chemical oceanography

• COMPOSITION OF OCEANS

  • Dissolved Solutes
  • Nutrients
  • Gases
  • Trace Elements
  • Organic Compounds 
• Dissolved solutes come from freshwater runoffs that carry materials from terrestrial runoffs (EX. weathered rocks, minerals)
• Fresh water sources are rich in solutes
• 6 major ions in saltwater:

  • Chloride (most common), sodium (next most common), sulfate, magnesium, calcium, potassium, and bicarbonate
• • Bicarbonate comes from the reaction of CO2 dissolving in seawater (H2O + CO2 = H2CO3 and H+)
• Bicarbonate is important because it serves as a buffer, and counters the acidity of the ocean
• Cold, deep water is more acidic because cold water has higher saturation; more CO2 = more carbonic acid = harder to form calcium carbonate exoskeleton
• pH change affects marine organisms' ability to build shells or skeletons made out of CaCO3
• • Average pH of ocean: 8 (alkaline)
• • pH is the measure of the amount of hydrogen ions in the solution
• pH is in a logarithmic scale which means lowering an integer means more hydrogen ions → more acidic
• • pH differs from place to place
• Average salinity of ocean is 35 ppt 
• PPT means "parts per trillion" = 1 g of salt in 1 kg of water
• • Red Sea has 40+ ppt (more salt)
• • Particular ions are used to measure salinity (most commonly used is chlorine)
• Salinity varies by location:

  • Equator has low salinity (precipitation rates exceed evaporation rates)
  • Salinity is lowest in polar areas due to summer melt of ice leading to dilution and low salinity, which can go as low as 13 ppt
  • During non-summer months, water is saltier as saltwater freezes without the salt, increasing salinity
• Salinity in polar oceans is less stable because it is low in summer months and high in non-summer months
• Salinity varies per location:

  • Equator has low salinity because precipitation rates exceed evaporation rates
  • Poles have lowest salinity (unstable), especially during summer months. Salinity lowers during non-summer months.
  • Cold areas have the highest salinity because their waters are rich in solutes, making them have a lower freezing point
• The principle of constant proportion means the proportion of salts in different locations stays the same, even if their ppts (salinity) are different from each other
• Advantage of principle of constant proportions: stability/ consistency
• Proportions of the salt will have implications in the osmotic gradient
• Types of organisms based on salinity

  • Euryhaline – tolerant to salinity changes
  • Stenohaline – non-tolerant to saline changes
• • Salinometer or refractometer – measures electrical conductivity in solution
• Oceanic salinity is stable despite freshwater runoffs (major source of salt; from minerals, weathered rocks)
• Solutes in oceans amount annually to 2.5 × 1012 kg
• oceanic salinity is at a Steady-state equilibrium (there is enough output to offset the input)
• Ways the ocean loses salt:

  • Sea spray
  • Catching marine organisms
  • Evaporites
  • Adsorption
  • Redistribution of silica
• Sea spray - The saltwater mist that is blown off the sea by the wind.
• Catching marine organisms – human activity; they carry salts with them
• Evaporites – isolated salt deposits; they have more solutes than what water can hold and will become minerals that settle in the seafloor but don’t dissolve in the water (EX. Halide)
• Adsorption – when ions attach to surfaces, and they’re removed from the water (EX. Ferromanganese, potassium, magnesium)
• Redistribution of Silica – diatoms are made up of silicon dioxide which is released into the water as it dies or sinks down
• Nutrient elements are basal elements (organisms can't use them directly), while trace elements can be used directly but can be poisonous at large amounts
• The most abundant nutrient elements are: phosphorus, nitrogen, and silicon
• The most abundant trace element is lithium, while the least abundant is gold
• If there’s a spike in lead and mercury (trace elements), it can be dangerous to animals
• • Most abundant gases – oxygen, CO2, nitrogen
• There is more gas in cold water (due to high saturation)
• Saltier water normally lies below less salty water because it’s denser, BUT sometimes saltier water can lie ON TOP of less salty water when it's much warmer