This chapter will discuss exchange processes that control Titan's global chemistry and thus its habitability: e.g., impact cratering, cryovolcanism, degassing. We review the available work constraining the extent of exchange between Titan's ocean and surface. Cassini-Huygens observations provide a better picture of the composition and structure of the ice but do not reveal the extent of its tectonics or overturning, if any. Improved laboratory data are enabling models of the interior structure and overturning, coupled with transport from impacts. Impacts may provide a mechanism for local downwelling of such materials. Such downwellings may be of interest for modeling chemical disequilibria at the ice-water interface, but on a global scale, they are unlikely to contribute significantly to the flux of chemicals driving energetic disequilibrium in Titan's ocean. Future missions will be needed to understand the nature of the exchange between Titan's ocean and surface.
Keywords: Habitability; Geochemistry; Impacts; Cryovolcanism; Degassing
