Chapter 7 Ocean Chemistry.ppt

Ocean Salinity Salinity is the total quantity of dissolved inorganic solids in water. 3.5% salt on average measured in g/kg (ppt = parts per thousand) Major Constituents = [] 1 part per million Na+ Sodium Cl- Chloride SO4- Sulfate Mg2+ Magnesium Ca2+ Calcium K+ Potassium Residence time: the average time a substance remains in solution in the ocean Total amount divided by rate of input (or output) The ratio of dissolved solids in the ocean is constant: Well-mixed solution Principle of Constant Proportions : the ratios between the concentrations of major conservative ions in open-ocean water are constant Salt composition constant for last 1.5 billion years 5*1022g= total dissolved material 2.5*1015g=total run off per year salinity is not increasing! therefore: rate of addition ~ rate of removal Seawater’s constituents may be conservative or nonconservative Conservative = concentration changes only as a result of mixing, diffusion, and advection Non-conservative = concentration changes as a result of biological or chemical processes as well as mixing, diffusion, and advection Distribution with depth Photosynthesis removes CO2 and produces O2 at the surface Respiration produces CO2 and removes O2 at all depths Compensation depth (Photosynthesis = Respiration) CO2 O2 Non-pure water solutions [OH-] and [H+] are inversely proportional Imbalance between the relative concentration of H+ and OH- produces an acidic or basic solution pH scale-measures acidity/alkalinity 0-14 Logarithmic scale: pH=-log10[10-5]=5 pH of rainwater ~ 5-6 (on the acidic side) Seawater Alkaline, pH from 7.5-8.5 Average pH=7.8 pH relatively constant due to buffering action of CO2 Buffer = substance that prevents sudden or large changes in the acidity or alkalinity of a solution Important for biological processes pH inversely proportional to the concentration of CO2 pH: acidity of seawater 7.5 - 8.5 Car