How underwater mediation has transformed deep-sea spaces into resource-rich frontiers Green energy technologies such as windmills, solar panels, and electric vehicles may soon depend on material found at the seabed. How did a space once imagined to be empty and unfathomable come to be thought of as a treasure trove of resources? Lisa Yin Han traces how contemporary developments in underwater sensing and imaging materially and imaginatively transmogrify the ocean bottom into a resource frontier capable of sustaining a digitally connected global future. Set against the backdrop of climate change, energy transition, and the expansion of industrial offshore extractions, Deepwater Alchemy looks at oceanic media and its representation of the seabed in terms of valuable resources. From high-tech simulations to laboratories and archives that collect and analyze sediments, Han explores the media technologies that survey, visualize, and condition the possibility for industrial resource extraction, introducing the concept of extractive mediation to describe the conflations between resource prospecting and undersea knowledge production. Moving away from anthropocentric frameworks, she argues that we must equalize access to deep ocean mediation and include the submerged perspectives of multispecies communities. From the proliferation of petroleum seismology to environmental-impact research on seabed mining to the development of internet-enabled seafloor observatories, Deepwater Alchemy shows us that deepwater mediation is entangled in existential hopes and fears for our planetary future. As the ocean bottom becomes increasingly accessible to people, Han prompts us to ask not whether we can tame the seafloor, but, rather, why and for whom are we taming it?.