Enceladus, an ocean‐harboring moon of Saturn, erupts a plume that contains gases and frozen sea spray into space. By understanding the composition of the plume, we can learn about what the ocean is like, how it got to be this way, and whether it provides environments where life as we know it could survive. This study presents a new perspective for analyzing the plume composition to estimate the concentration of dissolved carbon dioxide in the ocean. We find that the derived range based on two different data sets is intriguingly similar to what would be expected from the dissolution and formation of certain mixtures of silicon‐ and carbon‐bearing minerals at the seafloor. The deduced combination of minerals may be indicative of a fundamental process that has sequestered a large amount of Enceladus' initial inventory of carbon dioxide into the rocky core. This inference echoes an emerging vision of a complex interior that hosts geochemically diverse environments. The dynamic interface of such complexity is where energy sources for possible life may arise.