Oceanography Chp 4

• Water molecule


  • Forms when electrons are shared between two hydrogen atoms and one oxygen atom
  • Covalently bonded
  • Angular shape
  • Polar (acts like a magnet)

  
• Cohesion


  Water molecules stick to each other
• Adhesion


  Water molecules stick to other materials (makes other materials wet)
• Capillary action


  Due to electrostatic forces (hydrogen bonds)
• Heat


  Energy from random vibrations of atoms or molecules
• Temperature


  • An object's response to an input or removal of heat
  • Measured in degrees
  • 1°C = 1.8°F

  
• Heat capacity


  • Measure of heat required to raise the temperature of 1 gram (0.035 ounces) of a substance by 1°C (1.8°F)
  • A calorie is the amount of heat required to raise the temperature of 1 gram of pure water by 1°C (1.8°F)

  
• Water temperature and density

  • Density = mass per unit volume
  • Most substances become denser as they get colder
  • Transition from water to ice-density of water decreases abruptly

  
• Freezing water


  • Bond angles expand as water freezes (105° in liquid to 109° as ice)
  • Molecules are packed less efficiently
  • Mass decreases from 0.999g as liquid to 0.917g as ice
  • 9% expansion
• Sensible heat


  Detectable and causes a temperature change
• Latent heat


  Hidden and is heat input that does not cause a temperature change but produces a change of state

  
• Evaporating water


  • Requires heat to break hydrogen bonds
  • These bonds are strong and energy required to break them is known as the latent heat of vaporization

  
• Thermal inertia


  Tendency of a substance to resist temperature change with the gain or loss of heat energy
• Thermal equilibrium


  Incoming heat equals outgoing heat

  
• Density structure of ocean

  • Seawater's density increases with increasing salinity, increasing pressure and decreasing temperature
  • 3 main density zones: Surface zone, Pycnocline, Deep zone

  
• Surface zone


  • Mixed layer
  • Temperature and salinity are relatively constant with depth
  • Water is in contact with atmosphere
  • Exposed to sunlight
  • 2% of ocean volume
  • Least dense
• Pycnocline


  • Below pycnocline
  • 80% of ocean water
  • Little change in density with depth

  
• Deep zone


  • Zone where density increases with increasing depth
  • Approximately 18% of all ocean waters
  • Isolates surface water from denser water below
• Thermocline


  • Middle layer
  • Zone which temperature changes rapidly with depth
  • Mid and low latitude phenomenon
  • Depth depends on season, availability of sunlight, latitude, weather, currents

  
• Halocline


  • Zone of rapid salinity increase with depth
  • Often combines with thermocline
• Refraction

  When a wave of light or sound leaves a medium of one density and enters another, changing speed and therefore bending
• Light in ocean

  • Below sea surface light is weakened by scattering and absorption
  • Scattering is when light bounces off other molecules
  • Absorption is when light is absorbed by other molecules and light energy is converted to heat
• Natural light


  • Blue predominates
• Strobe light


  • Other colors appear as distance to camera is small and not all of the colours absorbed
• Sound in the ocean

  • Decreases as it travels through seawater
  • Spreading, scattering & absorption
  • Absorption of sound is proportional to the square of the frequency of the sound
  • Sound waves travel more efficiently through water than light waves before being absorbed
• Sound vs depth


  • Speed of sound increases with increased temperature and pressure
  • Travels faster in warmer water
  • At bottom of ocean pressure overrides temperature and sounds speeds up
• Sofar layer


  • Sound fixing and ranging
  • Minimum velocity layer
  • Approximately 1000 m in depth (over 3000 ft)
  • Sound waves bend toward layers of lower sound velocity and stay within this zone
• Sonar


  • Sound Navigation and Radar
  • Projection and return of high frequency pulses ("pings")
  • Bounces off object larger than wavelength of sound
  • High frequency converted to within range of human hearing
• Side scan sonar


  • Active sonar
  • Up to 60 transmitters/receivers
  • More accurate
  • Used for geological investigations, archaeological studies and location of wrecks
  • Similar to multibeam system
• Dissolving power of water

  • Water is a powerful solvent
  • Due to polar nature
• Salinity


  • The total quantity (or concentration) of dissolved inorganic solids in water
  • 3.5% of seawater is dissolved substances (average)
• Source of ocean's salts


  • Weathering and erosion of rocks
  • Excess volatiles from outgassing
  • Mid ocean ridges and rifts
  • Hydrothermal vents
• Principle of constant proportions
• Determining salinity


  • Measure chlorinity
  • Chlorinity is measured of the total weight of chlorine, bromine and iodine ions in seawater
  • Proportion of chlorinity to salinity is constant
  • Salinity in (0/00) =1.80655 X Chlorinity (0/00)
• Salinometer


  • Measures electrical conductivity of seawater
  • Converts conductivity to salinity
  • Conductivity varies with concentration, mobility of ions, temperature

  
• Chemical equilibrium


  • Proportion and amounts of dissolved salts per unit volume of ocean are nearly constant
  • "Steady State ocean"
• Residence time


  • Residence time= Amount of element in ocean/Rate at which element is added or removed from ocean
  • Residence time is approximately 4100 years for ocean water
  • Mixing time for ocean is about 1600 years
• Dissolved gases


  • Major gases in seawater are nitrogen (48%), oxygen (36%) and carbon dioxide (15%)
  • Gases dissolve most readily in cold water
• Acids


  Any compound that releases hydrogen ions in a solution
• Bases


  Any compound that accepts hydrogen ions in solution