Centre of Geographical Studies

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Detailed detection of active layer freeze–thaw dynamics using quasi-continuous electrical resistivity tomography (Deception Island, Antarctica).

Publication . Farzamian, Mohammad; Vieira, Gonçalo; Santos, Fernando A. Monteiro; Tabar, Borhan Yaghoobi; Hauck, Christian; Paz, Maria Catarina; Bernardo, Ivo; Ramos, Miguel; Angel de Pablo, Miguel

Climate-induced warming of permafrost soils is a global phenomenon, with regional and site-specific vari- ations which are not fully understood. In this context, a 2- D automated electrical resistivity tomography (A-ERT) sys- tem was installed for the first time in Antarctica at Decep- tion 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 meteoro- logical events on active layer dynamics. In addition, the feasi- bility of installing and running autonomous ERT monitoring stations in remote and extreme environments such as Antarc- tica was evaluated for the first time. Measurements were re- peated at 4 h intervals during a full year, enabling the detec- tion of seasonal trends and short-lived resistivity changes re- flecting individual meteorological events. The latter is impor- tant for distinguishing between (1) long-term climatic trends and (2) the impact of anomalous seasons on the ground ther- mal regime. Our full-year dataset shows large and fast temporal resis- tivity changes during the seasonal active layer freezing and thawing and indicates that our system setup can resolve spa- tiotemporal thaw depth variability along the experimental transect at very high temporal resolution. The largest resis- tivity 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 thaw- ing 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 investiga- tion 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 win- ter as a consequence of short-lived meteorological extreme events. These results emphasize the significance of the con- tinuous 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 monitor- ing dataset on Deception Island, we believe that this sys- tem shows high potential for autonomous applications in re- mote 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 valida- tion of heat transfer models between the active layer and per- mafrost.

2020Journal article

Open access

Communicating the Urban Experience through Biosensing: A Participatory Approach

Publication . Paiva, Daniel; Gonçalves, Ana; Ferreira, Daniela; Pedro, Tomás; Portugal, Inês Boavida

Advances in biosensing technologies have led to the commercialization of novel lightweight wearable devices, which have been praised by urban scholars for offering the possibility to quantify emotions in real-world settings, something that had proven to be very challenging until now. Although many studies mix biosensing with qualitative methods to provide a clearer picture of what physiological data might mean in terms of emotions, there has been little exploration of how people interpret their own biodata. Following calls for greater attention to participation in biosensing studies, this article explores the nuances of the interpretation of biodata by research participants. Drawing on the findings of a study in which participants were invited to reflect on and discuss their own biodata during and after a walk in a high street in Lisbon, we show how exposing participants to biodata creates moments of bounded interference that foster in-depth reflection about the urban experience. With this in mind, we discuss how bounded interference can be a generative driver for more detailed discussions about spatial experiences.

2023-04-27Journal article

Open access