Ninth International Conference on Permafrost ... - IARC Research

The Combined Isotopic Analysis of Late Quaternary Ice Wedges and Texture Ice atthe Lena-Anabar Lowland, Northern SiberiaAlexander DereviaginMoscow State University, Faculty of Geology, Vorobievy Gory, 119899, Moscow, RussiaHanno MeyerAlfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam,Telegrafenberg A43, 14473 Potsdam, GermanyAlexander ChizhovMoscow State University, Faculty of Geology, Vorobievy Gory, 119899, Moscow, RussiaDiana MagensAlfred Wegener Institute for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, GermanyIntroductionDifferent types of ground ice are fed by meteoric watersources and are considered to be a unique archive of paleoenvironmentaland paleoclimatic information (Mackay 1983,Meyer et al. 2002). The isotopic signal of an ice wedge isindicative for winter temperatures. Texture ice (both segregatedand pore ice) may be assumed as a mixture of summerand winter precipitation. Isotope variations within sedimentcolumns are difficult to interpret in paleotemperature terms,because of various processes involved such as seasonalityof precipitation, amount of rain and snow feeding the activelayer, fractionation during evaporation, melting and freezingmay influence its isotopic composition. This study focuseson the combined isotopic analysis of Late Quaternary icewedges and texture ice in an ice-rich sedimentary complexnamed Ice Complex. The isotopic composition (δ 18 O, δD) ofground ice dating to ca. 60 ka was studied in the frameworkof Russian-German multidisciplinary research expeditionsat the Laptev Sea coast.Study Sites and MethodsThe investigations were carried out at two sites locatedin the Lena-Anabar lowland at the Laptev Sea coast atBykovsky Peninsula (eastern part of Lena Delta): atMamontovy Khayata outcrop, 71°60′N, 129°20′E (site 1)and at Cape Mamontov Klyk, 73°36′N, 117°10′E (site 2).The region is characterized by a continental Arctic climate.Mean annual air temperatures (MAAT) at site 1 are about-14°C, mean January temperatures (T J) are about -34°C andmean winter temperatures (T w) are about -22°C (data ofTiksi). MAAT at site 2 are about -15°C, T Jare about -33°C,and T ware about -23°C (data of Cape Terpey-Tumasa).Annual precipitation reaches 300 mm, with a maximum(about 75%) in summer. The region belongs to the zone ofcontinuous permafrost with a thickness of about 300–500m and mean annual ground temperature around -12°C. Thecoastal lowland is characterized by widespread Ice Complexremains, composed of ice-rich silty fine-grained sand withpeaty paleosol horizons and huge syngenetic polygonalice wedges (heights of 20–40 m and widths of 2–6 m) andcolumns of frozen sediments (width of 2–4 m) with belt-likecryostructure.The formation of Late Pleistocene Ice Complex is usuallyassociated with Karginsky and Sartansky periods of theRussian stratigraphy, which correspond to MIS-3 and MIS-2of the global classification. According to AMS dates, IceComplex formation at Bykovsky Peninsula was between58.4 ka (at sea level) and 12.2 ka BP (Schirrmeister et al.2002). At Cape Mamontov Klyk, Ice Complex formationtook place between 31–28 ka and 10.7 ka BP (Schirrmeisteret al. 2008). At both sites, Ice Complex is partly covered by a2 m thick horizon of peat-rich, silty sediments with Holoceneice wedges. Holocene ground ice was also studied in alases,thermo-erosional and river valleys.The investigations are based on the combined applicationof stable isotopes to both ice wedges and texture ice sampledin parallel. Measurements of isotope composition (δ 18 O, δD)were carried out at the Alfred Wegener Institute in Potsdam.The stable isotopic composition is given in ‰ vs. V-SMOWstandard. The 1σ errors for H and O isotopes are better than0.8‰ and 0.10‰, respectively.Results and DiscussionThe available data of isotope analyses are presented inTable 1. Both wedge and texture ice differs considerably intheir isotopic composition between Holocene and Pleistocene,with 3–8‰ lower δ 18 O in Pleistocene ice following theglobal warming trend. The isotopic composition of bothLate Pleistocene wedge and texture ice is very close at site 1and site 2. This can be evidence both of the similarity of icecomplex formation and climatic conditions in the region.The mean δ 18 O of ice wedges differs by 0.1‰ in Sartansky(MIS-2) time, and by 1.6‰ in Karginsky (MIS-3) timebetween both sites. For texture ice, the differences areabout 0.1‰ in Karginsky time. In Holocene, differences inmean δ 18 O reach about 3‰ for ice wedges and 0.7‰ fortexture ice between both sites. The observed differences ofHolocene ice wedges are likely the result of different agesof the sampled ice wedges at sites 1 and 2. At site 1, manyEarly Holocene ice wedge samples were taken at the top ofthe Ice Complex.The ice wedge isotopic composition is similar in Karginskyand Sartansky with more negative minimum values (of -33.9to -34.9‰) in Karginsky time. This leads to the assumption61