Chemical%20and%20Physical%20Features%20of%20Seawater

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Chapter 3

• Chemical and Physical Features of Seawater

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Atoms and Elements

• All matter is made of atoms
• There are 118 types of atoms.
• Different types of atoms are elements
• The primary difference in elements is the number
  of protons (atomic number)

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Molecules

• Two or more atoms chemically combined
• Water H20
• Opposite charges
• Oxygen is (-)
• Hydrogen is ()
• Water is a polar molecule

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• Polarity of Water gives it Specific Properties
• Surface tension
• Adhesion
• Cohesion
• Capillarity

hercules.gcsu.edu/.../hydro/slides/capillary.gif
Cohesion molecules stick to same type of
molecule Adhesion molecules stick to other
types of molecules
http//colin.barschel.net/gallery/d/700-4/floating
_paperclip.jpg
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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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Three States of Water

• Solid (ice)
• Liquid
• Gas (steam)

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Fig. 3.2
All particles are in motion. Evaporation occurs
when particles break free of hydrogen bonds at
the surface.
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Fig. 3.3
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Density and State

• As liquid water cools, molecules move slower,
  pack closer together and take less space.
• Density mass / volume
• As liquid water cools, Mass stays the same, but
  volume decreases, so density increases
• When liquid turns to solid, the volume increase
  and density decreases
• Cold water sinks, but ice floats
• Fresh water is densest at 4oC

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Why arent solids densest?

• As liquids cool to solid form, the molecules move
  even less.
• Hydrogen bonds take over and lock molecules into
  a three-dimensional fixed pattern a crystal
• Important oceans dont freeze from the bottom up!

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Energy (heat) is required to break hydrogen bonds.

• Latent heat of melting the amount of heat
  required to melt a substance
• Heat capacity the amount of heat needed to
  raise a substances temperature by a given
  amount.
• One calorie is the amount of energy needed to
  raise one cubic centimeter of water 1oC
• One food Calorie (kcal) is 1000 calories.

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• Latent heat of evaporation the amount of heat
  required to convert a substance from liquid to
  gas.
• Evaporative cooling As faster moving molecules
  escape, the ones left behind have a lower share
  of kinetic energy, so they are cooler!

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Fig. 3.4
As water evaporates, the exposed seaweed shrivels
in the sun.
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Universal Solvent?

• Universal Solvent - A substance that has the
  ability to dissolve both bases and acids, such as
  water.
• Water is sometimes called a universal solvent
  because it is extremely common and dissolves more
  things than any other natural substance.

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Solvents, solutes and solutions.
Solvents dissolve other substances Substances
that are dissolved are solutes. Solvents
solutes solutions
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Fig. 3.5
Dissociation Polar water molecules cluster
around charged atoms, weakening ionic bonds.
Water molecule
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Salts

• Made up of particles with opposite electrical
  charges.
• Ions charged particles
• Either or
• Single atoms or groups of atoms.
• When ions pull apart, or dissociate, salts
  dissolve.

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Salt Composition

• 6 ions compose 99 of the solids dissolved in
  seawater.
• Sodium and chloride make up
• 85 of the solids
• (sodium chloride table salt)

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Salinity

• Salinity the total amount of salt dissolved in
  seawater.
• The number of grams of salt left behind from
  evaporating 100 grams of seawater.
• If 1000 grams of saltwater leaves 35 g salt, the
  water has a salinity of 35 parts per thousand 35
  o/oo
• Practical salinity units(psu) are equivalent to
  parts per thousand

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Rule of Constant Proportion

• The relative amounts of the various ions in
  seawater are always the same.
• ie. Chloride ion is always 55.03
• Water is added by precipitation and removed by
  evaporation or freezing

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Tab 3.1
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Fig. 3.6
Ions in seawater mostly come from weathering,
from hydrothermal vents, or volcanoes releasing
ions into the atmosphere
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Salinity, Temperature and Density

• Sea water density is determined by salinity and
  temperature.
• It gets denser as it gets saltier and colder.

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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

• 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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Fig. 3.7
Niskin bottles are used to sample sea water and
to test temperature
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Fig. 3.8
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Profile

• A profile is a plot that shows temperature,
  salinity, or any other characteristic of seawater
  at various depths in the water column.
• Thermoclines are sudden changes in temperature
  over a small depth interval

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Fig. 3.9
CTDs conductivity temperature depth meters
a rosette of sampling bottles and electronic
instruments
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Dissolved gases

• There are gases dissolved in seawater
• oxygen (O2)
• 0-8 ml/l seawater (air is 21 oxygen)
• carbon dioxide (CO2)
• 80 of the dissolved gas in the ocean (.04 of
  the air)
• nitrogen (N2)
• Gas exchange Gases dissolve into the seawater at
  the surface and are released back
• Gases dissolve better in cold than warm water.

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Fig. 3.12
Transparency is vital for photosynthesis.
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Fig. 3.10
Ocean surface temperature red 29.5oC, 85.1oF
(Arrow at NewGuinea)
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Fig. 3.11
Blue light generally penetrates deepest. Coastal
waters may contain materials that absorb blue
light, making the water appear green.
All light is absorbed by 1,000 meters.
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Fig. 3.13
A Secchi disk measures water clarity
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Pressure
At surface, how much pressure? 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
The internal air sac (swim bladder) of the
longfin grouper.
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Ocean Circulation
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Coriolis effect

• Deflects large-scale motions like wind and
  current to the right in the Northern hemisphere
  and to the left in the Southern Hemisphere.

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Fig. 3.16
Coriolis effect How would an object shot in a
straight line from the North Pole move in
relation to the earth in 2.5 hours? The earth
would rotate under it.
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Wind

• Wind are driven by heat energy from the sun.
• Air is warmer at the equator than the poles.
• warm air is less dense and rises
• adjacent air gets sucked in to replace rising
  equatorial air, creates wind
• winds move and are bent by Coriolis effect
• trade winds approach the equator at 45o angle

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Fig. 3.17
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Fig. 3.18
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Wind Patterns

• What happens to the warm, rising air after it
  releases its moisture?
• It becomes dry and cold and descends towards
  earth N S of equator.
• Where does this happen (in terms of latitude)?
• 30 N and S.
• What type of environment do we usually see here?

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Global Vegetation.
Where are the deserts located?
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Low vs. High Pressure

• Whats the relationship?
• Low pressure
• Hot, moist, rising air
• Clouds and rain
• High Pressure
• Cool, dry, sinking air
• Sunny
• Notice the flow from high to low pressure---This
  is convection!!!
• Explanation (Fig. 7o-3)

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Ekman transport

• Atmospheric winds push the sea surface creating
  currents.
• The upper water layer moves at a 45o angle to the
  wind due to Coriolis effect. (Ekman layer)
• The moving top water layer pushes the layer below
  that moves slower and to the right of the top
  layer (also Coriolis effect.)
• Continues down the water column causing the Ekman
  spiral.

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Fig. 3.19
Net transport is 90o from the wind direction.
Ekman Transport
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Fig. 3.20
Net effect Trade winds move toward the Equator,
but equatorial currents move parallel to the
Equator This forms large circular systems called
gyres
Water currents bring warm water to poles, cool
water to tropics to regulate the Earths climate.
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Fig. 3.21
Tropical organisms prefer high latitudes on west
sides of oceans. Kelp (cold-loving) occur closer
to the Equator near Eastern shores of oceans
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Fig. 3.24
3-layered Ocean
stratified in layers or strata
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The 3-layered ocean

• Surface layer (or mixed layer)
• mixed by wind, waves, and currents
• 100-200 m thick
• may have sharp transitions to cooler water below
  (seasonal thermoclines)
• Intermediate layer to a depth of 1,000 to 1,500
  m.
• main thermocline is in the intermediate layer
• rarely breaks down
• feature of the open ocean
• Deep and bottom layers are below 1,500m
• Uniformly cold, less than 4oC

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Fig. 3.22
TYPICAL OPEN OCEAN PROFILES
b. temperature varies with latitude c. seasonal
thermoclines develop during the summer
Variation at the surface due to evaporation,
precipitation, and runoff.
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Fig. 3.23
A high density difference results in a stable
water column.
Surface water may become more dense and less
energy is needed to mix with water below.
Downwelling occurs when the upper layers becomes
denser and displaces and mixes with deeper water.
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Overturn

• When surface water downwells, becoming denser
  than water below.
• Surface water sinks, displacing lower water.
• Occurs in temperate and polar regions during the
  winter when the surface cools.

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Water Mass

• Once surface water sinks, it maintains its
  salinity and temperature.
• That volume of water (the water mass) has a
  fingerprint or characteristic identification
  based on salinity and temperature.
• Oceanographers follow the movement of the water
  mass circulation
• Thermohaline circulation density driven
  circulation (thus saline and temperature driven)

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Fig. 3.25
Global thermohaline circulation critical in
regulating the Earths climate
The Great Ocean Conveyor starts with cold, salty
water in Greenland sinking and spreading.
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Waves

• Crest
• Highest point
• Trough
• Lowest point
• Wavelength
• Distance between crests
• Period
• Average time interval (seconds) between
  successive crests or troughs of a wave

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Fig. 3.27
Waves move energy, but not matter. The water
moves in circles, up with the crest, and down
with the trough.
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• The size of waves depends on
• Speed of wind
• Length of time wind blows
• Fetch
• Span of open water over which wind blows

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Fig. 3.29
Seas Wind pushes wave crests into sharp peaks
and stretches out troughs. Swells Away from the
wind, waves settle into swells with smoothly
rounded crests and troughs.
Surf near the shore, the bottom forces the water
into elongated ellipses, slowing the wave. Waves
pile up getting higher and steeper. High and
steep enough to fall forward and break surf
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Waves entering shallow water

• Wave feels ocean bottom --gt friction --gt 3 things
  happen
• Wave speed decreases
• Wavelength decreases
• Wave height increases
• Whats this called?

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• Wave cancellation when one wave crest lines up
  with another wave trough
• Wave reinforcement multiple waves line up crest
  to crest.
• creates rogue waves that may be as high as a
  ten story building

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Tides

• The combined effect of the gravitational pull of
  the moon and sun and the rotation of the earth,
  moon and sun.
• Centrifugal force arises because the moon doesnt
  rotate evenly around the center of the earth.
• rotates around the earth/moon center of mass.

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Fig. 3.30
Grunion spawn with the peak of the highest tide.
The fish climb to the highest part of the beach.
Eggs hatch a month later. High tides help the
young swim away.
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Fig. 3.31
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Tides Bulges

• Why the bulge on the side opposite of the moon?
• Centrifugal force
• Caused by earth and moon system rotating around
  common center of mass
• You have two bulges (high tide)
• Whats happening at the other two places?
• Low tide!

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Tides Spinning

• Because the earth spins, the place where high and
  low tides occur are constantly changing
• Notice the red flag
• About every 6 hours

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Tides Spring and Neap

• When are tidal bulges the largest?
• When sun and moon are in line, acting
  togetherspring tides

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Tides Types

• Semidiurnal two high, two low
• Mixed semidiurnal successive high tides of
  different height
• Diurnal one high and one low

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Tides Vary

• Based on continents, islands and bottom
  topography
• Continents block westward passage of tidal bulges

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Tidal Bores

• A high wave caused by an extreme incoming tidal
  flow
• Shape of estuary must be shallow and uniform
• Only occur in about 100 rivers in the world

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Bering Sea Current Patterns
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