Foreword to this Special Issue on Climate Change and the Critical Zone Geophysics

Welcome to this special issue on the use of geophysics in climate change and critical zone (CZ) research.  The importance of these research areas cannot be overstated, and yet when we were selecting contributions for this special issue, we wrestled with the fundamental question: are climate change and the critical zone two separate research areas, or one?  In other words, would there be a clear distinction between critical-zone focused articles and those addressing climate change, or would there be significant overlap making that distinction irrelevant. As we worked through the excellent submissions, it became more and more clear that any geophysical study addressing one of these elements would almost certainly be impacted in some way by the other. 

Let us consider the definition of the Critical Zone:

“The Critical Zone is a dynamic system that extends from the top of the canopy to the bottom of groundwater aquifers. This zone includes the land surface, vegetation, and water bodies where a series of systems and processes interact and is the most heterogeneous portion of Earth.” – Society of Exploration Geophysicists (SEG) Wiki 

From that definition, it is clear that any application of near-surface geophysics—whether addressing climate change or otherwise—will inherently intersect and be influenced by the CZ. However, we find there is one notable piece missing from this definition: the cryosphere. We suggest an updated definition to include ice and snow as part of the CZ. This point is particularly relevant to this issue, as geophysical applications to the cryosphere are one of the fastest-growing research areas, largely motivated by climate change impacts. 

Accordingly, we posit the term cryogeophysics is emerging as a valuable addition to the lexicon and worth consideration within the near-surface community. While this term has been used infrequently, we suggest more widespread adoption would be worthwhile, along with clear agreement on the definition. We suggest this term, like many other geophysical subdisciplines, encompasses the varying approaches for cryosphere-based geophysical investigations, embracing the historical accomplishments within the field, and this definition provides a clear classification for this growing discipline moving forward. We venture an official definition might result in something like: 

“Cryogeophysics is a cross-disciplinary area of research that uses near-surface geophysical sensing technologies and methods for the purpose of understanding, monitoring, and/or characterizing cold-region environments—ranging from polar and arctic/subarctic to alpine settings—including studies of permafrost, glaciers, ice sheets, sea ice, snow, and seasonally frozen ground.” 

With a subdiscipline so integral to the future of our planet, we believe it warrants a moniker equally as valuable and encompassing.  Many of the papers presented in this issue highlight the diversity and unique expertise needed for cryogeophysics applications.

The content we have for you in this special issue is very exciting, with a mix of traditional near-surface geophysical methods, as well as those at the forefront of their fields, all aimed at solving climate change and critical zone problems. These articles cover a broad range of targets and objectives, from scientific and methodological advancements to unique and impactful human-interest research. It is our pleasure to present to you the following geophysical research with far-reaching global impact in both critical zone and climate change research.  

In this issue, you will find multiple papers highlighting the connection between geophysics, climate change, and communities. First, a paper where ground-penetrating radar (GPR) was used to map marked and unmarked graves near a church by the Alaskan village of Karluk, where coastal erosion is forcing relocation of the church. Second, an article summarizing the adaptability of towed transient electromagnetic (TEM) systems for addressing a variety of problems. The authors demonstrate the use of TEM in water availability studies in Tanzania and Greenland, and a lake and aquifer system study in Denmark helping the town understand how the system responds to rising water levels. A third paper summarizes recent findings from a unique waterborne gradient self-potential method used for identifying surface water and groundwater exchanges along rivers within a transboundary aquifer system. 

Additionally, several papers address advances in seismic technology and processing techniques for climate and critical-zone research. One paper demonstrates the feasibility of snow-coupled distributed acoustic sensing (DAS) as an intrusion detection system for displaced polar bears at research camps in Greenland. Another paper uses DAS on dark-fiber beneath the Arctic Ocean to explore coastal processes and the influence of changing sea ice coverage. An additional article explores the cryosphere applications of seismic horizontal-vertical spectral ratios (HVSR) through estimations of glacier thickness and monitoring permafrost dynamics. 

Lastly, several papers apply geophysical methods towards understanding connections between carbon cycling, hydrology, and permafrost variability. One paper details the interrelationships between physical, thermal, hydrological, and biogeochemical processes at two end-member permafrost sites in Alaska using electrical resistivity tomography (ERT), frequency-domain electromagnetic induction (EMI), GPR, unmanned aerial systems (UAS), and distributed temperature profiling (DTP). In a separate paper, GPR was used to identify the geologic controls on hydrology and carbon-cycling in boreal peatlands in Maine. And finally, we present an article summarizing the value of airborne electromagnetic (AEM) datasets for regional-scale subsurface characterization, particularly in the heterogeneous permafrost regime, demonstrated through a series of case-study examples.

We hope you enjoy this issue as much as we enjoyed assembling the content.

Best,

Dan R. Glaser & Stephanie R. James

Guest Editors FastTIMES Special Issue on Climate Change and the Critical Zone