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- 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.
- Active layer thermal regime in two climatically contrasted sites of the Antarctic Peninsula regionPublication . Hrbáček, F.; Oliva, M.; Laska, K.; Ruiz-Fernández, J.; De Pablo, M. A.; Vieira, Goncalo; Ramos, M.; Nývlt, D.Permafrost controls geomorphic processes in ice-free areas of the Antarctic Peninsula (AP) region. Future climate trends will promote significant changes of the active layer regime and permafrost distribution, and therefore a better characterization of present-day state is needed. With this purpose, this research focuses on Ulu Peninsula (James Ross Island) and Byers Peninsula (Livingston Island), located in the area of continuous and discontinuous permafrost in the eastern and western sides of the AP, respectively. Air and ground temperatures in as low as 80 cm below surface of the ground were monitored between January and December 2014. There is a high correlation between air temperatures on both sites (r=0.74). The mean annual temperature in Ulu Peninsula was -7.9 ºC, while in Byers Peninsula was -2.6 ºC. The lower air temperatures in Ulu Peninsula are also reflected in ground temperatures, which were between 4.9 (5 cm) and 5.9 ºC (75/80 cm) lower. The maximum active layer thickness observed during the study period was 52 cm in Ulu Peninsula and 85 cm in Byers Peninsula. Besides climate, soil characteristics, topography and snow cover are the main factors controlling the ground thermal regime in both areas.
- Evaluation of the ground surface Enthalpy balance from bedrock temperatures (Livingston Island, Maritime Antarctic)Publication . Ramos, M.; Vieira, GoncaloThe annual evolution of the ground temperatures from Incinerador borehole in Livingston Island (South Shetlands, Antarctic) is studied. The borehole is 2.4 m deep and is located in a massive quartzite outcrop with negligible water content, in the proximity of the Spanish Antarctic Station Juan Carlos I. In order to model the movement of the 0◦C isotherm (velocity and maximum depth) hourly temperature profiles from: (i) the cooling periods of the frost season of 2000 to 2005, and (ii) the warming periods of the thaw season of 2002–2003, 2003–2004 and 2004–2005, were studied. In this modelling approach, heat gains and losses across the ground surface are assumed to be the causes for the 0◦C isotherm movement. A methodological approach to calculate the ground Enthalpy change based on the thermodynamic analysis of the ground during the cooling and warming periods is proposed. The Enthalpy change into the rock is equivalent to the heat exchange through the ground surface during each season, thus enabling to describe the interaction groundatmosphere and providing valuable data for studies on permafrost and periglacial processes. The bedrock density and thermal conductivity are considered to be constant and initial isothermal conditions at 0◦C are assumed (based in collected data and local meteorological conditions in this area) to run the model in the beginning of each season. The final stages correspond to the temperatures at the end of the cooling and warming periods (annual minima and maxima). The application of this method avoids error propagation induced by the heat exchange calculations from multiple sensors using the Fourier method.
- Thermal conductivity and thermal diffusivity of cores from a 26 meter deep borehole drilled in Livingston Island, Maritime AntarcticPublication . Correia, A.; Vieira, Goncalo; Ramos, M.During the month of January of 2008 a borehole (Permamodel-Gulbenkian 1 — PG1) 26 m deep was drilled on the top of Mount Reina Sofia (275 m a.s.l.) near the Spanish Antarctic Station of Livingston Island, South Shetland Islands. Cores from 1.5 m to about 26 m deep were collected for measuring several physical properties. The objective of the present work is to report the values of the thermal conductivity and the thermal diffusivity that were measured in the cores from the borehole and the heat production that was estimated for the geological formations intercepted by it. Seven cores were selected to measure the thermal conductivity and the thermal diffusivity. The measured values for the thermal conductivity vary from 2.6 W/mK to 3.3 W/mK while the measured values for the thermal diffusivity vary from 1.1 × 10− 6 m2/s to 1.6 × 10− 6 m2/s. Both thermal conductivity and thermal diffusivity, on average, show a slight increase with depth. Average heat production was also estimated for two portions of the borehole: one from 2 to 12 m and the other from 12 to 25 m. A gamma-ray spectrometer was used to estimate the concentrations of uranium, thorium, and potassium of the cores, from which the heat production per unit volume was calculated. The estimated heat production for the first half of the borehole is 2.218 μW/m3 while for the second half it is 2.173 μW/m3; these heat production values are compatible with acidic rock types. Porosity and density were also estimated for the same cores.
- Geophysical identification of permafrost in Livingston Island, maritime AntarcticaPublication . Hauck, Christian; Vieira, Goncalo; Gruber, Stephan; Blanco, Juanjo; Ramos, MiguelThe current permafrost distribution on Livingston Island, South Shetland Islands, maritime Antarctic, was investigated using electrical resistivity tomography, refraction seismics, and shallow borehole temperatures. The field sites include different geological and geomorphological settings, including ice cored moraines and bedrock sites with debris covers of different thickness. Two-dimensional geophysical inversion schemes were used to analyze spatial heterogeneity at field sites and to detect isolated occurrences of ground ice. Results confirm that permafrost is widespread on Livingston Island, with high ice content in ice cored moraines and little in the cracks and fissures of frozen bedrock. Specific electrical resistivity values range from 10,000–40,000 ohm-m (frozen unconsolidated material) to 1500–10,000 ohm-m (frozen quartzite/shale). Combining seismic P wave velocities and specific electrical resistivities, a typical ‘‘roof-type’’ distribution was found with maximum resistivities coinciding with P wave velocities around 3000 m/s and decreasing resistivities for both increasing and decreasing velocities.