FUTURE TRENDS IN OCEANIC CRUSTAL HYDROGEOLOGY: LONG-SCALE TRANSPORT, CONTINUOUS MONITORING, AND MULTIDISCIPLINARY COLLABORATION

The basaltic oceanic crust comprises the largest aquifer on Earth, holding a volume of fluid equivalent to that stored in glaciers and ice caps, and larger than that stored in continental aquifers. The global flux of fluid driven hydrothermally through the oceanic crust is about as large as the fresh-water river flux to the ocean. These fluxes influence processes including the thermal evolution of oceanic plates; alteration of the lithosphere and the chemistry of flowing fluids; establishment and maintenance of subseafloor microbial ecosystems; and diagenetic, seismic, and magmatic activity along plate-boundary faults. Although the importance of oceanic crustal hydrogeology has been recognized for nearly 40 years, relatively little is known about the pathways through which fluids transport heat and solutes; the magnitudes of driving forces; or relations between geological, hydrological, geochemical, and microbiological processes and properties. We are entering a new phase of marine hydrogeologic experimentation and discovery, in which several kinds of studies are profoundly influencing our understanding of these systems. Studies of long-scale transport show that hydrothermal fluids may travel tens of kilometers within the oceanic crust. Continuous monitoring, both on and within the seafloor, reveals how these systems respond to natural and induced perturbations. Researchers in fields that operated independently in the past are designing and running complex, multidisciplinary experiments within the seafloor.