
  only down to a temperature of 3.98o C.
• At 4o C water expands as it freezes.
• Because the same mass of water occupies more
  volume as ice than as liquid water, ice is less
  dense floats.

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Waters Unique Properties

• Ice Floats
• The space occupied by 24 water molecules in the
  solid state could be occupied by 27 molecules in
  the liquid state (water expands 9 as it freezes).

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Waters Unique Properties

• If ice did not float
• a body of water would freeze from the bottom up
  eventually the whole body of water would freeze.
• aquatic organisms would not survive (a floating
  layer leaves water below, where organisms can
  live, insulates it so it doesnt freeze).
• the Earths climate would be colder perhaps too
  cold for life.

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Waters Unique Properties

• Water has a high latent heat of melting, which
  means that ice melts at relatively high
  temperatures absorbs a great deal of heat as it
  melts.
• Water has the highest latent heat of evaporation
  (the amount of heat required for a substance to
  evaporate) of any naturally occurring substance.

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Waters Unique Properties

• Water has a high heat capacity (the amount of
  heat required to raise a given amount of a
  substance by a given temperature).
• Heat capacity is measured in calories per gram.
• The heat capacity for water is 1 calorie per
  gram.

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Waters Unique Properties

• It takes more heat energy to raise waters
  temperature than that of most other substances
  therefore, water can absorb or release a lot of
  heat with little temperature change.
• Waters heat capacity affects the worlds climate
  weather. Seawater acts as a global thermostat
  - heat is carried to areas of the world that
  would otherwise be cooler, heat is absorbed in
  areas that would otherwise be hotter.

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Waters Unique Properties

• This high heat capacity is great for marine
  organisms because it means that they are not
  subject to the wide temperature ranges often seen
  on land, except in shallow water, which warms up
  quickly due to the small volume of water.

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Waters Unique Properties

• Water is a powerful solvent.
• Solvent usually a liquid the more abundant
  component in a solution
• Solute often a solid or gas the less abundant
  component in a solution
• Solution made of two components, with uniform
  molecular properties throughout

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Waters Unique Properties

• Water (solvent) dissolves salt (solute)
• Waters charged ends pull apart (dissociate) a
  salt (i.e. sodium chloride, the primary solutes
  in the ocean, which give it a salty taste)
  crystal.
• Sodium chlorine become charged particles
  ions.
• The positive sodium ion is attracted to the
  negative side of the water molecule.
• The negative chlorine ion is attracted to the
  positive hydrogen side of the water molecule.

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Waters Unique Properties

• Sodium Chloride Molecule (sodium chlorine ions)

• Sodium Chloride Dissociating in Water

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Composition of Seawater

• Most salts found in seawater are present in their
  ionic form.
• 6 ions make up 99 of the dissolved salts in the
  ocean.
• Trace ions make up the other 1.

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Composition of Seawater
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Composition of Seawater
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Composition of Seawater

• Sea salt originated from Earths crust.
• Ions are added to seawater by
• rivers running off crustal rocks
• volcanic activity
• groundwater
• hydrothermal vents cold springs
• the decay of once living organisms

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Composition of Seawater

• Ions are removed from the ocean by
• chemical entrapment as water percolates through
  the mid-ocean ridge systems seamounts
• sea spray
• uptake by living organisms
• incorporation into sediments
• subduction
• evaporites (salt deposits)

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Composition of Seawater

• The average length of time an element spends in
  the ocean is known as its residence time
• Conservative constituents are those that occur in
  constant proportions have the longest residence
  times (i.e. the most abundant dissolved materials
  in the ocean).
• Non-conservative constituents are usually
  associated with seasonal, biological, or short
  geological cycles have short residence times.

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Composition of Seawater
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Composition of Seawater

• Salinity the total quantity of all dissolved
  inorganic solids (ions) in seawater.
• Expressed in g per kg water or parts per thousand
  (o/oo)
• Average salinity is 35 o/oo, which means that for
  every 1000 grams of water there are 35 grams of
  salt.

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Composition of Seawater

• Salinity of surface water varies as a result of
  evaporation, precipitation, freezing, thawing,
  freshwater runoff from the land.
• Between 10o N 10o S of the equator, salinity is
  low due to heavy rainfall.
• At 30o N 30o S, salinity is high because
  evaporation gt precipitation.
• At 50o N S, salinity is low due to heavy
  rainfall.
• At the poles, salinity is high because freezing
  removes water from the ocean.

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Composition of Seawater

• In seawater, no matter how much salinity varies,
  the proportions of several key inorganic elements
  compounds (dissolved salts only) do not change.
  Only the amount of water salinity changes.
• This constant relationship of proportions in
  seawater is known as the Law of Constant
  Proportions.

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Composition of Seawater

• If a scientist knows how much of any one seawater
  chemical he/she has, salinity can be determined
  using the Law of Constant Proportions
• Chloride ions account for 55 of dissolved
  solids - determining a samples chlorinity is
  relatively easy.
• The formula for determining salinity is based on
  chlorinity
• Salinity in o/oo 1.80655 x Chlorinity in o/oo

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Composition of Seawater

• Is the ocean becoming progressively saltier with
  age?
• No, the ocean is in chemical equilibrium ions
  are being added to removed from the ocean at
  the same rate.

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Composition of Seawater
Gases Found in Seawater
Gas by Volume in by Volume in by Volume in Atmosphere Surface Seawater Ocean Total
Nitrogen 78.08 48 11
Oxygen 20.99 36 6
Carbon Dioxide 0.03 15 83
Other Gases 0.95 1
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Composition of Seawater

• Gases in Seawater
• Gases from biological processes
• O2 is a by-product of photosynthesis
• C02 is a by-product of respiration
• Solubility of gases in seawater
• Seawater has more O2 CO2 but less N2 than the
  atmosphere
• Relative solubility of gases in seawater
• CO2 gt O2 gt N2
• Affected by temperature, salinity, pressure.

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Composition of Seawater

• Gas Concentrations Vary with Depth
• O2 is abundant near the surface because of
  photosynthetic activity of marine organisms.
• O2 concentration decreases below the sunlit layer
  because of the respiration of marine animals
  bacteria, because of the O2 consumed by the
  decay of tiny dead organisms slowly sinking
  towards the bottom.

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Composition of Seawater

• In contrast, because plants use CO2 during
  photosynthesis, surface levels of CO2 are low.
• Because photosynthesis cannot take place in the
  dark, CO2 given given off by animals bacteria
  tends to build up at depths blow the sunlit
  layer. CO2 also increases with depth because its
  solubility increases as pressure increases
  temperature decreases.

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Composition of Seawater

• An acid is a substance that releases a hydrogen
  ion in solution.
• A base is a substance that combines with a
  hydrogen ion in solution.
• Acidity alkalinity is measured on a pH scale
• 0-6.9 acids
• 7 neutral
• 7.1-14 bases
• Seawater has an average pH of 8, making it
  slightly basic.

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Composition of Seawater

• The oceans acid-base balance varies with
  dissolved components depth.

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Colligative Properties of Seawater

• Colligative properties properties of a liquid
  that may be altered by the presence of a solute
  are associated primarily with seawater.
• Pure water does not have colligative properties.
• The strength of the colligative properties
  depends on the quantity of solutes.

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Colligative Properties of Seawater

• Raised boiling point Seawater boils at a higher
  temperature than pure water.
• Decreased freezing point As salinity increases,
  water resists freezing (why salt is put on a road
  during ice/snow storms).
• Decreased heat capacity It takes less heat to
  raise the temperature of seawater.

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Colligative Properties of Seawater

• Electrically Conducive Seawater has the ability
  to conduct an electrical current.
• Slowed evaporation Seawater evaporates more
  slowly than fresh water due to the attraction
  between ions water molecules.

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Salinity, Temperature, Water Density

• Waters density (the mass of a substance in a
  given volume, usually measured in g/cm3) is the
  result of its temperature salinity
  characteristics
• Density of pure water 1 g/cm3
• Density of seawater 1.0270 g/cm3
• Density increases when salinity increases.
• Density increases when temperature decreases.

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Salinity, Temperature, Water Density
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Salinity, Temperature, Water Density

• Density differences cause water to separate into
  layers. High-density water lies beneath
  low-density water.
• Low temperature high salinity are features of
  high-density water.
• Relatively warm, low-density surface waters are
  separated from cool, high-density deep waters by
  the thermocline the zone in which temperature
  changes rapidly with depth.

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Salinity, Temperature, Water Density

• Salinity differences overlap temperature
  differences. The transition from low-salinity
  surface water to high-salinity deep water is
  known as the halocline.
• The thermocline halocline together make the
  pycnocline the zone in which density increases
  with increasing depth.

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Salinity, Temperature, Water Density

• The ocean is divided into 3 density layers
• Surface zone the upper layer of the ocean
  extends to about 100 m accounts for only 2 of
  the total ocean volume
• Pycnocline needs only a temperature or salinity
  difference to exist contains 18 of all ocean
  water
• Deep zone there is little change in density
  throughout this layer deeper than 1,000 m in the
  middle latitudes contains 80 of all ocean
  water

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Light

• Water scatters (occurs when light is bounced
  between air water molecules, dust, other
  objects) absorbs (occurs when lights
  electromagnetic energy is converted to heat in
  the molecules of seawater) light.

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Light

• When water reaches waters surface, some light
  penetrates, but, depending on the suns angle,
  some is reflected back into the atmosphere.
• Light-colored suspended particles reflect light.
• Dark-colored suspended particles algae absorb
  light.
• Water molecules absorb the energy, converting
  light into heat.

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Light

• Water absorbs colors at the red end of the
  spectrum more easily than at the blue end.
• The first meter of water absorbs nearly all the
  infrared light.
• The color red is almost totally absorbed at 4
  meters.
• As light passes through more water, orange is
  almost completely absorbed next, followed by
  yellow, green, blue, indigo, violet.
• Blue is the strongest color travels through
  most of the water before its completely
  absorbed, which explains why very clear water
  appears blue.

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Light

• How deeply light penetrates depends on how clear
  or turbid (cloudy) the water is.
• In coastal areas with lots of runoff, penetration
  may be limited to lt 3 meters.
• In the clearest water, a spectrophotometer may
  detect light as deep as 590 meters however,
  significant light penetration is limited to 100
  meters.

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Light

• Two zones exist with respect to light
  penetration
• Photic zone where light penetrates can be as
  deep as 600 meters has two subzones
• Euphotic zone the upper shallow portion where
  most biological production occurs comprises
  about 1 of the ocean
• Dysphotic zone where light reaches, but not
  enough for photosynthetic life.
• Aphotic zone where light does not reach only
  a fraction of marine organisms live makes up the
  vast majority of the ocean

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Light
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Sound

• Sound travels well in air, but even better in
  water.
• In distilled water at 20o C, sound travels
  1,482.4 m/s, which is 5 times faster than it
  travels in air.
• Sound travels through warm water faster than cool
  water, but travels faster in deep water due to
  pressure.

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Sound

• Sound

• The relationship between water depth the speed
  of sound.

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Sound

• Sound bounces off suspended particles, water
  layers, the bottom, other obstacles, is
  eventually absorbed by water as heat.
• Refraction causes SOFAR layers shadow zones.
• The SOFAR layer is one in which sound waves
  travel at minimum speed.
• Sound transmission is particularly efficient
  (sounds can be heard for great distances) because
  refraction tends to keep sound waves within the
  layer.

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Sound

• The SOFAR layer in which sound waves travel at
  minimum speed sound transmission is efficient.

• The shadow zone, a thin, high-sound-velocity
  layer, which forms at 80 meters deflects sound.

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Sound

• Because sound travels so well in water, marine
  mammals use echolocation to sense an objects
  size, distance, density, position under water.

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Pressure

• Pressure exerted by water is called hydrostatic
  pressure (the weight of the water column above a
  given depth).
• At sea level, atmospheric pressure 1 bar.
• At 10 meters below sea level, total pressure 2
  bars (1 bar from atmospheric pressure plus 1 bar
  from hydrostatic pressure). A marine organism
  living at 10 m experiences twice the pressure
  present at sea level.
• Pressure increases 1 bar for each additional 10 m
  (i.e. at 30 m, the pressure is 4 bars).

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Pressure
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Pressure

• Many fish have a gas bladder that they use to
  control their buoyancy (an upward force equal to
  the weight of the gas or liquid displaced).
• Fish must add or release gas from the bladders
  when they change depth to keep the pressure in
  balance.
• Scuba divers learn to add space in their ears
  (equalizing), which allows them to dive without
  discomfort.

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Pressure
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Buoyancy

• Water is far denser than air (about 800 times),
  so buoyancy in water is a significant force.
• This means that most organisms in water are
  buoyed up by a force nearly the same as their own
  weight.

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Buoyancy
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Buoyancy

• Some living tissue organic structures like
  bone, teeth, shells, have a greater density
  than water therefore sink. Organisms have
  various adaptations to handle this
• Gas bladders
• Light skeletons
• Tissue high in oil
• Production of ammonium chloride, which is less
  dense than seawater.

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Buoyancy

• Large shell-bearing invertebrates live on the
  bottom.
• Planktonic organisms store food as lightweight
  waxes oils.
• Because of buoyancy, marine organisms dont have
  to expend much energy to offset their own weight
  compared to land-based existence.
• This allows entire communities to exist simply by
  drifting.

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Buoyancy

• It allows many swimming creatures to live most of
  their lives without ever coming in contact with
  the bottom.
• It allows organisms to grow larger than those on
  land (i.e. blue whale)