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 longterm climatic 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 has focused 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, soil science, 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 around the 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 program of 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.
, which was conducted on October 24–26, 2013, in the days preceding the annual meeting of the Geological Society of America, in Denver Colorado. The "critical zone" (or just the "CZ") has been defined as the near-surface environment where water, rock, air, and life meet in a dynamic interplay that generates soils, sustains ecosystems, and shapes landscapes. Understanding the chemical, physical, and biological processes that influence the CZ and the life it supports is important across a diverse range of problems, from assessing soil sustainability over timescales of human observation, to quantifying feedbacks between climate, weathering, and tectonics over millions of years. Increasingly, these problems are being tackled in exciting studies that are bridging a broad range of disciplines, from geophysics to geochemistry and from hydrology to soil science. This research is vital to understanding Earth's surface, which all humans rely on as a place to live and as a source of vital ecosystem services. Understanding processes that shape the CZ, including processes at depth, is vital to predicting how the CZ will respond to climate change and land-use intensification. By definition, the CZ extends from the outer periphery of the vegetation canopy to the lowest limits of freely circulating groundwater. Yet, thus far, subsurface CZ research has dominantly focused on just the upper 1-2 m or so of weathered rock and soil in landscapes. One of the great hurdles in understanding and quantifying processes in the deep CZ is depth itself; weathered rock and subsurface biota, the objects of study, are difficult to characterize in situ because they are mostly buried at difficult-to-access depths. The goal of this workshop was to develop a community-wide, cross-disciplinary consensus on how to overcome the traditional difficulties of deep CZ research. To this end, the workshop hosted 49 participants from 35 institutions scattered over 2 continents. Participants represented diverse disciplines, including geophysics, geochemistry, geomorphology, soil science, hydrology, and drilling technologies. Participants were also diverse in career level, ranging from second-year graduate students to directors of national and international facilities and programs. Over the course of two days of presentations, breakout groups, and plenary discussions, the following 10 outcomes, recommendations, and conclusions were reached: (1) There is strong interest and sense of excitement around advancing deep critical zone (CZ) research through a program of drilling, sampling, and geophysical imaging; (2) The CZ research community has now embarked on a long-term effort to unveil the deep critical zone at a scale appropriate to enhanced understanding of processes vital to the evolution of the CZ and to the prediction of CZ response to change in the future; (3) Shallow drilling and geophysical imaging projects do not have a funding source of their own, yet there is a need expressed across the community, including multiple disciplines, to support both drilling and geophysical studies of the deep CZ; (4) Overcoming limitations imposed by disciplinary silos will require new connections between CZ scientists, near-surface geophysicists, and experts in drilling technologies (some promising connections were made at the workshop); (5) Funding mechanisms must accept that proposals to study the CZ could (and often should) have strong geophysics and drilling components; funding of such work could alternatively be structured around a service model (similar to NCALM for LiDAR imaging) over the long-term; (6) Drilling and geophysics need to go hand in hand to capitalize on potentially powerful synergies and to understand the great compositional and spatial variability of the CZO; (7) The observations that are made using drilling and geophysical imaging should be driven from a hypothesis-testing framework; (8) The CZOs have already made many of the measurements needed to simultaneously test and demonstrate the value of geophysics and drilling with abundant existing data to fuel hypotheses; (9) A program of cross-disciplinary education is recommended to grow a new breed of CZ scientists who are educated in deep CZ investigation methods including drilling and geophysics; a good way to start may be to follow the REU model already established at NSF; (10) A panel of experts should be formed to serve in an advisory role for the growing community of scientists interested in deep CZ research using drilling and geophysical imaging.
