In the case of normal seawater at pH 8.2, b = 0.19 meq/L/pH unit for the
boric acid/borate
system, and 0.63 meq/L/pH unit for the bicarbonate/carbonate system.
These values are
additive, and result in a total buffering of b = 0.82 meq/L/pH unit.
Under these
conditions, the boric acid/borate system provides about 23% of the total
buffering, while
the bicarbonate/carbonate system provides about 77%.
If the pH of normal seawater is raised to 8.5, the total buffering is b =
1.2 meq/L/pH
unit, or about 40% greater than at pH 8.2 (because both systems are closer
to the pKa).
At this pH, the relative contribution of the two systems to the total
capacity is only
slightly different than at pH 8.2, with 20% from borate and 80% from
carbonate.
If the pH of normal seawater is lowered to 7.8, the total buffering is b =
0.42 meq/L/pH
unit, or about half that at pH 8.2