Detailed detection of active layer freeze–thaw dynamics using quasi-continuous electrical resistivity tomography (Deception Island, Antarctica)
Authors: Farzamian Mohammad , Vieira Gonçalo , Monteiro Santos Fernando A. , Yaghoobi Tabar Borhan , Hauck Christian , Paz Maria Catarina , Bernardo Ivo , Ramos Miguel , de Pablo Miguel Angel 
Published: March 2020

Abstract. Climate-induced warming of permafrost soils is a global phenomenon,
with regional and site-specific variations which are not fully
understood. In this context, a 2-D automated electrical resistivity
tomography (A-ERT) system was installed for the first time in
Antarctica at Deception Island, associated to the existing Crater
Lake site of the Circumpolar Active Layer Monitoring – South Program (CALM-S) – site. This setup aims to (i) monitor subsurface freezing and
thawing processes on a daily and seasonal basis and map the
spatial and temporal variability in thaw depth and to (ii) study the
impact of short-lived extreme meteorological events on active layer
dynamics. In addition, the feasibility of installing and running
autonomous ERT monitoring stations in remote and extreme
environments such as Antarctica was evaluated for the first
time. Measurements were repeated at 4 h intervals during
a full year, enabling the detection of seasonal trends and
short-lived resistivity changes reflecting individual meteorological
events. The latter is important for distinguishing between (1) long-term
climatic trends and (2) the impact of anomalous seasons on the
ground thermal regime. Our full-year dataset shows large and fast temporal resistivity
changes during the seasonal active layer freezing and thawing and
indicates that our system setup can resolve spatiotemporal thaw
depth variability along the experimental transect at very high
temporal resolution. The largest resistivity changes took place during
the freezing season in April, when low temperatures induce an abrupt
phase change in the active layer in the absence of snow cover. The
seasonal thawing of the active layer is associated with a slower
resistivity decrease during October due to the presence of snow
cover and the corresponding zero-curtain effect. Detailed
investigation of the daily resistivity variations reveals several
periods with rapid and sharp resistivity changes of the near-surface
layers due to the brief surficial refreezing of the active layer in
summer or brief thawing of the active layer during winter as
a consequence of short-lived meteorological extreme events. These
results emphasize the significance of the continuous A-ERT
monitoring setup which enables detecting fast changes in the active
layer during short-lived extreme meteorological events. Based on this first complete year-round A-ERT monitoring dataset on
Deception Island, we believe that this system shows high potential
for autonomous applications in remote and harsh polar environments
such as Antarctica. The monitoring system can be used with larger
electrode spacing to investigate greater depths, providing adequate
monitoring at sites and depths where boreholes are very costly and
the ecosystem is very sensitive to invasive techniques. Further
applications may be the estimation of ice and water contents through
petrophysical models or the calibration and validation
of heat transfer
models between the active layer and permafrost.