According to Wikipedia they explain the RE by saying: «If CO2 in the atmosphere is increased by one part per million, the CO2 in the ocean is increased by only a tenth of a part per million,
because of the way that the carbon dioxide in the water is partitioned between carbonate
ions and
bicarbonate ions and free CO2.
TA actually does increase slightly, but this is
because some solid calcium carbonate dissolves under the more acid conditions to yield carbonate
ions that then enter into the carbonate /
bicarbonate balance.