Download Emerging scientific challenges at the interface of surface and deep

Emerging scientific challenges at the interface of surface and deep Earth processes:
Part 2- Cryosphere and Orogenesis research needs over next 5-10 years
Submitted by IRIS Grand Challenge Committee on Change and Interactions among Climate, Hydrology, Surface
Processes and Tectonics
Sridhar Anandakrishnan, Julie Elliott, Sean Gulick*, Eric Kirby*, Victor Tsai, Kelin Whipple (*Committee Co-chairs)
Summary statement
Understanding interactions among climate, hydrology, surface processes, and tectonics is an emerging
scientific challenge at the interface of surface and deep Earth processes. These interactions lie at the
interface of disciplines, some core to SAGE and GAGE, and some peripheral. Thus there is a clear need
for partnership with core science disciplines – the geologic record and numerical simulations both bring
a temporal dimension that extends the modern observational timescale. There is also a vital role for
discovery-based science, such as recent breakthroughs in acoustic monitoring of sediment transport qnd
ice shelf/ocean wave coupling; such processes may perhaps have been missed without “defocused”
deployments. Given the advancement of a number of recent novel use of data from observatories and
long term deployments, there is an opportunity in designing deployments to capture, not avoid, noise.
Scientific issues
Cryosphere
1. Measuring and understanding the response of the solid earth to change in glacier loading.
The history of ice volume change is poorly constrained, particularly in Antarctica. Projecting volume loss
and sea level changes into the future requires that the rate of historical changes, and the controls on
those rates, be better understood. Glacial Isostatic Adjustment (GIA) is influenced by three different
processes and Earth properties; the history of glacier change, the rheology and thicknesses of the
lithosphere, and the viscosity structure of the mantle. Estimating the first of these requires precise
constraints on the latter two. Moreover, the heterogeneity of lithospheric and mantle properties in
polar regions is poorly known, and could have significant impacts on our reconstructions of ice history.
Finally, both viscous and elastic response to glacial loading and unloading result in stress changes in the
crust, which can, in turn, lead to changes in seismicity along both active faults and crustal anisotropy.
2. Glaciers and ice sheets are dynamic at time scales ranging from centuries down to as short as
tidal cycles. The realization of the high sensitivity of glaciers to small changes in external forces and
conditions has been, in part, due to the improvement in measurement capability of surface velocities
and subglacial properties. In order to adequately treat these dynamic processes in numerical ice sheet
models, we require considerably better spatial and temporal measurements of critical parameters such
as subglacial and grounding line sedimentary structure and processes, heat flow, englacial parameters
such as temperature, crystal orientation fabric, and supraglacial parameters such as flow speed, stressconcentration, fluid flow, etc. Many of these measurements are within reach within the next decade.
3. The ocean interacts with polar ice sheets in complex ways, often to the detriment of the ice.
In a warming world, ocean circulation is an efficient way to transport heat to the ice sheet. These
processes take place beneath ice shelves and at the so-called grounding line where the ice goes afloat
either forming ice shelves or a calving front. Monitoring the change in the configuration of the ice
shelves and grounded ice can be done by networks of GPS and seismic systems that are currently sparse
and inadequate in polar regions but could be instrumental in understanding perhaps the most critical
linkage influencing the stability of ice sheets. Imaging and benchmarking modern as well as past glacial
advance-retreat events as monitored or recorded in the rock record can provide an assessment of rates,
driving forces, and potential critical exacerbating or mitigating factors.
Orogenic systems
At the time and length scales associated with the evolution of orogenic systems, advancing
understanding of the coupling between climate, erosion, and topography has two fundamental
components where IRIS facilities will play a critical role: (1) appropriate long-term observations of
lithospheric structure, the distribution of seismicity, and sedimentary basin architecture in and around
active mountain belts, and (2) advances in our understanding of the fundamentals of the underlying
processes of weathering, transport, erosion, and deformation. A few examples of how geophysical
methods and IRIS facilities can play an essential role in these efforts have been briefly highlighted above.
In addition to the above focus on records and processes of crustal deformation, there is a blossoming of
interest and capabilities in studies of large-scale surface deflections driven by changes in mantle
buoyancy and surface tractions induced by mantle flow over geologic time. A vibrant new transdisciplinary field is emerging that integrates structural seismology, mantle convection models,
lithospheric geodynamics, surface processes, and geologic records of paleoaltimetry (paleoshorelines,
erosional unconformities, accommodation space generation, paleobotany, and isotopic records).
Important uncertainties remain in interpretation and integration of structural seismic images into
mantle convection models (differentiating chemical and thermal effects on wave speeds and buoyancy),
characterization of the Earth’s viscosity structure, and magnitude of plausible dynamic topography. The
fact that accurate geologic, geomorphic, and isotopic records of surface uplift and subsidence have the
potential to provide some of the most stringent constraints on deep Earth processes and viscosity
structure gives testimony to the integrative, trans-disciplinary nature of this endeavor.
What is needed?
•Integrated observations and nested imaging at the glacier-substratum, grounding line, and the iceocean boundaries Progress has been made in linking dynamic processes at tidewater glaciers (with and
without ice shelves) to distinct seismic signals, but these linkages have not been documented across a
large number of glaciers due to a lack of adequate instrumentation. Evaluating the role each factor
plays in ice dynamics will require a combination of denser arrays of geophysical instruments in glaciated
regions both polythermal and polar, seismic profiles and ice-penetrating radar to image glacier bed
geometry and material properties, geodetic imaging and GPS data to monitor variations in ice velocity,
and fjord/marine studies at the grounding line to understand timescales and rates of processes.
Determining whether there are seismic or geodetic signals of specific sub-glacial or end-glacial processes
could lead to breakthroughs in understanding dynamics of glacial behavior such as surges, catastrophic
retreat, as well as controls on stability of ice sheets and outlet glaciers. To achieve these, however,
requires a substantial expansion of the existing geophysical and geodetic equipment pool dedicated to
polar studies.
•Orogenic scale studies of tectonics, climate and surface processes Understanding orogenesis requires
quantifying erosion, determining effects of changing climate, studying tectonic and mantle feedbacks,
and calibrating integrative models of the system. Advances are needed in understanding roles of rock
strength, river floods, glacial dynamics, precipitation, and sediment transport mechanisms on erosion.
Multi-scale studies are needed temporally to understand influences of orbital forcing, orographic
effects, changing ice and sediment loads, tectonic forcing/feedback and mantle dynamics that influence
the crust and surface. Clear opportunities exist in both nested imaging of modern systems, monitoring
of active surface and tectonic processes, and modeling interactions. These require regional studies
using seismology and geodesy and partnerships with a range of other communities and their field or
laboratory measurements.