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- Registadores automáticos de baixo-custo para a monitorização de temperaturas do ar, da rocha e do soloPublication . Vieira, Goncalo; Mora, Carla; Ramos, MiguelRegistadores automáticos de temperatura do tipo Tiny Talk II® foram transformados no laboratório do Centro de Estudos Geográficos, com o objectivo de monitorizar as variações de temperatura do ar, rocha e solo. Tratam-se de registadores de 8 bits, com capacidade para armazenar até 1800 dados de temperatura medida a intervalos pré-definidos. A principal vantagem do sistema reside no baixo custo dos instrumentos, na sua pequena dimensão e na simplicidade das adaptações necessárias para que sejam medidos os parâmetros referidos. Descrevem-se na presente nota todos os procedimentos necessários para a construção dos três tipos de sistema de aquisição de dados.
- Pan-Antarctic map of near-surface permafrost temperatures at at 1 km2 scalePublication . Obu, Jaroslav; Westermann, Sebastian; Vieira, Gonçalo; Abramov, Andrey; Balks, Megan Ruby; Bartsch, Annett; Hrbáček, Filip; Kääb, Andreas; Ramos, MiguelPermafrost is present within almost all of the Antarctic's ice-free areas, but little is known about spatial variations in permafrost temperatures except for a few areas with established ground temperature measurements. We modelled a temperature at the top of the permafrost (TTOP) for all the ice-free areas of the Antarctic mainland and Antarctic islands at 1 km2 resolution during 2000–2017. The model was driven by remotely sensed land surface temperatures and downscaled ERA-Interim climate reanalysis data, and subgrid permafrost variability was simulated by variable snow cover. The results were validated against in situ-measured ground temperatures from 40 permafrost boreholes, and the resulting root-mean-square error was 1.9 ∘C. The lowest near-surface permafrost temperature of −36 ∘C was modelled at Mount Markham in the Queen Elizabeth Range in the Transantarctic Mountains. This is the lowest permafrost temperature on Earth, according to global-scale modelling results. The temperatures were most commonly modelled between −23 and −18 ∘C for mountainous areas rising above the Antarctic Ice Sheet and between −14 and −8 ∘C for coastal areas. The model performance was good where snow conditions were modelled realistically, but errors of up to 4 ∘C occurred at sites with strong wind-driven redistribution of snow.
- Detailed detection of active layer freeze–thaw dynamics using quasi-continuous electrical resistivity tomography (Deception Island, Antarctica)Publication . Farzamian, Mohammad; Vieira, Gonçalo; Monteiro Santos, Fernando A.; Yaghoobi Tabar, Borhan; Hauck, Christian; Paz, Maria Catarina; Bernardo, Ivo; Ramos, Miguel; de Pablo, Miguel AngelClimate-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. © 2020 Copernicus GmbH. All rights reserved.
- Susceptibility modelling of hummocky terrain distribution using the information value method (Deception Island, Antarctic Peninsula)Publication . Melo, Raquel; Vieira, Goncalo; Caselli, Alberto; Ramos, MiguelThe hummocky terrains of Deception Island (Antarctic Peninsula) are continuous surfaces with decimetre to metre wide and decimetre depth bumps located mainly in the lower section of sloping lapilli and scoria terrains. A detailed study site between Cerro Caliente and Crater Lake was selected for the detailed mapping of hummocky terrains and for modelling their spatial distribution according to controlling geographical factors. A model of the susceptibility of occurrence of the hummocky terrains was created using the information value method, together with five independent variables: elevation, slope, global summer radiation, total curvature and lithology. Success and prediction rate curves were used for model validation and the Area Under the Curve index was used to quantify the levels of performance and prediction. The results were of high quality with a success rate of 88% and a prediction rate of 78%. The classes of the independent variables with more relevance in the occurrence of hummocky terrains were: elevation between 20–30 m and 60–70 m; concave or rectilinear/flat areas; slopes between 8 and 12º; tuff cones and maar deposits and global summer radiation between 1.8 and 2.0 TJm− 2. The good quality of the modelling results supports its use for assessing the future potential for formation of new hummocky terrain areas, or even to estimate the spatial distribution of buried ice within the permafrost environment of Deception Island.
- Thermal state of permafrost and active-layer monitoring in the antarctic: advances during the international polar year 2007-2009Publication . Vieira, Goncalo; Bockheim, James; Guglielmin, Mauro; Balks, Megan; Abramov, Andrey A; Boelhouwers, Jan; Cannone, Nicoletta; Ganzert, Lars; Gilichinsky, David A.; Goryachkin, Sergey; López-Martínez, Jerónimo; Meiklejohn, Ian; Raffi, Rossana; Ramos, Miguel; Schaefer, Carlos; Serrano, Enrique; Simas, Felipe; Sletten, Ronald; Wagner, DirkResults obtained during the International Polar Year (IPY) on the thermal state of permafrost and the active layer in the Antarctic are presented, forming part of ANTPAS (‘Antarctic Permafrost and Soils’), which was one of the key projects developed by the International Permafrost Association and the Scientific Committee for Antarctic Research for the IPY. The number of boreholes for permafrost and active-layer monitoring was increased from 21 to 73 during the IPY, while CALM-S sites to monitor the active layer were increased from 18 to 28. Permafrost temperatures during the IPY were slightly below 08C in the South Shetlands near sea-level, showing that this area is near the climatic boundary of permafrost and has the highest sensitivity to climate change in the region. Permafrost temperatures were much lower in continental Antarctica: from the coast to the interior and with increasing elevation they ranged between 13.38C and 18.68C in Northern Victoria Land, from 17.48C to 22.58C in the McMurdo Dry Valleys, and down to 23.68C at high elevation on Mount Fleming (Ross Island). Other monitored regions in continental Antarctica also showed cold permafrost: Queen Maud Land exhibited values down to 17.88C on nunataks, while in Novolazarevskaya (Schirmacher Oasis) at 80 m a.s.l. the permafrost temperature was 8.38C. The coastal stations of Molodeznaya at Enderby Land showed permafrost temperatures of 9.88C, Larsemann Hills – Progress Station in the Vestfold Hills region – recorded 8.58C, and Russkaya in Marie Byrd Land, 10.48C. This snapshot obtained during the IPY shows that the range of ground temperatures in the Antarctic is greater than in the Arctic.
- Ground temperature and permafrost distribution in Hurd Peninsula (Livingston Island, Maritime Antarctic): an assessment using freezing indexes and TTOP modellingPublication . Ferreira, Alice; Vieira, Goncalo; Ramos, Miguel; Nieuwendam, AlexandreThe Western Antarctic Peninsula region shows mean annual air temperatures ranging from −4 to −2 °C. Due to its proximity to the climatic threshold of permafrost, and evidence of recent changes in regional air temperatures, this is a crucial area to analyse climate-ground interactions. Freezing indexes and n-factors from contrasting topographic locations in Hurd Peninsula (Livingston Island) are analysed to assess the influence of snow cover on soil's thermal regime. The snow pack duration, thickness and physical properties are key in determining the thermal characteristics and spatial distribution of permafrost. The Temperature at the Top Of the Permafrost (TTOP) model uses freezing and thawing indexes, n-factors and thermal conductivity of the ground, as factors representing ground-atmosphere interactions and provides a framework to understand permafrost conditions and distribution. Eight sites were used to calculate TTOP and evaluate its accuracy. They encompass different geological, morphological and climatic conditions selected to identify site-specific ground thermal regime controls. Data was collected in the freezing seasons of 2007 and 2009 for air, surface and ground temperatures, as well as snow thickness. TTOP model results from sites located between 140 and 275 m a.s.l were very close to observational data, with differences varying from 0.05 to 0.4 °C, which are smaller than instrumental error. TTOP results for 36 m a.s.l confirm that permafrost is absent at low altitude and thermal offsets for rock areas show values between 0.01 and 0.48 °C indicating a small effect of latent heat, as well as of advection.
- Evaluation of Envisat ASAR IMP imagery for snow mapping at varying spatial resolution (Deception Island, South Shetlands – Antarctica)Publication . Mora, Carla; Vieira, Goncalo; Ramos, MiguelAdvanced synthetic aperture radar image mode precision (ASAR IMP) scenes of Deception Island from December 2008 to September 2010 have been analysed to assess its potential for snow cover classification. Backscattering was checked against ground truth. Despite the good spatial resolution of the ASAR, its applicability for detecting snow cover, and especially wet snow, was only possible at much lower resolutions, since noise was found to be very high. Scenes with bare ground or with dry snow cover showed highest backscattering, with averages from 210 to 212 dB. Wet snow showed a shift towards lower values, peaking at 215 dB. A threshold of 213 to 214 dB was identified between dry/bare ground and wet snow scenes at Crater Lake. The backscatter difference to a reference snow-free scene usually provided better classification results, and a threshold ranging from 22 to 23 dB was found. Results show that, despite the relative ease of use of C-band ASAR, special care is necessary since the results show significant noise, and it should only be applied to large areas. Large seasonal patterns of snow melt were identified on Deception Island.
- Active layer dynamics in three topographically distinct lake catchments in Byers Peninsula (Livingston Island, Antarctica)Publication . Oliva, Marc; Hrbacek, Filip; Ruiz-Fernández, Jesús; de Pablo, Miguel Ángel; Vieira, Goncalo; Ramos, Miguel; Antoniades, DermotTopography exerts a key role in controlling permafrost distribution in areas where mean annual temperatures are slightly negative. One such case is the low-altitude environments of Maritime Antarctica, where permafrost is sporadic to discontinuous below 20–40 m asl and continuous at higher areas and active layer dynamics are thus strongly conditioned by geomorphological setting. In January 2014 we installed three sites for monitoring active layer temperatures across Byers Peninsula (Livingston Island, South Shetland Islands) at elevations between 45 and 100 m. The sites are situated in lake catchments (lakes Escondido, Cerro Negro, and Domo) that have different geomorphological and topographical conditions. Our objective was to examine the role of topography and microclimatic conditions in determining the active layer thermal regime in order to identify the factors that control geomorphic processes in these lake catchments. At each site a set of loggers was installed to monitor air temperature (AT), snow thickness (SwT) and soil temperature (ST) down to 80 cm depth. Mean annual air temperatures (MAAT) showed similar values in the three sites (−2.7 to −2.6 °C) whereas soil temperatures showed varying active layer thicknesses at the three catchments. The ground thermal regime was strongly controlled by soil properties and snow cover thickness and duration, which is influenced by local topography. Geomorphological processes operating at the lake catchment scale control lacustrine sedimentation processes, and both are dependent on the combination of topographical and climatic conditions. Therefore, the interpretation of lake sediment records from these three lakes requires that soil thermal regime and snow conditions at each site be taken into account in order to properly isolate the geomorphological, environmental and climatic signals preserved in these lake records.
- Active layer and permafrost thermal regimes in the ice-free areas of AntarcticaPublication . Hrbáček, Filip; Oliva, Marc; Hansen, Christel; Balks, Megan; O'Neill, Tanya Ann; de Pablo, Miguel Angel; Ponti, Stefano; Ramos, Miguel; Vieira, Gonçalo; Abramov, Andrey; Kaplan Pastíriková, Lucia; Guglielmin, Mauro; Goyanes, Gabriel; Francelino, Marcio Rocha; Schaefer, Carlos; Lacelle, DenisIce-free areas occupy <0.5% of Antarctica and are unevenly distributed across the continent. Terrestrial ecosystem dynamics in ice free areas are strongly influenced by permafrost and the associated active layer. These features are the least studied component of the cryosphere in Antarctica, with sparse data from permanent study sites mainly providing information related to the ground thermal regime and active layer thickness (ALT). One of the most important results of the International Polar Year (IPY, 2007/08) was an increase in ground thermal regime monitoring sites, and consequently our knowledge of Antarctic permafrost dynamics. Now, 15 years after the IPY, we provide the first comprehensive summary of the state of permafrost across Antarctica, including the sub-Antarctic Islands, with analyses of spatial and temporal patterns of the dominant external factors (climate, lithology, biota, and hydric regime) on the ground thermal regime and active layer thickness. The mean annual ground temperatures of the active layer and uppermost part of the permafrost in Antarctica remain just below 0 °C in the warmest parts of the Antarctic Peninsula, and were below −20 °C in mountainous regions of the continent. The ALT varies between a few cm in the coldest, mountainous, parts of the Transantarctic Mountains up to >5 m in bedrock sites in the Antarctic Peninsula. The deepest and most variable ALTs (ca. 40 to >500 cm) were found in the Antarctic Peninsula, whereas the maximum ALT generally did not exceed 90 cm in Victoria Land and East Antarctica. Notably, found that the mean annual near-surface temperature follows the latitudinal gradient of −0.9 °C/deg. (R2 = 0.9) and the active layer thickness 3.7 cm/deg. (R2 = 0.64). The continuous permafrost occurs in the vast majority of the ice-free areas in Antarctica. The modelling of temperature on the top of the permafrost indicates also the permafrost presence in South Orkneys and South Georgia. The only areas where deep boreholes and geophysical surveys indicates discontinuous or sporadic permafrost are South Shetlands and Western Antarctic Peninsula.
- The permafrost environment of northwest Hurd Peninsula (Livingston Island, maritime Antarctic): preliminary resultsPublication . Vieira, Gonçalo; Ramos, Miguel; Gruber, S.; Hauck, C.; Blanco, J.The permafrost spatial distribution in Hurd Peninsula (Livingston Island, Antarctic) and its thermal state are the focus of the ongoing research. A multidisciplinary approach that includes meteorological and ground temperature monitoring, geomorphological mapping and geophysical surveying has been used. The results from this research indicate that ice-cored moraines and active rockglaciers are present down to sea-level. Permafrost in bedrock is more difficult to assess. It is present at 275m ASL in Reina Sofia Hill, with an active layer ca. 1m deep. At 100m the Electrical Tomography Resistivity data suggests that permafrost is present, at least under snow patches. At 35m ASL in bedrock permafrost hasn’t been found. However, more research is needed for assessing the spatial distribution of permafrost. Drilling and borehole temperature monitoring are the main objectives of the next Antarctic campaigns.
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