THE RATE OF GROUND THAWING IN RELATION TO ATMOSPHERIC CONDITIONS AND TEMPERATURE ON KAFFIOYRA (NW SPITSBERGEN) IN THE SUMMER OF 1985

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1 Marek Kejna Institute of Geography, N. Copernicus University, Toruń, Poland Wyprawy Geograficzne na Spitsbergen UMCS, Lublin 1991 THE RATE OF GROUND THAWING IN RELATION TO ATMOSPHERIC CONDITIONS AND TEMPERATURE ON KAFFIOYRA (NW SPITSBERGEN) IN THE SUMMER OF 1985 INTRODUCTION Thawing intensity and depth depends 011 the amount of heat that reaches permafrost roof. Sun radiation is the source of heat for the ground. It is diminished by the albedo coefficient, and the heat that is generated during water phase reverses, or even during advection of air masses that are warmer than the ground. The size of the heat stream that reaches permafrost depends on the heat properties of the ground layers above it, i.e. mineral composition, heat capacity, and heat conductivity. Time of the heat stimulus action and thickness of the active layer exert their influence as well. With the increase of depth more and more heat is absorbed for the warming up of ground surface layers, and not for the process of permafrost degradation. All the papers on ground thawing stress the importance of atmospheric factors. Spatial differentiation of the depth and rate of ground thawing results from extraatmospheric factors connected with the physical and thermal properties of the ground, i.e. its mineral composition (Grześ, 198), ground moisture contents (Pietrucień, Skowron, 1987; Marciniak et al., 1981, 1988, 1990), exposition (Repelewska-Pękalowa et al., 1988; Marciniak, Przybylak, 1990), plant cover (Czeppe, 1966; Baranowski, 1968; Jahn, 1982; Marciniak et al., 1983; Repelewska-Pękalowa et al., 1988), snow cover (Migała, 1988), ice contents in the ground (Migała, 1989). As there are no quantitative data on the subject, there is a need for studying the direction and extent of dependence of the thawing rate on atmospheric factors, as well as for the determination of delay (in days) that exists from the moment of heat inflow (after intensive sunshine) to the beginning of the increased permafrost degradation. In order to determine the above mentioned factors, systematic, everyday measurements of the active layer thickness on the sandy-gravel, accumulative sea plain (1.68 m above the sea level) devoid of any plant cover were conducted during the 8th Toruń Polar Expedition on Kaffióyra (NW Spitsbergen) during 267

2 the period from June 26th to Aug. 8th. The impact method used allowed for the measuring accuracy of 1 cm. In order to eliminate measuring errors each measurement was repeated three times on the vertices of the triangle in which the temperature measuring site was situated. The mean values of these three measurements were used for the calculations of the rate of permafrost degradation. Attempts to relate atmospheric factors to the rate of ground thawing by means of the Pearson's coefficients of linear correlation were undertaken. Non-significant values of these coefficients made the present author consider those relations that take time delay into account. Measurements and observations were carried out every 6 hours, at 1:00, 7:00 a.m. and at 1:00, 7:00 p.m. LMT, together with the recording of sunshine, temperature and air moisture contents. Ground temperature was measured by means of elbow thermometers up to the depth of 50 cm. METEOROLOGICAL C O N D I T I O N S Weather conditions on Spitsbergen are highly variable because of the atmospheric circulation during summer that is influenced by a quasi stationary high pressure with the center over the Barents'Sea and cyclones that cyclicly travel along the coast of the archipelago (Baranowski, 1977). Advection from the North in the region of Kaffióyra brings some clouds (anticyclonal circulation), whereas the inflow of air masses from the south is often connected with cyclonal advection an increase in the cloud cover (Leszkiewicz, 1977). Cyclic changes in the cloud cover and sunshine distribution cause impulsive influence of radiation factors on the ground thermal properties and ground thawing rate. In the summer of 1985 there appeared high relative sunshine (29.8%); 65.5 hours of sunshine in all. But there were also periods with complete cloud cover (1st decades of July and August) and days with the sunshine up to 100% (June 30th, July 21st and 22nd) Tab. 1, Fig.l. High sunshine level influenced ground thermal properties: the highest 2-hour mean values were recorded in the 2nd and 3rd decades of July (July 21st, at the depths of: 1 cm 17.9 C, 5 cm 15.2 C). The heat gathered at the surface gradually penetrated deeper layers up to the permafrost roof. Heat balance, especially in the case of surface ground layers, depends on the air temperature that, in turn, depends not only on the radiation factors but also on advection. The summer of 1985 was characterized by high air temperatures (mean temp. 5. C) and mean 2-hour temperature values exceeding 10 C (on the 29th of July 11.9 C). Rainfall level in this period was exceptionally low (22.6 cm in all during the 268

3 whole study period), hence with high ground temperatures a considerable drying of the surface layers was observed (Kejna, Dzieniszewski, in press). GROUND THAWING The process of ground thawing on Spitsbergen can take place all year long if the temperature on the ground surface is above 0. 2-hour mean air temperature of 0 C, as it has been suggested in some papers, do not seem to be a sufficient criterion for the beginning of the process of ground thawing. Snow cover appearing on Spitsbergen from October to May or even June is a significant hindrance. There is no thawing under snow cover even if its thickness is small and air temperature is above zero. The process of summer formation of the active layer undergoes three phases (Fig. 1): The I phase permafrost degradation goes very quickly and reaches deeper and deeper layers; the rate of degradation depends on the external conditions (radiation balance, air temperature and the like) and the absorption abilities of the ground, as well as its heat conductivity that largely depends oii the water contents; percolating water transfers heat from the surface layers, and increases heat conductivity of the ground; Ice present in the ground is an obstacle in this process. Ice contents is closely related to the ground water balance, as well as summer and autumn rainfalls when the ground is not frozen and can absorb water. In 1985 when the measurements were starting (June 26th) ground was thawed up to the depth of 6 cm, and in the end of the I phase (July 31st) up to 97 cm. The II phase the rate of ground thawing decreases with the increasing depth. The stream of heat that flows through the ground is absorbed for warming up the layers above, and less and less heat reaches the ice horizon; balance is reached and the level of permafrost stabilizes. The balance is very unstable, and any changes in the cloud cover, sunshine or air temperature cause disturbances such as undulation. The depth of thawing reaches its maximum level of 106 cm on Aug. 20th. It is the highest measured thickness of the active layer at this site measured during all the Toruń Polar Expeditions to Kaffiorya (Wójcik et al., 1990). The III phase with the decreasing sunshine and lower air temperatures, thermal balance of the ground layers above the ice horizon is disturbed, and freezing from below starts. When temperatures below zero are predominant on the ground surface freezing from the surface downwards also takes place (double curtain effect). 269

4 THE RATE O F G R O U N D T H A W I N G The highest rate of permafrost degradation takes place in the beginning of the thawing period when the energy absorbed by the ground is mostly used for the ground ice thawing. Because of the heat losses while warming up the layers above it, the process should be slowing down with the increasing depth. The analysis of data, however, shows that the intensity of thawing during the I phase is from 1 to 3 cm/day (1.2 cm/day on the average) Fig. 1. It results from the increasing effects of atmospheric factors (mainly the increase of air temperature). This trend towards intensive thawing lasts till the end of July, which confirms earlier results (Wójcik et al., 1990). In August (the II phase) with decreasing amounts of heat (less intensive sunshine and lowering of air temperatures) the rate of thawing also decreases (0.32 cm/day on the average). The III phase started in 1985 after the maximum was reached on Aug. 20th. When autumn monotherm was stabilized in the ground gradual cooling down of the ground and freezing of the deepest layers at the rate of 0.27 cm/day takes place. When comparing the rate of permafrost degradation and the course of external factors it may be observed that the rate of degradation largely depends on the cloud cover, sunshine and air temperature Fig. 1. However, this relation, appears with a certain delay. In order to calculate this delay Pearson's coefficients of correlation were used. First, parallel data were applied (0 days of delay), and then data taking a delay of up to 7 days into account were compared Tab. 2. The values of the coefficients obtained, despite the inaccurate method of measurement taking, are high and have a stable tendency with the changing delay. As during the phases II and III when the active layer had the thickness of 1 m, no observable changes in the depth of the permafrost deposition appeared, theinfluence of the atmospheric factors on the rate of ground thawing was shown for the phase I (June 26th to July 31st). The calculated coefficients of correlation clearly show that cloud cover, sunshine, and a derivative of these two, i.e. air temperature, determine ground thawing Fig. 2. The influence of cloud cover on thawing can be noticed after -5 days, the values of the coefficients of correlation have the highest values (r = -0.61). A similar situation takes place in the case of sunshine; after 3- days with many hours of sunshine, an increased degradation of the permafrost is observed (the maximum value of r = 0.60 with the -day delay). Strong relation with the air temperature was also observed as its correlation with permafrost degradation rate was as high as The rate of thawing is related to the changes in the ground thermal properties. Depending on the layer that is compared with the rate of degradation, it appears that the closer the layer studied to the ice horizon, the shortest the delay is; e.g. the strongest relation for the ground surface appeared with a 3-day delay, and for the layer of 50 cm, after 2 days, even though the coefficient values decrease (for? the layer of 1 cm г = 0.65 cm, and for the 50 cm layer r = 0.2). 270

5 CONCLUSIONS The data presented clearly show that atmospheric factors are decisive for the rate of the process of ground thawing. Especially high values of the coefficients were observed in the case of cloud cover and sunshine (indirectly for the radiation factors). The influence appears with a 3- day delay (this amount of time is necessary for the heat coming from the sun radiation to reach the ice horizon). A similar dependence was also noticed for the air temperature, hence air temperature can also be treated as a factor that determines ground thawing rate. An increase of the active layer thickness weakens and obscures the influence of external factors, hence the values of the calculated coefficients for the I phase (June, 26th to July, 31st) reach the level of 0.6 for the cloud cover and sunshine, and 0.55 for the air temperature, whereas for the whole study period (June 26th to Aug. 31st) they do not exceed r = 0.3. The rate of thawing depends on the amount of heat that resides in the ground, hence the coefficients of correlation, when a 3-day delay was taketi into account, are as high as 0.65 for the 1 m layer, and 0.2 for the 50 cm layer. Obviously, the results obtained are typical for the studied measuring site, i.e. sandy-gravel beach, and for the specific weather, thermal, and moisture conditions that existed in the studied ground during the summer of Hence, the results presented above should be treated as an attempt only as they need further verification on different study location and at different weather conditions. Translated by Ewa Gnyp REFERENCES Baranowski S., 1968 Termika tundry peryglacjalnej SW Spitsbergen Acta Univ. Wratislav. Nr 68. Baranowski S., 1977 Subpolarne lodowce Spitsbergenu na tle klimatu tego regionu, Acta Univ. Wratislav., No 393. Czeppe Z., 1966 Przebieg głównych procesów morfogenetycznych w poludniowo-zachodnim Spitsbergenie - Z. nauk. UJ, ser. 13. Grześ M., 198 Charakterystyka warstwy czynnej wieloletniej zmarzliny na Spitsbergenie XI Sympozjum Polarne, Poznań. Jahn A., 1982 Soil thawing and active layer of permafrost. Results of investigations of the Polish Scientific Spitsbergen Expeditions Acta Univ. Wratislav Kejna M., Dzieniszewski M. (in press) Warunki meteorologiczne na Kaffioyra (NW Spitsbergen) w okresie г. A U N C, Geografia. Leszkiewicz J., 1977 Meteorological conditions in the northern part of Kaffioyra Plain during the period from July 1 to August 31, 1975 A U N C, Geografia 13, z. 3. Marciniak К., Przybylak R., 1990 Spatial differentiation of the depth of summer ground thawing in northern part of Kaffioyra (NW Spitsbergen) in 1982 and 1989 Wyprawy Geograficzne na Spitsbergen, UMCS Lublin. 271

6 Marciniak К., Przybylak R., Szczepanik W., 1981 Letnie odmarzanie gruntu na Kaffióyrze (NW Spitsbergen) VIII Sympozjum Polarne, Sosnowiec. Marciniak K.. Przybylak R., Szczepanik W., 1988 The dynamics of summer ground thawing in the Kaffioyra Plain (NW Spitsbergen) V International Conference on Permafrost, Trondheim, vol. 1. Marciniak К., Szczepanik W., 1983 Results of investigations over the summer ground thawing in the Kaffioyra (NW Spitsbergen) A U N C, Geografia 18. z 56. Migała К., 1988 Wpływ pokrywy śnieżnej na warstwę aktywną zmarzliny w rejonie Hornsundu, SW Spitsbergen XV Sympozjum Polarne, Wrocław. Migała K., 1989 Klimatyczna determinacja poziomu aktywnego zmarzliny w rejonie Hornsundu, SW Spitsbergen XVI Sympozjum Polarne, Toruń. Niedźwiedź Т., 1987 Wpływ cyrkulacji atmosfery na temperaturę powietrza w Hornsundzie, Spitsbergen XIV Sympozjum Polarne, Lublin. Pietrucień C., Skowron R., 1987 Wpływ zjawisk wodnych na głębokość rozmarzania gruntu na Ziemi Oscara II (NW Spitsbergen) XIV Sympozjum Polarne, Lublin. Repelewska-Pękalowa J., Gluza A.F., Pękała K., 1988 Wpływ lokalnych czynników na miąższość i termikę czynnej warstwy zmarzliny na Calypsostrandzie (rejon Bellsundu, Zachodni Spitsbergen) XV Sympozjum Polarne, Wrocław. Repelewska-Pękalowa /., Paszczyk J., 1990 Dynamics of permafrost active layer based on the statistical analysis Wyprawy Geograficzne na Spitsbergen, U M C S Lublin. Wójcik G., Marciniak К., Przybylak R., Kejna M., 1990 A dynamics of summer ground thawing due to meteorological conditions on the basis of Kaffioyra Plain studies (NW Spitsbergen) in the period Wyprawy Geograficzne na Spitsbergen, U M C S Lublin. STRESZCZENIE Tempo odmarzania gruntu zależy od czynników atmosferycznych oraz od właściwości cieplnych warstw zalegających nad zmarzliną zdolności pochłaniania i przewodzenia ciepła przez grunt. Wpływ czynników atmosferycznych na tempo odmarzania gruntu wykazano przy pomocy współczynników korelacji liniowej Pearsona uwzględniając opóźnienie czasowe (do 7 dni) tab. 2. Lato 1985 r. na Kaffioyra odznaczało się zmiennymi warunkami pogodowymi (tab. 1), co powodowało impulsywne oddziaływanie czynników atmosferycznych na termikę gruntu i tempo odmarzania gruntu rys. 1. Głębokość odmarzania gruntu mierzono codziennie metodą udarową na piaszczysto-żwirowej akumulacyjnej równinie nadmorskiej (Kaffioyra, N W Spitsbergen). Uśrednione wyniki z trzech pomiarów stały się przedmiotem dalszej analizy. Proces odmarzania gruntu przebiega w trzech fazach, charakteryzujących się różnym tempem degradacji zmarzliny. Najintensywniejsze odmarzanie występuje w I fazie niewielka miąższość warstwy odmarzniętej nad horyzontem zmarzliny. W miarę wzrostu miąższości warstwy czynnej tempo odmarzania maleje (II faza). Po osiągnięciu maksymalnego odmarznięcia rozpoczyna się III faza powolne wychładzanie i zamarzanie gruntu. Wpływ czynników atmosferycznych zaznacza się najsilniej przy małej miąższości odmarzniętego gruntu, stąd też do analizy przyjęto okres od 26 czerwca do 31 lipca I faza. Uzyskane współczynniki korelacji (tab. 2) wykazują dużą zależność odmarzania od stopnia zachmurzenia, usłonecznienia i temperatury powietrza. Najistotniejsze związki występują po 3- dniach opóźnienia tyle czasu potrzebne jest na dotarcie impulsu ciepła lub chłodu do stropu zmarzliny. Wartości współczynników korelacji są wysokie: dla zachmurzenia, 0.60 dla usłonecznienia i 0.55 dla temperatury powietrza rys. 2. Tempo odmarzania zależy od ilości ciepła jaka znajduje się w gruncie, stąd też współczynniki korelacji po uwzględnieniu 2-3-dniowego opóźnienia sięgają 0.65 dla warstwy 1 cm i dla 50 cm r =

7 Table 1. Mean values and sums pentade of the choosen meteorological elements and temperature of the ground and ground thawing in the Kaffióyra (NW Spitsbergen) in the period since 26th June to 31th August, U С СО-ЮЗ H o u r s P e r i od Ti C OS о i lo. о Д О OS OS eki9^ O' , 5 в ' 8й О Р mm Tgso С , ; 6. I С9 1 О. О О 5. i1 3. о. о о. о А1* cm Тг. cm/day О О. 6 о О , 6 1,6 2. О ЮЗ ' , 1. О. О. -О. О. 106.О-в О ' C-eIoudiness, U-sunshine duration, Ti-air temperature, P-preci pi tation, T g t - t e m p e r a t t i r e of t h e g r o u n d a t t h e d e p t h s 1 c m, Тдво-rt e m p e r a t - b r e of t h e g r o u n d a t t h e d e p t h s 50cm Л 1 - g r o u n d - t h a w i n g, T r - g r o u n d thawing r a t e At - d e p t h s of g r o u n d t h a w i n g a r e g i v e n fot" t h e '. l a s t d a y of p e n t a d s Table 2. Correlation coefficients between chosen meteorological conditions and ground thawing rate as well as between ground temperature and ground thawing rate in Kaffioyra (NW Spitsbergen) in the periods since and , Э Del ау ~" С i n day) С U ' О О. 2 2 О. 3 6 О О. 0 О О. Об О. 2 7 О О О О. 3 9 О О о О. 3 о. 5 О. ю О О О О р о о О о. 17 -О о О. Об Ti Tgi Tgso С и Тр C-c.i oud:i n e s s > t ' - s u n s h i n e d u r a t i o n, ' u -a.i r t e m p e r a t u r e, t. emper t. чг e t h e d e p t h Icny. Tg^o g r o u n d t e m p e r a t u r e a t 50cm. Tgi Tgso О. 0 2 igi g r o u n d t h e deot h 273

8 Fig. 1. The course of the chosen meteorological elements and thermoisoplethes of the ground and ground thawing and thawing rate of the ground in Kaffioyra (NW Spitsbergen) in the period since ,1985. С cloudiness, U sunshine duration, Ti air temperature, P precipitation, Tg thermoisoplethes, A1 ground thawing, Tr ground thawing rate 27

9 Sunshine duration Cloudiness С (0-10) Юг i 2 om/d,y a Thawing rate Air temperature Ground temperature с em/<tay Thawing rate o' -1 ' о ' t 1 o m / d a y2 1 ' a Thawing rate Fig. 2. Relationship between of the chosen meteorological elements and ground thawing rate as well as between ground temperature at the depth 1 cm and ground thawing rate in the Kaffioyra (NW Spitsbergen) in the period since ,