Throughout its life the ocean crust is a key boundary between Earth’s interior and the oceans/atmosphere. Hydrothermal circulation of seawater-derived fluids through the cooling and aging crust results in chemical exchange between Earth’s interior and oceans and atmosphere, playing an important role in long-term biogeochemical cycles. Altered ocean crust provides a time-integrated record of its geochemical exchange with seawater. Furthermore, hydrothermal minerals formed from ridge flank fluids record the evolving chemistry of the overlying oceans – itself an integrator of a range of Earth processes. I will present an overview of how scientific ocean drilling experiments across ridge flanks contribute to our understanding of the processes that control ridge flank hydrothermal exchanges, the role these exchanges play in global geochemical cycles, and the extent to which they record and respond to wider changes in the Earth system. In particular, the South Atlantic Transect (IODP Expeditions 390/393), designed to recover the upper crust and overlying sediments across the western flank of the slow-spreading Mid-Atlantic Ridge to investigate hydrothermal aging and microbiological evolution of the ocean crust, and the paleoceanographic evolution of the overlying South Atlantic.