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Chap 6 Water & Ocean Structure

    Physical Oceanography
Water and Heat
 Sun is exclusive
  source of energy
  driving ocean and
  atmospheric currents.
 The Sun radiates
  throughout the
  electromagnetic
  spectrum, but principle
  radiation is in visible
  part of the spectrum.
 Visible light is strongly
  absorbed by seawater
 Heat  – energy produced by random
  vibration of atoms or molecules.
 Temperature – object’s response to
  an input or removal of heat.
 Specific heat – heat required to
  raise the temperature of 1 g of
  substance by 1 °C. (calories / g)
Infrared Energy
 in clear water, only
  10% reaches 25 m,
  only 0.5% reaches
  100 m, .0025%
  reaches 200 m
 essentially all
  energy gain in the
  oceans takes place
  in upper 10 -100 m
  of water
Concept of Steady State

 Averaged   over the globe and over
  a year, the Earth loses as much
  energy as it gains.
 Green house effect may be
  changing the steady state
 There is a net gain of energy at low latitudes
  and a net loss of energy at high latitudes.
 This latitudinal difference is energy gain and
  loss drives both ocean and atmospheric
  circulation.
 All energy exchange by the oceans occurs at
  the surface
 This exchange of energy controls the
  temperature of ocean water masses
Density
 Mass   / volume (g / cm3)
 Density depends on temperature and
  salinity
 Ocean density ranges from 1.02 to 1.03
  g/cc.
 Density differences, together with
  winds, are the principal factors
  determining ocean currents.
Freezing Water
 Density  curve (6.6) shows the
 relationship between the temperature or
 salinity of a substance and its density.
Chapt 6 water & ocean structure
 Water density decreases as the water
  freezes
 Angle between water molecules expand
  from 105 ° to 109 °
 Forms a crystalline lattice – less dense,
  hence ice float.
 Sensible heat loss – detectable decrease in
  heat, measured with a thermometer, before
  ice freezes
 Latent [hidden] heat of fusion – amount of
  heat removed to form ice per g of water (80
  calories)
 This process of freezing and thawing
  moderates global temperature swings. Why?
Review the Concepts
 Heat  is transmitted in the ocean in
  which wave length?
 Define density
 The density of a parcel of seawater will
  be affected by which factors
Evaporating Water
 Latent
       heat of evaporation – amount of
 energy required to break hydrogen
 bonds
 585  cal / g at 20 °C
 Why such a big difference between
  latent heat of evaporation and the latent
  heat of fusion?
Sea Water vs. Pure Water
 Solids dissolved          No solids, water
  lowers specific heat       requires 1 cal to
  by 4% (heats faster)       heat up vs. 0.96 cal
 Ions also interfere        sea water.
  with the freezing         No ions to interfere
  point, the saltier the     with the freezing
  lower the freezing         point
  point
Chapt 6 water & ocean structure
Solar Energy Inputs
 the sun 'makes a direct hit' at equator, while
  the same sunlight is spread over a larger area
  at the poles.
 This is just another way of showing that the
  equator is heated up more than the north or
  south poles of the Earth.
 This uneven heating of our round globe
  causes the air at the equator to rise, cool, and
  then wring out its moisture as rain.
Chapt 6 water & ocean structure
 The    equator, then, is a zone of low
  pressure systems and lots of
  rainfall.
 This zone extends from roughly 5°N to
  5°S of the equator.
 The air doesn't keep rising forever.
 It eventually reaches an altitude where
  it is the same temperature (and density)
  as the surrounding air.
 Itthen spreads out laterally, both in a
  north direction, and in a south direction.
 As it moves poleward (either north or
  south from the equator), the air
  continues to cool, and finally, sinks.
  Where it sinks, the pressure is high.
 Heat budget is balance (p.163, f. 7.10)
Chapt 6 water & ocean structure
Density Structure of the Ocean
 Winds are the primary driving force of the
  surface circulation, which is also called wind-
  driven circulation,
 density differences drive the deep, or vertical,
  circulation of the oceans.
 The density of seawater is controlled by
  temperature and salinity, so the deep
  circulation is also called the thermohaline
  circulation.
Review the Concepts
 Contrastsea water and fresh water
 What causes the seasonal changes?
 Why the poles are cold?
 Temperature differences as small as a few
  hundredths of a degree and salinity
  differences of a few parts
 in a hundred thousand can be important.
 Both temperature and salinity are
  conservative properties of seawater, that is,
  there are determined by processes occurring
  at the surface.
Salinity
 Salinity  refers to the weight fraction of
  dissolved solids in water.
 Average salinity of seawater is about
  35‰ (‰ and ppt mean “parts per
  thousand).
 Principal processes that change salinity
  are:
 1. dilution (by rainwater and river water)
 2. Evaporation freezing (& thawing)
  of sea ice
 Salinity changes occur only at the
  surface of the ocean
 Because   temperature and salinity
  change only at the surface density
  changes occur only at surface
 Water masses can be identified by their
  temperature-salinity characteristics.
 Density, together with winds, govern
  ocean currents
Ocean Structure
 Upper 100-500 m to have uniform
  temperature and salinity because of
  mixing by waves.(6.13)
 Below this, to a depth of ~1000 m,
  Temp., Salinity, and density change
  ( Thermocline, Halocline,
  Pycnocline) (6.12)
Chapt 6 water & ocean structure
 Indeep water, temperature, salinity and
  density are relatively uniform
 This structure varies latitudinally. At
  mid-latitudes, it also varies seasonally:
  upper mixed layer will deepen in
  summer;
 thermocline might largely disappear in
  winter
Chapt 6 water & ocean structure
Sound
 Is a form of energy transmitted by rapid
  pressure changes in an elastic medium.
 Intensity decreases as it travels through
  seawater until eventually is absorbed
  and converted into heat
 Speed is 1,500 m / s, almost five time
  the speed in air
Echolocation
 Marine mammals use
  sound rather than light
  to “see” in the ocean
 Echolocation –use of
  reflected sound to
  detect environmental
  objects
 MM use echolocation
  to detect prey and
  avoid obstacles
 Speed of sound increases as temperature
  and pressure increases (6.21)
 Travels faster at the surface than in deeper,
  cooler water.
 Minimum speed at 600 – 1,200 m
 Below this depth the pressure offsets the
  temperature and speed increases again
Chapt 6 water & ocean structure
SOFAR Layer
 Sound Fixing and Ranging
 Transmission of sound in this minimum-
  velocity layer is very efficient because
  refraction tends to cause sound energy to
  remain within the layer (6.20)
 Loud sounds made at this depth can be
  heard for thousands of kilometers
 Sound generated in the India Ocean was
  hear as far a way as the Oregon Coast (Box
  6.1)
Chapt 6 water & ocean structure
SONAR
 Sound  Navigation and Ranging
 Active SONAR – projection of short
  pulses of high frequency sound to
  search for objects in the ocean.
 Operator can tell direction, size,
  heading and even the composition by
  analyzing the composition of the
  returned ping
Chapt 6 water & ocean structure
 Side-Scan  Sonar – towed behind a
  vessel (6.22)
 Used for geological and archeological
  studies, and the location of downed
  ships and airplanes
Review the Concepts
 What kind of temperature does most of the
  world ocean has?
 What is characteristic about the ocean's deep
  sound channel (sofar layer) ?
 What is called a zone in which the ocean's
  salinity increases rapidly with increasing
  depth?
 Which zone does the most pronounced or
  marked all year around thermoclines exist?

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Chapt 6 water & ocean structure

  • 1. Chap 6 Water & Ocean Structure Physical Oceanography
  • 2. Water and Heat  Sun is exclusive source of energy driving ocean and atmospheric currents.  The Sun radiates throughout the electromagnetic spectrum, but principle radiation is in visible part of the spectrum.  Visible light is strongly absorbed by seawater
  • 3.  Heat – energy produced by random vibration of atoms or molecules.  Temperature – object’s response to an input or removal of heat.  Specific heat – heat required to raise the temperature of 1 g of substance by 1 °C. (calories / g)
  • 4. Infrared Energy  in clear water, only 10% reaches 25 m, only 0.5% reaches 100 m, .0025% reaches 200 m  essentially all energy gain in the oceans takes place in upper 10 -100 m of water
  • 5. Concept of Steady State  Averaged over the globe and over a year, the Earth loses as much energy as it gains.  Green house effect may be changing the steady state
  • 6.  There is a net gain of energy at low latitudes and a net loss of energy at high latitudes.  This latitudinal difference is energy gain and loss drives both ocean and atmospheric circulation.  All energy exchange by the oceans occurs at the surface  This exchange of energy controls the temperature of ocean water masses
  • 7. Density  Mass / volume (g / cm3)  Density depends on temperature and salinity  Ocean density ranges from 1.02 to 1.03 g/cc.  Density differences, together with winds, are the principal factors determining ocean currents.
  • 8. Freezing Water  Density curve (6.6) shows the relationship between the temperature or salinity of a substance and its density.
  • 10.  Water density decreases as the water freezes  Angle between water molecules expand from 105 ° to 109 °  Forms a crystalline lattice – less dense, hence ice float.
  • 11.  Sensible heat loss – detectable decrease in heat, measured with a thermometer, before ice freezes  Latent [hidden] heat of fusion – amount of heat removed to form ice per g of water (80 calories)  This process of freezing and thawing moderates global temperature swings. Why?
  • 12. Review the Concepts  Heat is transmitted in the ocean in which wave length?  Define density  The density of a parcel of seawater will be affected by which factors
  • 13. Evaporating Water  Latent heat of evaporation – amount of energy required to break hydrogen bonds  585 cal / g at 20 °C  Why such a big difference between latent heat of evaporation and the latent heat of fusion?
  • 14. Sea Water vs. Pure Water  Solids dissolved  No solids, water lowers specific heat requires 1 cal to by 4% (heats faster) heat up vs. 0.96 cal  Ions also interfere sea water. with the freezing  No ions to interfere point, the saltier the with the freezing lower the freezing point point
  • 16. Solar Energy Inputs  the sun 'makes a direct hit' at equator, while the same sunlight is spread over a larger area at the poles.  This is just another way of showing that the equator is heated up more than the north or south poles of the Earth.  This uneven heating of our round globe causes the air at the equator to rise, cool, and then wring out its moisture as rain.
  • 18.  The equator, then, is a zone of low pressure systems and lots of rainfall.  This zone extends from roughly 5°N to 5°S of the equator.  The air doesn't keep rising forever.  It eventually reaches an altitude where it is the same temperature (and density) as the surrounding air.
  • 19.  Itthen spreads out laterally, both in a north direction, and in a south direction.  As it moves poleward (either north or south from the equator), the air continues to cool, and finally, sinks. Where it sinks, the pressure is high.  Heat budget is balance (p.163, f. 7.10)
  • 21. Density Structure of the Ocean  Winds are the primary driving force of the surface circulation, which is also called wind- driven circulation,  density differences drive the deep, or vertical, circulation of the oceans.  The density of seawater is controlled by temperature and salinity, so the deep circulation is also called the thermohaline circulation.
  • 22. Review the Concepts  Contrastsea water and fresh water  What causes the seasonal changes?  Why the poles are cold?
  • 23.  Temperature differences as small as a few hundredths of a degree and salinity differences of a few parts  in a hundred thousand can be important.  Both temperature and salinity are conservative properties of seawater, that is, there are determined by processes occurring at the surface.
  • 24. Salinity  Salinity refers to the weight fraction of dissolved solids in water.  Average salinity of seawater is about 35‰ (‰ and ppt mean “parts per thousand).  Principal processes that change salinity are:  1. dilution (by rainwater and river water)
  • 25.  2. Evaporation freezing (& thawing) of sea ice  Salinity changes occur only at the surface of the ocean
  • 26.  Because temperature and salinity change only at the surface density changes occur only at surface  Water masses can be identified by their temperature-salinity characteristics.  Density, together with winds, govern ocean currents
  • 27. Ocean Structure  Upper 100-500 m to have uniform temperature and salinity because of mixing by waves.(6.13)  Below this, to a depth of ~1000 m, Temp., Salinity, and density change ( Thermocline, Halocline, Pycnocline) (6.12)
  • 29.  Indeep water, temperature, salinity and density are relatively uniform  This structure varies latitudinally. At mid-latitudes, it also varies seasonally: upper mixed layer will deepen in summer;  thermocline might largely disappear in winter
  • 31. Sound  Is a form of energy transmitted by rapid pressure changes in an elastic medium.  Intensity decreases as it travels through seawater until eventually is absorbed and converted into heat  Speed is 1,500 m / s, almost five time the speed in air
  • 32. Echolocation  Marine mammals use sound rather than light to “see” in the ocean  Echolocation –use of reflected sound to detect environmental objects  MM use echolocation to detect prey and avoid obstacles
  • 33.  Speed of sound increases as temperature and pressure increases (6.21)  Travels faster at the surface than in deeper, cooler water.  Minimum speed at 600 – 1,200 m  Below this depth the pressure offsets the temperature and speed increases again
  • 35. SOFAR Layer  Sound Fixing and Ranging  Transmission of sound in this minimum- velocity layer is very efficient because refraction tends to cause sound energy to remain within the layer (6.20)  Loud sounds made at this depth can be heard for thousands of kilometers  Sound generated in the India Ocean was hear as far a way as the Oregon Coast (Box 6.1)
  • 37. SONAR  Sound Navigation and Ranging  Active SONAR – projection of short pulses of high frequency sound to search for objects in the ocean.  Operator can tell direction, size, heading and even the composition by analyzing the composition of the returned ping
  • 39.  Side-Scan Sonar – towed behind a vessel (6.22)  Used for geological and archeological studies, and the location of downed ships and airplanes
  • 40. Review the Concepts  What kind of temperature does most of the world ocean has?  What is characteristic about the ocean's deep sound channel (sofar layer) ?  What is called a zone in which the ocean's salinity increases rapidly with increasing depth?  Which zone does the most pronounced or marked all year around thermoclines exist?