What is alkalinity?
The buffering capacity of the ocean (resists a pH change)
What does alkalinity refer to?
The amount of bases in a solution
What do bases do?
They accept protons such as H+
How do bases assist alkalinity in a solution?
if there are more bases in a solution (i.e. more alkalinity), then more hydrogen ions are absorbed which prevents them from reducing pH
Is bicarbonate (HCO3-) an acid or a base?
It is both an acid and a base
WHY? it can accept a proton (H+) to become carbonic acid or give up a proton (H+) to become carbonate
Is carbonate (CO32-) an acid or a base?
It is a base because it has twice the buffering capacity as bicarbonate given its 2- charge
It can accept protons (H+) to become H2CO3
What form is most of the inorganic carbon in the ocean taking?
Bicarbonate (HCO3-) → about 90%
Which substances constitute the major buffering capacity of the ocean?
Bicarbonate and carbonate
What percentages of bicarbonate and carbonate contribute to alkalinity?
Bicarbonate: 89.8%
Carbonate: 6.7%
What does “carbonate alkalinity” refer to?
Bicarbonate and carbonate
What is total alkalinity?
All of these ions can accept an H+ and buffer against acidification
How does rain form?
Small and large droplets collide and coalesce → droplets become bigger → droplets split into rain
When a rain droplet forms, what does the CO2 in the air around it do?
There must be equilibrium between the water and the air, so CO2 must equilibrate with the solution of the droplets to ensure Henry’s Law is followed
Atmospheric CO2 dissolves into the water droplet
What will the expected pH of the water droplet be?
The pH is likely to be low because there is no buffering capacity, so it will be acidic
Explain alkalinity in non-ocean waters
Chemical weathering of rocks runs off into rivers
Limestone that gets exposed to low pH rainwaters dissolves → sinkholes, which when flooded with SLR become “blue holes”
CaCO3 dissolves because the carbonate is being lost to form bicarbonate; water becomes corrosive
What chemical status in water controls weathering and the release of alkalinity?
pH
When water’s carbonate concentrations are low, carbonate-bearing rocks (CO3-) will begin to dissolve/weather → carbonate concentration declines, meaning lower pH/higher acidity
What characteristics make ions capable of buffering?
ability to capture H+ ions
What is the most important source of alkalinity in the ocean?
chemical weathering of rocks; river run-off
