In the ocean, alkalinity is completely dominated by carbonate and bicarbonate plus a small contribution from borate. 
Thus the chemical equation for alkalinity in seawater is: 
: A = [HCO] + 2[CO] + [B(OH)]
There are many methods of alkalinity generation in the ocean. Perhaps the most well known is the dissolution of calcium carbonate to form Ca and  (carbonate). The carbonate ion has the potential to absorb two hydrogen ions. Therefore, it causes a net increase in ocean alkalinity. Calcium carbonate dissolution occurs in regions of the ocean which are undersaturated with respect to calcium carbonate.
The increasing carbon dioxide level in the atmosphere, due to carbon dioxide emissions, results in increasing absorption of CO from the atmosphere into the oceans. This does not affect the ocean's alkalinity but it does result in a reduction in pH value (called ocean acidification). Ocean alkalinity enhancement has been proposed as one option to add alkalinity to the ocean and therefore buffer against pH changes. 
Biological processes have a much greater impact on oceanic alkalinity on short (minutes to centuries) timescales. Aerobic respiration of organic matter can decrease alkalinity by releasing protons. Denitrification and sulfate reduction occur in oxygen-limited environments. Both of these processes consume hydrogen ions (thus increasing alkalinity) and release gases (N or HS), which eventually escape into the atmosphere. Nitrification and sulfide oxidation both decrease alkalinity by releasing protons as a byproduct of oxidation reactions.