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PROPERTIES OF FROZEN AND THAWED SOILS, BAYDARATSKAYA BAY COAST, KARA SEA: VARIABILITY AND TRENDS

Daria Aleksyutina

Abstract

The Arctic coastal zone is very sensitive to environmental changes and anthropogenic impacts. The western part of the Russian Arctic is well studied because there is a lot of petroleum-gas deposit mines, especially on the Yamal peninsula, however data about the soil properties of the coastal zone does not appear much in the published literature. This is because people who investigated in the coastal dynamics do not study the soil properties, and vice versa, those working in the geoengineering survey do not publish their results. To provide forecasts of permafrost state and conditions, knowledge of soil properties is required as the input parameters for numerical modeling and calculations. This work con?ideres the variabilities and interdependencies between the properties of frozen and thawed soils, obtained on a representative key plot on the southern Kara Sea coasts, on a 10-kilometer-long coastal segment between Levdiyev and Torasavey islands. The area of investigation was situated within continuous permafrost zone, with annual ground temperature of -4.3 ?C. Interbedded silty clays, silts and silty sands composed coastal cliffs. The main soil parameters, such as moisture, density, grain size composition, organic matter content and soil salinity, were determined using standard methods. Unfrozen water content for frozen samples and thermal properties in frozen and thawed state were also studied. Thermal properties were studied according to 3 approaches, including first type regular mode method (known as a-calorimeter) and transient heated needle methods using different devices (MIT-1 and KD2 Pro). Unfrozen water content was investigated with the help of contact and cryoscopic methods in the range of negative temperatures. It was established that peats and soils with high organic matter content were characterized by higher moisture and lower density. These soils comprised the upper part of the geological sections of the low terrace, down to 3 meters depth. Saline samples below 3 m have marine genesis. The samples? moisture varied from 10 to 205% and their density varied from 1.15 to 2.05 g/cm3. Unfrozen water content varied greatly depending on grain-size distribution; the highest values were typical for saline soils and peats. Variability trends in thermal properties were estimated, depending on temperature, moisture, density, salinity and organic content. In frozen soils, higher influence of salinity on thermal properties was typical; peat content determined thermal properties for thawed state. Based on key plot investigation, we tried to obtain robust data to evaluate trends and create models to predict conditions of the permafrost coastal zone for western part of the Russia Arctic.

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