Ninth International Conference on Permafrost ... - IARC Research

A Method for the Analysis of the Thermal Permafrost DynamicsM.A. Hidalgo, J.J. Blanco, M. Ramos, D. ToméPhysics Department, University of Alcala, SpainG. VieiraCentre for Geographical Studies, University of Lisbon, PortugalIntroductionAntarctica is one of the most sensitive areas to climatechange in the world. This is close to the upper limit forpermafrost viability and, therefore, studying the distributionand the state of the permafrost, we can monitor climateevolution. Livingston Island (62°39′S, 60°21′W – SouthShetland archipelago) is located 50 km west of the AntarcticPeninsula. Almost 90% of the island is glacierized, andthe rest has a seasonal snow cover, coinciding with theperiglacial domain.Experiment DescriptionThe Incinerador borehole drilled in quartzite bedrock hasa depth of 2.4 m with a diameter of 90 mm. There is a loggerchain inside the borehole pipe. Since January 2004, thechain is composed of 6 loggers placed at different depths:5, 15, 40, 90, 150, and 230 cm. The time interval betweenconsecutive measurements is 1 hour and the accuracy of thedataloggers (tiny talk Gemini Co.) is 0.2°C.Data AnalysisIn Figure 1a, we show the temperatures at the differentdepths mention above recorded during the year 2005 as afunction of the day of year (doy).Previous to the FFT analysis, a detrending process overthe data corresponding to every record was made (Fig. 1b).After that, the FFT power spectrum obtained is shown inFigure 2.Model DescriptionThe study of the permafrost and thermal regime ofthe active layer require the knowledge of their thermaldiffusivity. This parameter is the key to understanding thethermal response of the soil—in particular, the exponentialattenuation of the temperature wave with depth and the lagin phase. (In all the presented study, we assume that there areno thermal sources along all the depths considered).800PS Amplitude (x 1000)60040020000.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7ν (h −1 )80808PS Amplitude (x 1000)604020PS Amplitude (x 1000)604020PS Amplitude (x 1000)64200.10 0.11 0.1200.40 0.41 0.42 0.4300.55 0.56 0.57 0.58 0.59 0.60Figure 1. Temperatures recorded during the year 2005 at thedifferent depths (indicated with the legend insert): (1a) the originaldata, (1b) the data after detrending.ν (h -1 )Figure 2. Power spectrum from the FFT analysis made over thedetrending data of Figure 1b: (2a) the power spectrums in all thefrequency range for the different depths (the colour legends arethe same as in Figure 1; (2b)–(2d) details at different frequencyranges.ν (h -1 )ν (h -1 )97