NSF workshop: Drilling, sampling, and imaging the depths of the critical zone

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Understanding the chemical, physical, and biological processes that modulate Earth's surface is important across a diverse range of problems, from assessing soil sustainability over human timescales, to understanding weathering-related feedbacks in Earth's longtermclimatic evolution. Increasingly, these problems are being tackled in exciting, crossdisciplinary studies of the "critical zone" (CZ). Although, the CZ is considered to extend to the lowest limits of freely circulating groundwater, most subsurface CZ research hasfocused on just the upper 1-2 m or so of weathered rock and soil in landscapes. Hence the deep CZ (i.e., anything that is too deep to readily access and sample by hand) represents a crucial frontier for advances in watershed hydrology, geobiology, geomorphology, soilscience, and low-temperature geochemistry. One of the hurdles in studying the deep CZ is depth itself; regolith, pore waters, and subsurface biota are difficult to characterize in situ because they are mostly buried at difficult-to-access depths. Tackling the challenge of deep CZ research will require coordinated investigations that exploit recent advances in drilling, sampling, monitoring and imaging of the subsurface.This award will support a workshop designed to develop a community-wide, crossdisciplinary consensus on how to overcome the traditional difficulties of deep CZ research. The workshop will bring together 45 people, including CZ researchers and near surface geophysicists, as well as engineers with experience in drilling, coring and borehole instrumentation. It exploits the chance alignment of: (i) an increasing need for advances in deep CZ research, voiced in a recent consensus of CZ scientists from aroundthe world; (ii) recent advances in near-surface geophysics, including improved techniques for imaging the deep CZ and interpreting geophysical properties in terms of CZ architecture; and (iii) recently renewed momentum behind establishing a formal programof continental scientific drilling in the US. To be effective, the workshop will need to bridge gaps, fostering productive new collaborations among scientists and engineers from diverse disciplines.