October 24-26, 2013
Drilling, Sampling, and Imaging the Depths of the Critical Zone
Conveners: Clifford Riebe and Jon Chorover
October 24-26, 2013
Hilton Garden Inn
1400 Welton Street
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conveners with any
How to Register:
Please use the navigation at the right to register for the workshop. Be sure to take a look at the schedule as well; we
have a great group of speakers and lots of time for discussion. Please feel free to contact the conveners with any
questions! Should you have difficulty with the registration form, please email the webmaster directly,
How to Contribute to the Workshop (White Papers):
The main goals of this workshop are to foster discussion about drilling, sampling and imaging of the critical zone, and to
coordinate possible follow-up actions to advance understanding of deep CZ science. We ask that all participants come
prepared to contribute to the discussion. To this end, we strongly encourage participants to prepare and submit a short,
1-2 page white paper that highlights a key science objective or a specific drilling target or a conceptual approach that
addresses the workshop objectives. These white papers should be as specific as possible, and they may, e.g., identify
a team of proponents, for whom the lead proponent attends the workshop. White papers can be uploaded during the
application process (see navigation to the right) or they can be submitted to one of the workshop organizers later. During
and immediately following the workshop, white papers will be amalgamated into a master document. Thus, an additional
benefit to participants will be to stimulate collaboration toward complementary proposed research goals. To help get you
thinking about your white paper, we provide some motivation for the workshop below.
Motivation for a Workshop on the Deep CZ:
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 how weathering
and climate influence each other over millions of years. Increasingly, these problems are being tackled in exciting,
cross-disciplinary studies of the "critical zone" (CZ) (Brantley et al., 2006; 2007; Chorover et al., 2011) - 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 (NRC, 2001).
The Soil is Not Enough:
By definition, the CZ extends from the uppermost periphery of vegetation to the lowest limits of freely circulating
groundwater. Yet, thus far, subsurface CZ research has focused mostly on just the upper 1-2 m or so of weathered rock
and soil in landscapes (Dietrich, 2010). Although this work has shed much informative light on how soil is produced
(e.g., Heimsath et al., 1997) and removed (e.g., Riebe et al., 2004; Dixon et al., 2009) from landscapes, it is now
increasingly recognized that the top 1-2 m is often profoundly influenced by processes that occur beneath it, in saprolite
and fractured rock that can collectively extend to depths approaching 100 m or more in some landscapes (Detheir and
Lazarus, 2006; Chorover et al., 2007; Graham et al., 2010; Anderson et al., 2011; Befus et al., 2011; Bales et al., 2011;
Brantley and Lebedeva, 2011).
This deeper layer, referred to here as the "deep CZ", lies below the limits of most CZ studies to date and thus has been
aptly referred to as the "unmeasured zone" (Dietrich, 2010). Yet, based on the few studies that have reached into the
deep CZ, it is clear that much more work is needed to identify and understand the complex surface-subsurface
interactions and feedbacks that are inherent in the development and maintenance of weathering profiles and the
ecosystems they support. For example, there are clear indications that the chemistry and hydrologic response of
streams at the surface may often depend crucially on CZ processes in complex fractured bedrock systems at depth
(e.g., Anderson et al., 2002; Onda et al., 2004; Langston et al., 2011; Kuntz et al., 2011). This implies that
characterization of the deep subsurface is crucial to predicting how the CZ will evolve in a changing climate. In addition,
it has been shown that the degree of weathering in saprolite may be a key regulator of soil production (e.g., Burke et al.,
2007; Dixon et al., 2009), making quantitative understanding of the deep CZ crucial to addressing topics ranging from
soil sustainability to landscape evolution. Surface processes affect and also depend on deep weathering (Frazier and
Graham, 2000; Clarke and Burbank, 2011), raising the prospect of exciting, yet-to-be explored feedbacks among
landscape evolution, regolith formation, biogeochemical cycling and hydrologic processes (Brantley et al., 2011). Hence
it is evident that deep CZ research is a key 21st Century frontier for a number of subdisciplines within the broad field of
Earth-systems science, including watershed hydrology, geobiology, geomorphology, soil science, and low-temperature
geochemistry (e.g., NRC, 2010).
Overcoming the Challenges of Deep CZ Research:
One of the great hurdles in understanding and quantifying processes in the deep CZ is depth itself; regolith and
subsurface biota, the objects of study, are difficult to characterize in situ because they are mostly buried at
difficult-to-access depths (Montgomery and Dietrich 2002; Heilweil et al., 2006; Winter et al., 2008; Sherriff et al., 2009;
Befus et al., 2011). Near-surface geophysical techniques can be employed to help image the subsurface over broad
scales (Robinson et al., 2008; Samouëlian et al., 2005), but interpretation of such images is problematic in the absence
of direct observations of physical and chemical properties of material at depth. Such direct observations can be made by
drilling and coring, for spot sampling of solid-phase geochemistry, microbiology, pore-water solutions, and other material
properties (e.g., Begonha and Braga, 2002; Olona et al., 2011). Boreholes from drilling also provide access for pump
tests and installation of long-term hydrologic and geochemical monitoring equipment (Marechal et al., 2004; Day-Lewis
et al., 2006). Yet the logistics and technical difficulties of coring make minimally perturbed, representative samples
difficult to obtain, especially from deep boreholes that would be ideal for long-term monitoring installations.
Coring and borehole installations are time-consuming and expensive, placing practical limits on the number of holes that
can be drilled in the characterization of the deep CZ. Hence it is crucial to make each drilling effort as effective as
possible at addressing key questions about the deep CZ in different landscapes. To achieve this goal, studies of the
deep CZ need to be able to optimize locations of boreholes, to provide a high yield of data per unit cost invested in
drilling and instrumentation. The traditional approach to identifying prime borehole locations involves geophysical imaging
of the subsurface during preliminary site investigations (e.g., Kieft et al., 2007). In deep CZ research, geophysical
imaging of the subsurface takes on added importance in the aftermath of coring, as a way to extrapolate the spatial
extent of subsurface heterogeneities (e.g., Robinson et al., 2008; Befus et al., 2011) observed in individual cores. Such
heterogeneities are commonly both extensive and may be key targets of study for hydrologists, soil scientists,
geobiologists, biogeochemists and geomorphologists alike (e.g., Banfield et al., 1998; Hubbard and Rubin, 2000; Gao et
al., 2007; Massoud et al., 2010; Graham et al., 2011).
In a synergistic development for deep CZ research, the field of near-surface geophysics is in the midst of an ongoing
renaissance, with its own new focus group within the American Geophysical Union and a recently established journal,
titled Near Surface Geophysics (Yaramanci and Lange, 2003). This is tangible evidence of a growing community of
geophysicists who are interested in what we refer to here as the deep CZ. Moreover, it dovetails nicely with recent efforts
by diverse researchers from the Earth sciences community who are advancing towards research goals through
revitalized commitments to continental scientific drilling in the US (Brigham-Grette et al., 2011).
In summary, there is currently an alignment of (i) broad interest and community-perceived importance in making
advances in deep CZ research, (ii) the blossoming of near-surface geophysics as a vital new subdiscipline in the Earth
sciences, and (iii) advances and renewed efforts in continental scientific drilling. Circumstances are nearly ideal for
making substantial, synergistic advances in understanding Earth's critical zone from the bottom up. The researchers,
tools, and techniques are all in place. All that is needed is a community-wide consensus on how best to move forward
with exploration of the deep CZ.
Moving Forward -- A Workshop on Deep CZ Research:
To develop a community-wide, cross-disciplinary consensus on how to overcome the traditional difficulties of deep CZ
research, we are organizing an NSF workshop in October 2013. This workshop will bring CZ researchers together with
geophysicists, as well as Earth systems engineers and scientists with significant expertise on drilling, coring and
borehole instrument installations. Our intent is to use the workshop as a springboard for further activities, including
development of a community-based proposal for funding that advances critical zone research through drilling, coring,
imaging and instrumenting of the deep CZ.
We have designed the workshop to highlight the challenges of subsurface characterization (e.g., Russel et al., 1992;
Robinson et al., 2008), and elaborate on ways to overcome them for improved understanding of the propagation of
weathering and associated hydrologic and biogeochemical processes at depth. The overarching goal of deep CZ coring
and imaging activities (the intended outgrowth of the workshop) is to assess how deep (i.e., 10's to 100's of meters)
subsurface processes produce regolith, shape landscapes and affect hydrologic response in different climatic, tectonic
and lithologic settings.
The workshop will bridge a suite of disciplinary gaps; we judge that the key to a successful workshop in this case lies in
fostering productive new collaborations among scientists and engineers from diverse disciplines. On one side are the
biogeochemists, geobiologists, hydrologists, geomorphologists and soil scientists who can help identify the most
pressing questions at the forefront of deep CZ research. On the other are the geophysicists and drilling engineers and
scientists who can help answer the questions through acquisition and interpretation of high quality samples and images
of the subsurface.
How the Workshop Will Be Conducted:
Our workshop will focus on the three themes of (i) drilling, (ii) sampling and (iii) imaging the deep CZ. Discussions
surrounding each theme will be initiated by oral presentations from speaker and two experts in each field. We will also
host a poster session, including student-authored presentations related to each theme. Themes 1 and 2 on drilling and
sampling (which we view as being especially complementary) will be the focus of the morning of day 1. Presentations in
the morning will help fuel discussions in breakout groups in the afternoon. After a plenary synthesis of Day 1 activities,
the workshop will break for dinner and reconvene on the morning of Day 2 for presentations and breakout groups on near
surface geophysics. The workshop will conclude in the afternoon on Day 2 after a synthesis of key concepts of the
workshop and elaborates on a way forward.
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