High-resolution geophysical observations and modeling of the cryosphere using distributed optical fiber sensing

Abstract

Glaciers and ice sheets are projected to rapidly decline in volume and contribute significantly to sea level rise in the coming centuries due to anthropogenic climate warming. The risk to fresh water availability in coastal infrastructure are great; however, our understanding of how glacier melt and ice discharge vary over space and time is limited. Current conventional instrumentation for sensing glacier and ice sheet change due to melt or ice discharge can be classified into two categories: remote sensing and in situ instrumentation. Remote sensing platforms have the benefit of a large aperture, but often are limited in revisit times and resolution. In situ instrumentation, however, can make continuous measurements of glacier change limited only by the labor to deploy a network of sensors and the sensor robustness. This motivates the search for novel methods for sensing of glacier melt and flow that bridges the gap between aperture and spatiotemporal resolution. Here, I leverage distributed optical fiber sensing, namely distributed acoustic sensing and distributed temperature sensing. Both systems allow for meter scale sampling of the acoustic or temperature fields continuously along a fiber optic cable with collection duration times of months if not longer. In the following chapters, I utilize distributed optical fiber sensing techniques to make novel observations of glacier melt and ice sheet flow. Using a fiber cable deployed along the entire flow line of Rhonegletscher in Switzerland, I calculate the spatiotemporal variability of the supraglacial seismo-acoustic wave field amplitude. I first show that the supraglacial seismo-acoustic wave field is a function of the amount of meltwater runoff and use this relationship to infer proglacial discharge. Following from this work, I deployed fiber optic cables in boreholes drilled in the Allan Hills Blue Ice Area, Antarctica. Here, I show how borehole temperatures record climate in the blue ice area and model ice flow that reveals mechanisms for preserving ancient ice. Finally, I perform a passive seismic survey at the Eastwind Glacier grounding line, Antarctica and reveal passive seismic reflections from the grounding line. I use the seismic reflections to recover a reflection coefficient and infer grounding line material properties. Through this work, I demonstrate the power of distributed optical fiber sensing systems for seismic and temperature sensing over large spatial and temporal baselines on glaciers. Furthermore, I add new insights into how the surface of glaciers change throughout a melt season, different mechanisms for preserving old ice that operate in a blue ice area, and Antarctic grounding line properties using observations of never before seen passive seismic reflections. This work opens the door to the possibility of monitoring highly dynamic and sensitive glacier environments as glaciers begin to respond to climate change.