New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 74

other individual processes into a predictive conceptual model of critical zone
evolution. This limitation is primarily due to incomplete knowledge of couplings
between the physical, chemical, and biological processes in the critical zone,
including both positive and negative feedbacks and their distribution in time and
space.
An example of processes not adequately understood at present literally lies
beneath our feet. We lack observation and theory of the weathering front (the
interface between regolith and bedrock) that strongly influences processes in the
critical zone. Coupled with the rapid development of soil ecology as a distinct
discipline over the past several decades, this sets the stage for significant advances in
our understanding of how life above ground and life below ground are adapted to
each other and to spatially variable, hydrogeomorphic processes. The thin layer of
weathered rock and soil that mantles Earth's surface offers exceptional opportunities
for research on both fundamental processes shaping landscapes and applied issues
related to the geobiological basis for soil fertility. Chemical weathering and erosion
of bedrock and soil influence climate, river and groundwater chemistry, bedrock
erodibility, and ecosystem properties. Despite the fundamental importance of soil
formation and fertility for life on Earth's surface, soils and the breakdown of rock to
form soil remain among the least understood areas of the Earth sciences. Quantifying
the controls on rates of rock breakdown to form soils is needed to understand the
processes of soil formation and how they vary in different landscapes, climates, and
tectonic regimes.
Interdisciplinary studies of the critical zone are yielding new ideas about the
interactions of weathering, erosion, and biology in the critical zone. These include
hypotheses concerning the evolution of the critical zone, such as that in relatively
stable landscapes where biology drives weathering in the initial stages of plant
establishment while weathering drives biology over the long term (Brantley et al.,
2011). This work also suggests that future land use change may impact critical zone
processes more than climate change and that restoration efforts are likely to restore
hydrological functions on shorter timescales (decades or less) than biogeochemical
functions and biodiversity (Brantley et al., 2011).
A substantial investment in in situ environmental sensors, field instruments,
geochemical tools, remote sensing, surface and subsurface imaging, and development
of new technologies will be required to test these hypotheses. For example,
geochemists now possess powerful tools that permit the characterization of
fundamental processes and elemental, molecular, and isotopic properties at scales
from submicroscopic to planetary, fueled in part by tremendous advances at the
nanoscale and in computational and instrumental toolkits. Among these advances are
abilities to date processes in the critical zone at increasingly fine resolution using
cosmogenic and uranium series isotope systems.
Two interdisciplinary techniques currently supported by EAR also show
significant promise. First, geodetic techniques are increasingly being used to measure
changes in the components of the water cycle. Long-term and seasonal subsidence
can be observed via Global Positioning Systems (GPS) and Interferometric Synthetic
Aperture Radar (InSAR), providing important constraints on groundwater depletion
due to withdrawals for irrigation and municipal use. Gravity data measured using