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International Journal of EnvironmentalStudiesPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/genv20
Permafrost thawing inferred fromArctic lake sediment of the TaimyrPeninsula, East Siberia, RussiaA.P. Fedotov a , M.A. Phedorin b , A.S. Suvorov a , M.S. Melgunov c
& T.V. Khodzher aa Limnological Institute of the Siberian Branch of RAS , Ulan-Batorskaya st., 3, Irkutsk , 664033 , Russiab Institute of Petroleum Geology of the Siberian Branch of RAS ,Academician Koptug av., 3, Novosibirsk , 630090 , Russiac Institute of Geology and Mineralogy of the Siberian Branch ofRAS , Academician Koptug av., 3, Novosibirsk , 630090 , RussiaPublished online: 21 Feb 2012.
To cite this article: A.P. Fedotov , M.A. Phedorin , A.S. Suvorov , M.S. Melgunov & T.V.Khodzher (2012) Permafrost thawing inferred from Arctic lake sediment of the TaimyrPeninsula, East Siberia, Russia, International Journal of Environmental Studies, 69:1, 7-19, DOI:10.1080/00207233.2012.619879
To link to this article: http://dx.doi.org/10.1080/00207233.2012.619879
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Permafrost thawing inferred from Arctic lakesediment of the Taimyr Peninsula, East Siberia,
Russia
A.P. FEDOTOV*y, M.A. PHEDORINz, A.S. SUVOROVy, M.S. MELGUNOVxANDT.V. KHODZHERy
yLimnological Institute of the Siberian Branch of RAS, Ulan-Batorskaya st., 3, Irkutsk 664033,Russia; zInstitute of Petroleum Geology of the Siberian Branch of RAS, Academician Koptug av., 3,Novosibirsk 630090, Russia; xInstitute of Geology and Mineralogy of the Siberian Branch of RAS,
Academician Koptug av., 3, Novosibirsk 630090, Russia
(Received 31 August 2010)
The objective of this paper is to reconstruct permafrost thawing at 71�N of Arctic Siberia duringthe termination of the Little Ice Age and the subsequent Recent Warming. Sediment samples fromLake Dalgan of the Taimyr Peninsula were analysed by high-resolution X-ray fluorescence spec-troscopy at 1 mm scan resolution, and Fourier-transform infrared techniques. Intense permafrostthawing was calculated from the level of terrigenous and leached matter supplied by meltwaterinto the lakes. We defined three episodes of increased permafrost thawing during the last 170years. The first maximum of permafrost melting occurred from 1870 to 1880, the second episodewas from 1900 to 1930 and the third began from 1960 and continues to date. During theseperiods, maxima of permafrost melting occurred with a specific time lag following temperaturemaxima.
Keywords: Arctic Russia; Permafrost thawing; XRF-SR scan; FTIR
1. Introduction
It is well-recognised that the high northern latitudes are highly sensitive to global climateand other environmental changes [1–3]. Some polar regions have even exhibited awarming of as much as 2�C per decade [4]. Nevertheless, the climate pattern of the highaltitudes is not uniform when the atmosphere responds to positive oceanic temperatureanomalies with a modified circulation that leads to increased heat outflow across 70�Ntowards Siberia and to reduced heat inflow over Alaska and Canada [5,6]. Hence, it shouldnot be expected that the paleo-records of different regions exactly match due to the dipolartemperature response of regions.
Permafrost, a major element of the global cryosphere, is particularly sensitive to climatechange. The total occurrence area of continental permafrost in the Northern Hemisphere isnow �26 million km2 [7]. The threat of global warming and its effects upon the
*Corresponding author. Email: [email protected]
International Journal of Environmental Studies,Vol. 69, No. 1, February 2012, 7–19
International Journal of Environmental StudiesISSN 0020-7233 print: ISSN 1029-0400 online � 2012 Taylor & Francis
http://www.tandf.co.uk/journalshttp://dx.doi.org/10.1080/00207233.2012.619879
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permafrost of the world have been widely discussed in the scientific community [8–11].The permafrost zones contain large amounts of organic carbon and act as carbon sinks,and a temperature increase will result in a release of carbon into the atmosphere.
The main characteristics of the permafrost zone are its occurrence area and depth andthe temperature, and depth of the active layer. The surface 0–45 cm of the soil generallythaws during the summer months; below this depth, the soil remains frozen throughout theyear [12]. Analysis has shown statistically significant increase in the thickness of the activelayer of permafrost in the recent 35 years in different regions of the permafrost zone of theNorthern Hemisphere, averaging �1 cm per year [13,14]. Time series data from the north-ernmost boreholes suggest rapid recent warming of the permafrost, rates at the permafrosttable being estimated as �0.06�C per year in Western Siberia, 0.05�C per year in arcticCanada and 0.04–0.07�C per year in Svalbard and Scandinavia [15–17].
The goals of the present paper are to reconstruct a response of permafrost to climatechanges based on high-resolution geochemical proxies inferred from Arctic lake sediment(the Taimyr Peninsula, arctic Russia) during the last 170 years. Records of this period bearcritical information about significant climate changes, for example, the transition from theLittle Ice Age (LIA) to the Recent Warming (RW) and the beginning of anthropogenicallyforced global warming.
2. Regional setting of study area
This study was conducted near the Sopkarga Cape of the Yenisei River in western part ofthe Taimyr Peninsula. Benthic core were collected from Lake Dalgan in early September of2009 (figure 1). Lake Dalgan (71,908�N, 82,690�E) is about 3 km2 and the water depthwas 6 m at the core-sampling site. The climate in the Taimyr region is continental, reflectedin the large differences in the mean January (-28 to -36�C) and mean July (8–12�C) temper-atures. Annual precipitation is relatively low, ranging from 200 to 400 mm, with the precip-itation largely accumulating during the winter as snow, which melts rapidly in early June[18]. The vegetation around the studied lakes presented grass-moss cover and scatteredshrubs (Erycales and dwarfish willows). Green mosses (Polytrichum, Tuidium, Dicranumand Aulacomium) prevailed, while sphagnum mosses and lichens (Cladonia) did not.Among the grasses, Carex and Gramineae were the main species. Permafrost thickness isabout 400–600 m, and this permafrost is continuous. The average trend of annual groundtemperatures is 0.05�C per year in the study area for the last 50 years [19,20].
3. Methods
Dating of the Dalgan core was based on 210Pb and 137Cs chronology. Measurement of238U, 234Th, 226Ra, 137Cs and 210Pb contents in the studied samples was carried out usinga high-resolution semiconductor gamma-spectrometry technique. Low-energy gamma lineswere used as analytical signals: 46.5 keV for 210Pb, 63.3 and 92 keV for 238U (by 234Th)and 186.1 keV for 226Ra. We calculated a depth-age relationship for the uppermost 7 cmof the Dalgan core using the Constant Rate of Supply (CRS) model [21]. The ConstantInitial Concentration (CIC) method could not be applied because the profile showed a non-exponential form. The average sediment accumulation ratio (ASAR) is the mean valuebetween the models using unsupported 210Pb concentrations calculated by 238U and 226Ra.
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Figure 1. Location of Lakes Dalgan; circle – position of the analysed core; triangle – altitude above sea level.Upper panel – location of objects shown in figure 6; 1 – Lakes Dalgan; 2 – Lake Taimyr.
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X-ray fluorescence spectroscopy was undertaken to provide quantitative information on20 trace elements (from K to U) under a 1 mm monochromatic synchrotron beam (XRF-SR scan) using an instrument previously described by Zolotarev et al. [22] and employinga method for measurement quantification reported by Phedorin et al. [23].
The content of organic matter and clay was investigated using Fourier-transform infrared(FTIR) spectroscopy. FTIR spectra were recorded on an FSM-101 FTIR Spectrometer(Infraspect�) as KBr pellets (3 mg sample/170 mg KBr) at wave numbers from 700 to4000 cm-1. Twenty-four scans were averaged with a resolution of 1 cm-1 by subtractingvalues obtained from pure KBr pellets. We used an absorbance band around 1740–1500cm-1 to calculate the ratio of organic matter in lake sediments This absorption range com-bined several overlapping functional groups of organic compounds. The main peak for allspectra occurred around 1630 cm-1, and this was attributed to aromatic (C=C) or amide I(O=C-N) groups. Broad and moderate bands around 1540 cm-1 indicated the presence ofnitrogen-containing groups (C-N, N-H and N=O) [24,25]. A broad band around 1680–1710 cm-1 is typical for carboxyl groups (C-O or C=O).
Statistical analyses were performed using factor analysis where factors were initiallyextracted using principal components analysis and then redistributed using the varimaxrotation method.
Water content (WC) was determined by weighing wet sediment and the residue afterdrying at 60�C, and the sampling resolution was 1 cm. The pH along cores was measuredby testo 206-pH2 of testo�.
4. Results
The core from Lake Dalgan was 39 cm in length and consisted of two types of sediment.The bottom of the core (30–39 cm) presented fine, bluish clay. The average WC was25–35% and the pH was 6.3–6.4 (figure 2). We assumed that this interval was most likelynot formed by lake conditions, consisting mainly of redeposit sea-clay. The upper part(0–30 cm) of the core was formed by silty clay enriched with gittja layers or lens. Thegittja layers contained coarse, well-preserved remains of aquatic and ground plants in siltyclay. The WC varied widely from 30 to 70% and the pH was about 6.3 (figure 2). The topof the core (0–3.5 cm) was the oxidised layer. Based on these lithologic features weassumed the interval from 0 to 30 cm was formed under lake conditions.
The calculated ASAR in this study was 0.18 cm yr-1 for the Dalgan core. However, the137Cs dates did not show the two typical peaks for the fallout from nuclear weapon testing(AD 1963) and from the Chernobyl incident (AD 1986). We therefore assumed that sedi-ments had low values (2–5 Bq kg-1) of 137Cs formed until 1949, as this was the beginningof nuclear weapons testing (figure 3). If this assumption was correct, the sediment accumu-lation ratios (SAR) calculated by 137Cs were 0.12 cm yr-1. The SAR dates very well withASAR dates. Based on lithologic features and geochemical composition (see below) of thecores, we extrapolated the ASAR date down to 30 cm for the Dalgan.
Measured FTIR spectres of lake bottom sediments consisted of three main spectra:i) autochthonous lake matter; ii) components washed out from soil and soil detritus; andiii) redeposited organic matter from sea clay. The result of principal component analysisshowed that spectres of organic matter from different part of the core were not uniform(figure 4). Spectres of bluish clay were characterised as being a poor set of functionalgroups of organic compounds (e.g. alkyls, carbonyls, amide II and I and nitrates).
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Beginning at 30 cm and moving upward, the content of organic groups graduallyincreased. In this region, amide I or carbonyl (C=C) groups were the dominantcomponents of the determined organic components. Specifically, a high content of nitro-gen-containing groups occurred close to the bottom boundary of the gittja layers, andcarboxyl groups occurred for typical autochthonous lake sediments. Total organic contentamounts were 5–6% for bluish clay, and 4–12% for lake sediments (figure 4).
Using factor analysis with the criterion of an eigenvalue of 1, three main factors weresuccessfully extracted from 20 variables of the core (figure 5, table 1).
Factor 1 (F1), which accounted for 52% of the total variation, had a large factor loadingfor K, Ca, Ti, Cr, Mn, Fe, Ni, and Zn. The elements K and Ca are common constituents ofprimary minerals and they all can form soluble compounds. Consequently, these elementscan be used to reflect the intensity of weathering and leaching in the watershed. The mobil-ity of Fe and Mn is known to be redox driven and so it can be used to reflect general condi-tions for soil development in the watershed [26]. Cr, Ni, and Ti strongly associated withcolloidal iron [27]. In general, this factor can describe intensity of weathering, leaching anddevelopment of soils in the watersheds.
Figure 2. Lithological composition, water content (WC) and pH of the Dalgan core.
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Factor 2 (F2), which accounted for 15% of the total variation, had a large factor loadingfor Cu, Ga, Y, Br, Th and U. Direct XRF measurements of modern organic rain from bottomsediments revealed active accumulation of Br by living organisms in Siberian and Mongo-lian lakes [28]. In addition, it is well known that U and Cu easily incorporate into organicmaterials. Therefore, Cu, Br and U in lake sediments can be regarded as autochthonous inorigin. Th is a very stable insoluble oxide and is primarily transported as suspended particu-lates, so the effects of weathering and diagenesis are very minor [29]. Experimental datahave revealed that the ratio of leached Th directly depended on the drainage activity of thesoil [30]. We assumed that the high ratio of Th in lake sediments was caused by high-inten-sity leaching of Th from the soil by surface water when the permafrost thawing rate washigh. A close conformity between the profiles of Th and the instrumental measurements ofthe changes of the level of Lake Taimyr [31] confirmed our premise (figure 6).
Factor 3 (F3), which accounted for 13% of the total variation, had a large factor loadingfor Zr, Sr, Nb and Mo. Mo is fixed with organic matter and secondary iron and manganeseoxides which have flocculated and precipitated onto clay-size aluminosilicates [32]. Per-haps Mo was remobilised from bluish clay occurring in the watershed by surface water. Zrand Nb strongly associated with large size colloidal iron and aluminium were supplied bysurface water [27].
The bottom part was characterised by low Sr/Rb and Ca/Ti ratios and high Fe/Mn andFe/Ti ratios (figure 5). In addition, the content of practically all analysed elements was lowin the bottom part (39–30 cm) of the core. This is evidence that these sediments wereintensively leached and very likely are redeposited. In addition, low contents of autochtho-nous elements of Factor 2 confirmed the premise that these are not sediments from thelake of origin. Probably, the bottommost levels of this core consist of redeposit Late Pleis-tocene material of marine genesis. This marine bluish-grey clay broadly occurs in this partof the Taimyr Peninsula [33]. Conversely, the content of elements increased in the 26–0cm interval of the core. The maximum content of elements localised around the lithologic
Figure 3. The depth-age model of the cores based on radioactive isotopes 210Pb, 238U, 226Ra and 137Cs. ASAR –average sediment accumulation ratio to mean values between models using the unsupported 210Pb concentrationcalculated through 238U and 226Ra. SAR – sediment accumulation ratio calculated though 137Cs.
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boundaries of 24 cm (gittja layer) and 4 cm (oxidised/reduced boundary) (figure 5). Inter-estingly, the distribution of Br was different from the other elements. A high content of Brwas in the 26–22 cm interval. Element compositions of the upper parts of the core indicatethat accumulation of sediments prevailed over its redeposit. The increased content of ele-ments Factor 2 and total content of organic matter show that the proportion of autochtho-nous sediments has risen. We assume that the upper parts of these cores were most likelyformed under lake conditions.
5. Discussion
Periods of global warming were a key factor that initiated thermokarst activity [11,34].According to many reconstructions of global surface temperatures for the NorthernHemisphere, a transition from the LIA to the recent warming period was characterised bya sharp increase in annual temperature that occurred at c. 1850–1860 [33–37]. Lithologicalcharacteristics, organic contents and elements composition of the core suggest that there
Figure 4. FTIR spectra for organic matter of the Dalgan core. A – result of the principal component analysisshowed distribution of different organic matter along the core; B – examples of organic functional groups fromdifferent parts of the core. C – PCA-1, 2, and 3 were the explained variances of principal component 1, 2 and 3,respectively, Corg – total content of organic matter, grey rectangles – interval of bluish clay.
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are two distinct types of sediments. The results of dating showed that the lake sedimentsbegan to form at c. 1840. We assumed that the climate regime of the LIA probably endedin the Taimyr Peninsula at this time. Based on our geochemical records we defined threesignificant periods of increased permafrost thawing during the last 170 years.
The first period, 1865 to 1885
Low ratios of Factor 1 variables and Th, and a poor set of organic functional groupsshowed that permafrost thawing was not intense until 1865 in the Taimyr Peninsula. Thereare high concentrations of Factor 1 and 2 variables and total organic matter in the corearound 1870–1880 (figure 6), indicating a higher influx of weathered and eroded materialsinto the lake, and the high watering of the tundra landscape. Moreover, the high values of
Figure 5. Distribution of some elements in the sediments of the Dalgan core. Grey rectangles – showed thesediments formed under lake condition.
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Br in the sediments of Lake Dalgan evidenced its high trophic status at the time. This setof data suggested a large supply of meltwater into the lakes during that period. In addition,the extent of ice in the Nordic Seas was dramatically also reduced from 1870 to 1880 dueto intensive warming of the high northern latitudes [39].
The second period, 1900 to 1930
An increased percentage of total organic matter and a high variety of functional groupsas markers of higher levels of vegetation suggest that climate in the region was notseverely cold during this period. This increasing of permafrost degradation at that periodis unexpected for us, because 1900–1920 was known to have decreasing surface temper-atures in the Northern Hemisphere. A possible explanation for this contradiction may bethat the patterns of regional temperature anomalies of this period did not fully match.For example, the profiles of surface temperature reconstructions for Northern Siberiawere warmer than those of Northern Europe [40]. In addition, summer temperaturesclearly decreased, but spring and autumn temperatures did not [36,41]. According to treering reconstruction, this cold was not deep within the Taimyr Peninsula [40,42].
The third period of permafrost degradation, 1960 to the present
This coincides with the global increase of surface temperature in the Northern Hemisphere[43–45]. It is noteworthy that, since 1950, the Arctic Oscillation has shown a statistically sig-nificant trend towards a positive phase [46], which is thought to indicate global climatechange. The regional trend towards an increase of the mean annual air temperature for thelast three decades was between 0.01 and 0.06�C per year [20,47]. Maximal concentrations ofFactor 1 and 2 variables in the upper part of the core indicate that the response of permafrost
Table 1. Result of the factor analysis
Variables
Factors
1 2 3
K 0.94 �0.12 0.24Ca 0.87 �0.04 0.38Ti 0.90 0.04 0.38Cr 0.77 0.24 0.26Mn 0.89 0.07 �0.01Fe 0.89 0.20 �0.07Ni 0.82 0.39 0.11Cu 0.57 0.74 0.16Zn 0.79 0.51 0.22Ga 0.49 0.62 0.49Br �0.24 0.93 0.02Rb 0.60 0.43 0.48Sr 0.49 0.38 0.74Y 0.29 0.63 0.67Zr 0.28 0.07 0.89Nb 0.26 0.45 0.74Mo �0.14 0.04 0.84Pb 0.60 0.31 0.06Th 0.18 0.78 0.40U 0.18 0.60 0.51Total variance (%) 57.5 16.7 8.9
Note: factor loading > 0.6 are bold.
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on the warming was the most significant for the last 170 years. According to our data, themost significant permafrost thawing occurred from 1980 to 1990, and this date range closelyagreed with the instrumental data for the changes of the level of Lake Taimyr (figure 6).
Figure 6. Proxy records of supplying of melted water from permafrost in Lake Dalgan in comparison with otherrecords: A – distributions of thorium (circles) in the sediments in comparison with the instrumental measurementsof the changes in level of Lake Taimyr [27] and mean interpolated summer temperatures for study area [49];B – temperature anomalies in the Taimyr Peninsula according to [33], grey rectangles – three periods of increasedpermafrost thawing. F1 (stack) – averaging depth profiles of normalised concentrations of elements of Factor 1.
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It is obvious that there is a direct relation between surface temperatures and intensivethawing of the permafrost. However, the time response of the permafrost upon warmingcan be incompletely synchronous. For example, if our proxies of permafrost thawing andthe instrumental measurements of Lake Taimyr levels are generically compared with theregional temperature profile (figure 6), their maximums did not match. Meltwater maximaoccurred with a certain time lag following temperature maxima. We assumed that perma-frost actively thawed during 1870–1880, which was induced by sharp warming in about1860. Permafrost melting from 1900–1930 was induced by a longer warming period from1880 to 1895 and was also partially due to the one in 1920 (figure 6). According to thereconstruction of Osborn and Briffa [38] for Arctic Siberia, the temperature anomaly thatoccurred around 1930–1950 was the more significant and longer lasting in the TaimyrPeninsula than for the Yamal Peninsula (Western Siberia, see figure 1) or the lower latituderegions of East Siberia [40,48]. It is highly probable that this temperature anomaly and theglobal increase of surface temperature for the last few decades caused an increasing trendof permafrost melting that began about 1960 and continues to date.
6. Conclusions
We reconstructed permafrost dynamic in the Taimyr Peninsula (Arctic Siberia, Russia) forthe last 170 years based on geochemical proxies (X-ray fluorescence spectroscopy at a reso-lution of 1 mm, Fourier-transform infrared spectroscopy) from bottom sediments of LakeDalgan located at 71�N. Intense permafrost thawing was calculated from the level of terrige-nous and leached matter supplied by meltwater into the lakes. The sediment cover of thislake began to form at c. 1840, and we assumed that the recent warming started around thistime. But the maxima of permafrost melting and regional surface temperature did not coin-cide. Additionally, meltwater maxima occurred with a specific time lag following tempera-ture maxima. Permafrost thawing was not intense until 1865, with the first maximum ofpermafrost melting occurring between 1870 and 1880 and one was induced by sharp warm-ing in about 1860. The second permafrost melting episode was around 1900–1930 and onewas induced by a longer warming period from 1880 to 1895 and was also partially due to theone in 1920. The third period of permafrost degradation from 1960 to the present coincideswith the global increase of surface temperature in the Northern Hemisphere
Acknowledgements
We are grateful to Osipov E. Yu, Suslova M. Yu, I.V. Tomberg and A.D. Firsova whotook part in the coring campaign at Arctic lakes in 2009. This study was supported bygrants Program of the RAS No 21.7, MD-4389.2009.5
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