Recent ground ice and its formation on evidence of isotopic analysis

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1 Permafrost, Phillips, Springman & Arenson (eds) 2003 Swets & Zeitlinger, Lisse, ISBN Recent ground ice and its formation on evidence of isotopic analysis A.Yu. Dereviagin & A.B. Chizhov Moscow State University, Faculty of Geology, Russia H. Meyer, H.-W. Hubberten & Ch. Siegert Alfred Wegener Institute for Polar and Marine Research, Germany ABSTRACT: Since 1994, the isotopic composition (d 18 O, dd, 3 H) of both relic and recent ground ice and natural waters was studied in detail on Taymyr Peninsula, in the Lena Delta region and on New Siberian Islands in the framework of Russian German research projects. The paper focuses on processes of modern polygonal wedge ice and texture ice formation and examines new data on isotopic composition. More than 400 isotopic composition determinations are discussed in the paper. The modern age ( 50 years) of ground ice is controlled by the tritium content (bomb and technogenic tritium). High tritium concentrations ( 15 TU) in heads and in modern growths of ice wedges as well as in texture ice in the upper part of the permafrost point to intensive processes of modern ice formation. The results of stable isotope analysis show that ground ices and natural waters are fed by meteoric water (snowmelt, rain and its mixtures). Texture ices are fed by mixture of rainwater and snowmelt. Modern wedge ice is mainly formed from snowmelt. However, in some cases the isotopic composition (d 18 O, dd and d-excess) of modern growths of ice wedges and modern snow may differ considerably. The variation of d-excess values between snow and modern ice wedges may amount as much as 6 (New Siberian Islands). The observed variability can result from both processes of mixture of snowmelt and rain-water and of the isotopic composition change due to processes of evaporation/sublimation of initial meteoric water. The stable isotopic composition of modern ground ices is heavier than of the Holocene and the Late Pleistocene ground ices. Differences of isotopic composition between modern and relic ground ices reflect climate changes. 1 INTRODUCTION In the modern view the stable isotope composition of ground ice is considered as unique archive of paleoclimatic information and it correlates well with the mean annual air temperatures (Mackay, 1983, Vaikmäe, 1989, Vasil chuk, 1991, Nikolaev & Mikhalev, 1995, Meyer et al., 2002). The starting point of the paleoclimatic reconstruction is the study of modern climatic conditions, recent ground ice formation processes, isotopic composition of recent ground ices and natural waters and its relationship. Ground ice studies were carried out in the frame of joint Russian German multidisciplinary research projects Taymyr and Paleoclimate signals in ice-rich permafrost in the Laptev Sea region in The isotopic composition (d 18 O, dd, 3 H) of both ground ices (texture ices and ice wedges) and natural waters (rainwater, snow patches, suprapermafrost ground water, surface water) was studied in detail. The main purpose of this paper is to present and to discuss new data on the isotopic composition of ground ice and its relationship to the isotopic composition of modern natural waters in the region. (Taymyr Lake) in 1996, site 3 Bykovsky Peninsula in 1998 and site 4 Bol shoy Lyakhovsky Island in All sites locate at the typical tundra and Arctic tundra zones. The nearest long-term weather stations site in Khatanga, Taymyr Lake, Tiksi and at the Shalaurova polar station respectively. Continental Arctic climate with long, severe winters and short summers is typical for the region (Table 1). Snow cover is formed in September and melts in June. Some of snow patches are conserved during the summer. The thickness of snow cover varies from 0,3 to 0,55 m (sites 1,2,3) and from 0,1 to 0,15 m (site 4). Part of snow is removed by wind in dependence on geomorphologic and landscape conditions. About of 2 STUDY SITES Investigations were conducted at four sites (Fig. 1): site 1 Labaz Lake in 1994/95, site 2 Cape Sabler 193 Figure 1. Location map.

2 Table % of snow cover is evaporated in spring period (Golubev et al., 2001). The study sites belong to the zone of continuous permafrost, reaching m depth. The mean annual ground temperature is about C. The thickness of the active layer varies from 0.2 m on peatlands to m in sandy sediments without vegetation cover. Silt, sandy-silt and peat sediments predominantly present the upper part of the permafrost. The most abundant types of ground ice are texture ice and ice wedges. One of the main geological and cryolithological features of the region is the Ice Complex: very ice rich Late Pleistocene sediments with huge (of about m thickness) syngenetic polygonal ice wedges. According to 14 C dates of enclosing sediments (Dereviagin et al., 1999, Siegert et al., 1999, Schirrmeister et al., 2002) and data on tritium analysis (Chizhov et al., 2001), ground ice formation in the region took place widely during the Late Pleistocene, the Holocene and still occurs at present time. Both the Late Pleistocene and the Holocene ground ices are the subjects of paleoclimatic investigations. 2 METHODS Climatic conditions of study sites. Mean air temperature ( C) Precipitation (mm) Site Year Winter Summer Year Winter 1. 13,0 22,5 8, ,0 22,2 4, ,2 21,9 5, ,7 21,6 1, The investigations are based on the combined application of both tritium ( 3 H) and stable isotope ( 18 O, D) analyses. Tritium ( 3 H) is a radioactive hydrogen isotope with a decay constant of 12.4 years. Modern water with tritium is produced and precipitated out of the atmosphere since 1952, when the first hydrogen bomb was exploded. The tritium concentration having regard to radioactive decay can be calculated by use of the following equation (Ferronsky et al., 1984): C t C 0 exp( lt); (1) (Where: t age, l 0,056 constant of the radioactive decay, C 0 tritium concentration in precipitation t years ago). Tritium is a component of the water molecule (as hydrogen and deuterium), traces the modern water (younger than 1952) content in permafrost and can be used as an indicator of modern ground ice formation processes (Michel & Fritz, 1978, Chizhov & Dereviagin, 1988, Burn, 1990). An elevated tritium concentration in ground ices points to its growth during the last 50 years. The application of stable isotope method for the study of ground ice is based on the comparison of the isotope composition (d 18 O, dd) and the d-excess of ice and of recent winter precipitation. The deuterium excess d: d dd 8d 18 O; (2) was defined in order to relate the isotope composition of any water sample to the global meteoric water line (GMWL) and to identify non-equilibrium processes (Dansgaard, 1964). Modern texture ice (segregated ice and ice cement) situated in the upper part (2 4 m) of permafrost in the modern and the Holocene sediments was sampled both in boreholes and in outcrops. The sampled modern growths of ice wedges were situated in frost cracks in the lower part of active layer and in the transition layer. Modern growths penetrate into upper parts ( heads ) of relic (usually the Holocene) ice wedges. Samples of ice and snow were collected using a special ice screw (1.5 cm in diameter) and then were thawed out in the field laboratory. Melt-water and natural waters were collected directly into plastic flasks. In more detail the sampling strategy is described in Dereviagin et al., 1997, Meyer et al., Laboratory measurements of isotope ratios (d 18 O, dd) were carried out at the Alfred Wegener Institute of Polar and Marine Research in Potsdam (Germany), using a Finnigan MAT Delta-S mass spectrometer. The stable isotopic composition is presented in vs. V-SMOW standard. The internal error is about 0.1 for d 18 O and about 0.8 for dd. Tritium concentration was evaluated at the Moscow State University (Russia), using a liquid-scintillation spectrometer Tricarb-1600 with an instrumental error of about 10%. The detection limit of tritium concentration is 15 TU. 3 RESULTS AND DISCUSSIONS 3.1 Isotopic composition of natural waters Since 1952 mean annual tritium concentrations in precipitation are controlled by hydrogen bomb tests. The bomb tritium peak is observed in 1963 (about of 4000 TU). Now, much lower tritium concentrations of TU are measured. Usually tritium concentrations in rain are half again than in snow. However, elevated tritium concentrations 194

3 we observed in some of snow patches in the region (Chizhov et al., 2001). At the Taymyr region in 1994/96 (site 1 and 2) tritium content in several snow patches reached of about 420 TU. At site 3 (winter 1997/98) the mean value of tritium concentration in snow patches was about of 150 TU (maximum of 207 TU), while in rain of no more than 42 TU. Mean value of tritium concentration of snow samples at site 4 (winter 1998/99) is about 55 TU, the maximum value is 98 TU. At all sites some of snow patch samples have low tritium concentration from about of 15 to 21 TU. This data shows the uneven character of tritium arrival to atmospheric precipitation in winter period. Such an intensive tritium arrival to winter precipitation bears most likely local and episodic character. But high tritium content found in modern snow can be used as a regional snowmelt mark. The tritium content in surface water and in suprapermafrost ground water at sites 1 and 2 is not more than TU and reaches about 150 TU at sites 3 and 4 (close to tritium concentration in snow). Elevated tritium concentrations in surface water are typical for small ponds fed by snowmelt water. Mean annual values of d 18 O in atmospheric precipitation in the region estimate to be about 22 to 24 (Brezgunov et al., 1998). Data on the mean regional values of the isotopic composition (d 18 O, dd, d-excess) of natural waters and ground ices is presented in the d 18 O-dD diagram (Fig. 2) and in Tables 2, 3, and 4. The combination of annually precipitated meteoric water (snow and rain) forms surface and suprapermafrost ground waters and different types of ground ices. The first approximation of their isotopic δ O -100 Sn IW (Ho) TI (P) GMWL GW TI (Mo) IW (Mo) SW R δd Figure 2. Mean isotopic composition of ground ices and natural waters in Laptev Sea region. Legend: Sn snow patches; R rainwater; IW (Ho) Holocene ice wedges; IW (Mo) modern growths of ice wedges; TI modern texture ice; TI (P) Late Pleistocene texture ice; GW suprapermafrost ground water; SW surface water; GMWL Global Meteoric Water Line. Table 2. Mean isotopic composition of snow patches, rainwater and surface water. Site n* d 18 O dd d-excess Snow patches ,5 181,0 11, ,8 191,3 16, ,4 185,5 10, ,9 204,3 11,2 Mean value 25,4 190,5 12,2 Rainwater ,3 140,1 3, ** 16,2 127,2 2, ,8 115,7 2, ,0 101,1 4,4 Mean value 15,1 121,0 1,0 Surface water ,6 138,2 2, ,9 150,7 8, ,0 130,3 5, ,8 131,5 4,9 Mean value 17,0 134,3 1,5 * Number of samples; ** Data of J. Boike (1997). Table 3. Mean isotopic composition of suprapermafrost ground water and of texture ice. Site n d 18 O dd d-excess Suprapermafrost ground water ,2 140,7 12, ,5 144,4 11, ,8 130,7 3,4 Mean value 18,3 137,9 8,1 Texture ice ,9 146,4 12, ,0 138,5 5, ,4 152,3 11, ,9 145,0 5,8 Mean value 19,3 145,6 8,7 Table 4. Mean isotopic composition of modern growths of ice wedges and Holocene ice wedges. Site n d 18 O dd d-excess Modern growths ,8 143,6 14, ,4 155,4 7, ,1 180,3 12, ,0 162,6 4,8 Mean value 21,3 160,5 9,8 Holocene ice wedges ,8 179,4 10, ,1 171,4 13, ,2 210,8 14, ,9 184,0 7,1 Mean value 26,2 197,7 11,5 195

4 δ 18 O -30 δ 18 O Sn -25 Sn R SW GW Proportion of snowmelt % IW(Mo) R TI (Mo) Proportion of snowmelt % Figure 3. Mean regional values of snowmelt proportion in surface water (SW) and suprapermafrost ground water (GW). Solid line mean regional value, dotted lines variations, Sn snow patches, R rainwater. Figure 4. Mean regional values of snowmelt proportion in modern texture ice (TI (Mo)) and in recent growths of ice wedges (IW (Mo)). Solid line mean regional value, dotted lines variations, Sn snow patches, R rainwater. composition can result from the mixture of rainwater and snowmelt. Figure 3 demonstrates a rough measure of proportions of snowmelt in investigated natural waters and ground ices. The influence of isotopic composition of snowmelt is the least pronounced in surface water (mean value is about of 17%, variations are from 7 to 45%) (Fig. 3). The percentage of snowmelt in suprapermafrost ground water in July August varies from 15 to 45% (mean value of about 32%). The isotopic composition of suprapermafrost ground water essentially depends on landscape conditions, which control the distribution of snow cover. For example, at site 4 in different landscapes values of d 18 O vary from 13,8 to 19,2, and d-excess values from 5,2 to 10, Isotopic composition of texture ice Data on tritium analysis shows the availability of modern water (younger than 1952) in texture ice to a depth of about 3 4 m in the region. Mean values of tritium concentrations in texture ices vary from 35 TU at site 1 to 220 TU at site 3. The stable isotope composition (d 18 O, dd) and the d-excess of texture ice and of suprapermafrost ground water are presented in Table 3. The percentage of snowmelt in texture ice can vary from 35 to 65%, mean value is about of 45% (Fig. 4). Mean isotopic composition of texture ice is very close to suprapermafrost ground water (the differences in d 18 O values are not more than 2 (Table 3)). This demonstrates that the suprapermafrost ground water is the main source of forming texture ice in the upper part of permafrost. More negative values of d 18 O of texture ice at site 3 point to more intensive snowmelt feed. This is supported by tritium analysis data: high tritium concentration in 90% of samples is observed. While, the isotopic composition of texture ice is subject to wide variation even within one site (to 4 6 for the d 18 O, and to 10 for d-excess). This is because of differences of landscape conditions and lithology (peat inclusion) and possible influence of isotopic fractionation. The mean oxygen isotopic composition of texture ice in the Holocene deposits is of about 3 heavier than in the Late Pleistocene deposits. These variations seem to be associated with climate changes during the Late Pleistocene and the Holocene. 3.3 Isotopic composition of modern ice wedges The tritium concentration in modern ice wedges at site 1 reaches 80 TU. Furthermore the tritium concentrations (of about TU) were determined in modern growths and heads of ice wedges at sites 3 and 4. The measured concentrations are very close to tritium concentrations in snow. High tritium concentrations found in modern growths of ice wedges at sites 1, 3 and 4 demonstrate its intensive growth and snowmelt feed. Low tritium content (from less than 15 TU to of TU) in modern growths and in heads of ice wedges found at site 2 points to inactive character of modern ice wedge formation during last 50 years. The obtained data is in a good agreement with data on tritium analysis of modern ice wedges in the North of Canada. At site Mayo, Yukon Territory tritium concentrations vary from 44 TU to 274 TU (Burn, 1990) 196

5 and at Ellesmere Island from less than 6 TU to 123 TU (Lewkowicz, 1994). The stable isotope composition (d 18 O, dd) and the d-excess of modern growths of ice wedges and Holocene ice wedges are presented in Table 4. Mean values of isotopic composition of modern growths of ice wedges and Holocene ice wedges lie close to the GMWL (Fig. 2) and are located between snowmelt and suprapermafrost ground water. The percentage of snowmelt in ice wedges growths varies from 45 to 90% (mean value is of about 70%) (Fig. 4). The isotopic composition closest to snowmelt was found in growths of ice wedges at site 3 (90% of snowmelt). The isotopic composition of ice wedge growths at sites 2 and 4 is characterized by high proportion (30 40%) of water enriched in heavy isotopes (rainwater, surface water, suprapermafrost water). This is supported by the facts that d-excess values of ice wedge growths (Table 4) at these sites are very low (7,8 and 4,5 respectively). While the observed discrepancy between the isotopic composition of ice wedge and snow and the gap in d-excess can possibly result from processes of snow and ice isotopic composition modification. The processes of evaporation and sublimation both in snow cover and in open frost cracks can be responsible for this modification and are under discussions (Golubev et al., 2001, Taylor et al., 2001, Dereviagin et al., 2002). The stable isotopic composition of modern growths of ice wedges is predominantly fed by winter precipitation and reflects well mean winter temperature conditions. The pronounced differences in isotopic com position of Late Pleistocene, Holocene and modern ice wedges demonstrate changes of winter climatic conditions in the Laptev Sea region (Meyer et al., 2002). 4 CONCLUSIONS On evidence of isotopic analyses investigated types of ground ices and natural waters are fed by meteoric water. Differences in the isotopic composition and the d-excess of snowmelt and rainwater can be used for the estimation of their involvement in the ground ice formation. Results on tritium analyses point to intensive processes both of texture ice formation and modern ice wedge formation in the upper part (2 4 m) of permafrost. The proportion of enriched in heavy isotopes rainwater and isotopically light snowmelt substantially determines the isotopic composition (d 18 O, dd) of forming ground ice. Modern texture ice is predominantly fed by suprapermafrost ground water and includes both snowmelt and rainwater, which content is mainly controlled by landscape conditions. The mean percentage of rainwater in texture ices is about of 60%. Differences of the isotopic composition between texture ices in the Holocene and in the Late Pleistocene deposits can be associated with climate changes. Isotopic composition of modern growths of ice wedges is predominantly fed by snowmelt and reflects well mean winter temperature conditions. The percentage of snowmelt in growths of ice wedges varies from 45 to 90%. The considerable enrichment in heavy isotopes in comparison to snowmelt and the gap in d-excess characterize the isotopic composition of recent ice wedges at sites 2 and 4. This can result from both mixture of snowmelt and rainwater and processes of snow and ice isotopic composition modification. REFERENCES Brezgunov, B.S., Yesikov, A.D., Ferronsky, V.I. & Sal nova, L.V Spatial-temporal variations of oxygen isotope composition in precipitation and river water of Northern Eurasia and their relation to temperature changes. Water Resources 25(1): (In Russian). Boike, J Thermal, hydrological and geochemical dynamics of the active layer at continuous permafrost site Taymyr Peninsula, Siberia. Reports on Polar Research 242: 104. Burn, C.R Implications for paleoenvironmental reconstruction of recent ice wedge development at Mayo, Yukon Territory. Permafrost and Periglacial Processes 1: Chizhov, A.B. & Dereviagin, A.Yu Tritium in Siberia s Permafrost. In Lewkovicz, A.G. & Allard, M. (Eds), Proceedings, Seventh International Conference on Permafrost, Yellowknife, June 23 27, Nordicana 57, Quebec City, University Laval: Chizhov, A.B., Dereviagin, A.Yu. & Simonov, E.F New data on tritium analysis of ground ices and natural waters of Eastern part of Russian Arctic. Proceedings of II Conference of geocryologists of Russia, Moscow 6 8 of June 2001: Dansgaard, W Stable isotopes in precipitation. Tellus 16: Dereviagin, A., Siegert, C., Troshin, E. & Simonov, E. (1997). Permafrost Landscapes and Geocryology of Cape Sabler. 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6 a seasonal snow cover on formation of an isotopic content of wedge ice. Cryosphere of Earth 5(3): (In Russian). Lewkowicz, A.G Ice-Wedge rejuvenation, Fosheim Peninsula, Ellesmere Island, Canada. Permafrost and Periglacial Processes 5: Mackay, J.R Oxygen isotope variations in permafrost, Tuktoyaktuk Peninsula Area, Northwest Territories. Current Research, Part B, Geological. Survey of Canada, Paper 83 1B: Meyer, H., Dereviagin, A. & Syromyatnicov, I. (1999). Ground Ice Studies: Paleoclimatic Signals of Ice-rich Permafrost. In Russian German Co-operation: System Laptev Sea 2000: In V. Rachold (Ed.), The Lena Delta 1998 Expedition, Reports on Polar Research, 315: Meyer, H., Dereviagin, A.Yu., Siegert, Ch. & Hubberten, H.-W. (2002). Paleoclimatic studies on Bykovsky Peninsula, North Siberia Hydrogen and oxygen isotopes in ground ice. Polarforschung 70: Michel, F.A. & Fritz., P Environmental isotopes in permafrost related waters along the Makenzie valley cor-ridor. In Proccedings, Third International Conference on Permafrost, Ottawa, Vol. 1: Nikolaev, V.I. & Mikhalev, D.V An oxygen-isotope paleo-thermometer from ice in Siberia permafrost. Quaternary Research 43(1): Schirrmeister, L., Siegert, Ch., Kunitsky, V.V., Sher, A., Grootes, P. & Erlenkeuser, H Late Quarternary ice-rich permafrost sequences as an archive for the Laptev Sea Region paleoenvironment. International Journal of Earth Science 91: Siegert, C., Dereviagin, A.Y., Shilova, G.N., Hermichen, W.-D. & Hiller, A Paleoclimatic Indicators from Permafrost Sequences in the Eastern Taymyr Lowland: In H. Kassens, H.A. Bauch et al., (Eds) Land-Ocean Systems in the Siberian Arctic, Dynamics and History. Springer-Verlag Berlin Heidelberg: Taylor, S., Feng, X., Kirchner, J.W., Osterhuber, R., Klaue, B. & Renshaw, C.E Isotopic evolution of a seasonal snowpack and its melt. Water Resources Research 37(3): Vaikmäe, R Oxygen isotopes in permafrost and ground ice a new tool for paleoclimatic investigations. 5th Working Meeting Isotopes in Nature, Proceedings, Leipzig, September 1989: Vasil chuk, Yu.K Reconstruction of the paleoclimate of the Late Pleistocene and Holocene on the basis of isotope studies of subsurface ice and waters of the permafrost zone. Water Resources 17(6):

REGIONAL PROBLEMS OF EARTH S CRYOLOGY COMPARATIVE ANALYSIS OF THE ISOTOPIC COMPOSITION OF ICE WEDGES AND TEXTURE ICES AT THE LAPTEV SEA COAST

SCIENTIFIC JOURNAL EARTH S CRYOSPHERE Kriosfera Zemli, 2016, vol. XX, No. 2, pp. 14 22 http://www.izdatgeo.ru REGIONAL PROBLEMS OF EARTH S CRYOLOGY COMPARATIVE ANALYSIS OF THE ISOTOPIC COMPOSITION OF ICE