Chemistry

• Major constituents of seawater?

  Salt - NaCl
• Minor constituents in seawater?

  Lithium and iodine
• Trace components in seawater?

  Copper and radionuclides
• What happens to river salts?

  Some are conservative: Not changed by biological or chemical processes

  Some are non-conservative: React with chemical or biological processes
• Residence time (yr) = Total amount of substance in reservoir (tonnes)/ Sum of fluxes into or out of reservoir (tonnes per year)
• Volume of the ocean $1,335,040 *$$103 km^3$
• Seawater with salinity of 35 g/L has chloride conc of 19.35 g/L
• The solubility of a gas will increase with its partial pressure
• Henry's law - for some gases the concentration in a solvent at a known temperature is proportional to partial pressure of the dissolving gas

  c = KH * p
• A liquid is saturated with a gas when it is at equilibrium with the gas above it.

  Factors:

  • Partial pressure of gas
  • Temperature
  • Composition of the liquid
• Black Sea

  • Input of water to system via rivers and rainfall
  • Output via Bosphorus Strait, depth of 13 to 110 metres
  • Central Black Sea - depth of 2000 metres
  • Significantly lower salinity than typical global ocean
• $pH =$$-log10 [H^+]$
• Surface seawater has a pH of 8.1
• CO2 cycle in seawater:

  • Atmospheric CO2 equilibrates with the seawater
  • It becomes hydrated
  • Carbonic acid dissociates
• If temperature increases CO2 in seawater decreases
• A buffered solution resists change in pH when it is diluted or when acid or base is added
• Oceans are well buffered against changes in pH
• Carbonate alkalinity = [HCO3-] + [CO32-]
• Calcium carbonate

  • Used by many planktonic organisms to form skeleton
  • Major element - concentration only slightly changes with depth
• Sunken shells form biogenic sediments
• Calcium carbonate forms:

  • Calcite - more stable, able to survive to greater depths
  • Aragonite - less stable, start to dissolve at shallower depths
• Surface waters are supersaturated in calcium carbonate

  Deep oceanic waters are generally unsaturated in these compound

  Shells start to dissolve in the water column or on the seabed
• Very little Nitrogen reaches or remains in deep ocean sediments