COMPOSITION OF SEA WATER, WAVE FORMATION, AND SEA CURRENT

• Composition of Seawater


  • Water (96.5%)
  • Salts (2.5%)
  • Other small things (e.g. particles, gases)
• Salinity


  Measure of the salt content in seawater, typically between 34 to 37 parts per thousand (ppt)
• Main ions in seawater

  • Chloride (Cl⁻)
  • Sodium (Na⁺)
  • Sulfate (SO₄²⁻)
  • Magnesium (Mg²⁺)
  • Calcium (Ca²⁺)
  • Potassium (K⁺)
• Other major dissolved substances in seawater

  • Inorganic carbon
  • Bromide
  • Boron
  • Strontium
  • Fluoride
• Dissolved substances in seawater

  • Play important roles in various chemical processes and the overall chemistry of seawater (e.g. freezing, melting, photosynthesis, oxidation-reduction reactions, buffer mechanism, carbonate chemistry, geochemical cycles)
• Minor dissolved constituents

  Inorganic phosphorus and nitrogen, crucial for the growth of marine organisms as nutrients supporting the marine food web
• Dissolved gases in seawater

  • Nitrogen
  • Oxygen
  • Argon
  • Carbon dioxide
• Seawater

  • Higher salinity increases its viscosity (internal resistance to flow) and density, resulting in a lower freezing point and a higher boiling point than pure water
• Sources of chemicals in seawater

  • Rivers (carrying dissolved minerals and nutrients)
  • Wind (transporting dust, pollen, and other particles)
  • Hydrothermal solutions (releasing hot, mineral-rich fluids)
  • Biological processes (e.g. phytoplankton uptake and decomposition)
• Principal components of seawater

  • Dissolved inorganic substances (e.g. chloride, sodium, magnesium, sulfate, calcium, potassium)
  • Dissolved organic substances (e.g. carbohydrates, amino acids, lipids, humic substances)
• Salinity


  Oceans get as much salt as they lose, keeping the salt content stable; Salinity varies from 33 to 37 grams of salt per kilogram of seawater, mainly affected by evaporation and precipitation
• Factors affecting ocean temperature

  • Sunlight (warmer near the equator, cooler towards the poles)
  • Seasons (warmer in summer, cooler in winter)
  • Land (cold air from land can cool the ocean surface, warm air can warm it up)
  • Currents (warm water currents from the equator, cold water currents)
• Nutrients and biogeochemistry


  Inorganic phosphorus and nitrogen are critical nutrients for marine organisms; Silicate is essential for the growth of diatoms; Trace elements like iron, zinc, cobalt, and copper are essential cofactors for enzymatic reactions
• Waves


  Movement of water molecules in the ocean's surface layers, caused by the collision of air and water molecules and the transfer of energy from the wind

  
• Causes of waves

  • Wind (wind-driven waves)
  • Gravitational pull of the sun and moon (tides)
  • Underwater disturbances (tsunamis)

  
• Waves are energy passing through the water, causing it to move in a circular motion, not travelling bodies of water
• As a wave passes through water, a column of water below the surface completes the same orbital motion, which is disturbed by the seafloor in shallow areas, causing the wave to break

  
• Most common ocean waves are surface waves, caused by wind

  
• Waves do not transmit water across the sea, they only transmit energy
• As a wave passes through water, not only does the surface water follow an orbital motion, but a column of water below it (down to half of the wave's wavelength) completes the same movement

  
• The approach of the bottom in shallow areas causes the lower portion of the wave to slow down and compress, forcing the wave's crest higher in the air
• Eventually the imbalance in the wave reaches a breaking point, and the crest comes crashing down as wave energy is dissipated into the surf

  
• Types of ocean waves

  • Surface waves
  • Storm surge
  • Tsunami

  
• Surface waves


  Caused by wind blowing along the air-water interface, creating a disturbance that steadily builds as wind continues to blow and the wave crest rises

  
• Storm surge

  A series of long waves that are created far from shore in deeper water and intensify as they move closer to land

  
• Tsunami

  Very long waves created by submarine earthquakes or landslides that displace a large amount of water very quickly

  
• Storm surges and tsunamis do not create a typical crashing wave but rather a massive rise in sea level upon reaching shore, and they can be extremely destructive to coastal environments

  
• How waves are formed

  1. Winds push some parts of the water down which in turn pushes other parts of the water up, creating a cycle that forms a wave

  2. The more intense the wind blows, and the longer it blows for, the bigger and stronger the wave will become

  3. The further the distance the wind travels, the greater the fetch and the greater the wave size

  4. As the wave approaches the shore, the cycle created by the wind begins to break and the waves interact with the shape of the coastline and the underwater geography

  
• Swell

  • Waves created by winds travelling across the ocean that form into patterns of larger and smaller wave groups
  • Wavelength is the distance between two wave crests
  • Wave height is the vertical distance between the crest and the preceding trough
  • Swell period is the time between wave crests

  
• Three main factors affecting wave formation

  • Wind velocity
  • Fetch
  • Duration
• The greater the wind velocity, the longer the fetch, and the greater duration the wind blows, then the more energy is converted to waves and the bigger the waves
• Ocean current

  A stream made up of horizontal and vertical components of the circulation system of ocean waters that is produced by gravity, wind friction, and water density variation

  
• Ocean currents

  • Transfer significant amounts of heat from Earth's equatorial areas to the poles and thus play important roles in determining the climates of coastal regions
  • Influence and are influenced by atmospheric circulation

  
• General circulation of the oceans

  The average movement of seawater, which follows a specific pattern and includes oscillations of tides and waves, as well as meanders and eddies

  
• Horizontal movements

  Currents, which range in magnitude from a few centimeters per second to as much as 4 meters per second
• Vertical movements

  Upwelling and downwelling, which exhibit much lower speeds, amounting to only a few meters per month
• Causes of ocean currents

  • Pressure gradients
  • Coriolis effect
  • Geostrophic current

  
• Pressure gradients

  The change in water pressure over a certain distance in the ocean, which creates a force that drives the movement of water from an area of higher pressure to an area of lower pressure
• Coriolis effect

  The deflection of moving water caused by the rotation of the Earth, which causes currents to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
• Geostrophic current


  A type of oceanic flow where the pressure gradient force is balanced by the Coriolis effect, resulting in a current that flows along the contours of equal pressure