Deep meteoric waters comprise a key component of the hydrologic cycle,
transferring water, energy, and life between the earth's surface and
deeper crustal environments, yet little is known about the nature and
extent of meteoric water circulation. Using water stable isotopes, we
show that maximum circulation depths of meteoric waters across North
America vary considerably from 1 to 5 km, with the deepest circulation
in western North America in areas of greater topographic relief.
Shallower circulation occurs in sedimentary and shield-type environments
with subdued topography. The amount of topographic relief available to
drive regional groundwater flow and flush saline fluids is an important
control on the extent of meteoric water circulation, in addition to
permeability. The presence of an active flow system in the upper few
kilometers of the Earth's crust and stagnant brines trapped by negative
buoyancy offers a new framework for understanding deep groundwater
systems.