Midterm #2

• Salinity displays a latitudinal dependence.
• Salinity is highest between 20-30 ° north and south.
• Salinity decreases near the equator and the poles.
• Freshwater is added to the ocean through:

  • Precipitation
  • River runoff
  • Ice melting
• The addition of freshwater to the ocean, decreases the ocean's density.
• Freshwater is removed from the ocean through:

  • Evaporation
  • Ice formation
• The removal of freshwater from the ocean increases the ocean's density.
• The formation of ice increases ocean density as ice does not contain salt, therefore it increases the salinity of the surrounding water.
• Surface salinity is largely regulated by climate (evaporation/precipitation).
• A change in density due to salinity can be measured by: Evaporation (removal) - Precipitation (addition)
• Fill in the following table with minimal, moderate, or maximal.

  A) Minimal

  B) Moderate

  C) Maximal

  D) Maximal

  E) Minimal

  F) Maximal

  G) Minimal

  H) Maximal

  
• Halocline: a zone in the water column where salinity changes rapidly with depth.
• Water stratification due to salinity occurs between 40 °N and 40 °S where high salinity surface water sits on top of less saline, colder water.
• Below 2 km in depth, salinity remains relatively constant.
• Density: amount of mass per unit of volume (e.g., g/cm^3).
• Density varies with:

  • Temperature (inverse)
  • Salinity (direct)
  • Pressure (so small, is negligible)
• Cold, saline water is more dense than warm freshwater.
• Warm water with high salinity can overlie cold water with low salinity.
• Pycnocline: a zone in the water column where density changes rapidly with depth.
• Layers of the water column:

  • Surface layer (2 %)
  • Pycnocline layer (18 %)
  • Deep layer (80 %)
• The surface layer of the ocean is on average 100 m thick.
• The surface layer of the ocean fluctuates diurnally, seasonally, and annually.
• Diurnal: daily.
• The surface layer of the ocean is lighted, which allows for photosynthesis to occur.
• The pycnocline layer of the ocean has a permanent pycnocline in tropic regions.
• The pycnocline layer of the ocean coincides with the halocline in midlatitude regions.
• The deep layer of the ocean originates in the high latitudes and is very cold (~4°C).
• The pycnocline layer of the ocean isolates the deep layer from the surface layer.
• Saturation value: the amount of gas at equilibrium that can be dissolved by a volume of water.
• As salinity increases, solubility decreases.
• As temperature increases, solubility decreases.
• As pressure increases, solubility increases.
• High salinity decreases solubility as the water is more saturated with salt ions.
• High temperature decreases solubility as faster moving particles will release gas easier than slower moving particles.
• High pressure increases solubility as the collision frequency increases.
• Brackish: mix of salt and freshwater.
• At the same pressure, cold brackish water can dissolve more gas than warm saline water.
• Supersaturation: a solution with a concentration of solute that exceeds the amount dissolved at saturation.
• Undersaturation: a solution with a concentration of solute that is less than the amount dissolved at saturation.
• The primary regulator of gas concentrations in water is the activity of organisms.