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The diatom oxygen isotope record from Lake El’gygytgyn, NE Russia - Arctic climate history of the last three glacial-interglacial cycles

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Meyer, H. , Chapligin, B. and Hubberten, H. W. (2012): The diatom oxygen isotope record from Lake El’gygytgyn, NE Russia - Arctic climate history of the last three glacial-interglacial cycles , APEX VI International Meeting and Workshop, Oulanka, Finland, 14 May 2012 - 18 May 2012 .
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Abstract:

The Arctic became a region of growing interest for (paleo)climate researchers within the last decade (IPCC, 2007). However, continuous paleo-climate records in the continental Arctic region are rare, especially beyond the Last Glacial Maximum (LGM). At Lake El’gygytgyn, NE Siberia sediment cores were retrieved in an area, which has not been glaciated since the Pliocene. Here, inside a crater structure formed by a meteorite impact circa 3.6 Ma ago (Layer, 2000), a continuous sediment record was deposited. Lake El’gygytgyn is of circular shape, about 12 km in diameter and 170 m deep. This cold-monomictic and ultra-oligotrophic lake has a small catchment (293 km2) and only one outflow. Due to the absence of carbonates in the lake, we used the oxygen isotopic composition of biogenic silica (diatoms) for paleoclimate reconstruction. The usefulness of diatoms and their δ18O values as a proxy for reconstructing air temperatures and/or the isotope composition of precipitation has been widely demonstrated (e.g. Leng & Barker, 2006). Preliminary studies have shown that mainly two diatom species are present in the lake: Cyclotella ocellata which occurs throughout the whole core and Pliocaenicus costatus mainly existing in the Holocene. Various preparation steps (H2O2/HCl treatment, sieving, heavy liquid separation) have been performed in order to gain a clean diatom sample from the original sediment. The <10μm fraction was used showing mostly a mono-specific diatom assemblage of Cyclotella ocellata. More than 95% of the samples showed a degree of purity of SiO2 > 97 %. In a first step, we have analysed δ18O diatom of 96 samples (N=2-4) from shallow sediment core Lz1024 (16.5 m long) dating back to app. 250 ka. Special emphasis was laid on the time periods between 0-20ka BP (resolution ~ 1k) and 120-250ka BP (resolution ~ 3k). The standard deviation between the repetitions was 1σ < ±0.3 ‰. The downcore variations of the δ18O values show that glacial-interglacial cycles are present throughout the whole core. The δ18O values range from δ18O = +19.1‰ to +24.4‰ and reflect the Holocene Thermal Maximum (HTM; δ18O = +23‰; 8.9 ka), the Last Glacial Maximum (LGM; δ18O = +19.1‰; 23.1 ka), the Eemian interglacial period (δ18O = +24.4 ‰; 127.2 ka), the interval corresponding to MIS 7.1, 7.3 (plateau around +23.0‰, ~209-203 ka) and MIS 7.5 (+23.6‰; 243.9 ka). A peak-to-peak amplitude of 5.3‰ between the MIS 5.5 absolute maximum and the LGM absolute minimum was detected, most likely controlled by the δ18O signal of precipitation. This is the longest continuous terrestrial δ18O record from the Arctic directly reflecting paleo precipitation signals. Correlations of the δ18O record with the benthic stack LR04 (Lisiecki and Raymo, 2005; r=0.58) and EPICA Dome-C δD record (EPICA members, 2004; r=0.69) are significant and show the sensitivity of Lake El’gygytgyn and the wider Arctic climate system to global climate change. By the time of the conference, this work will be expanded to the long lake sediment core 5011-1 (dating back to about 3.6 Ma), which was drilled within the ICDP programme at Lake El’gygytgyn in early 2009. EPICA members: Eight glacial cycles from an Arctic ice core, Nature, 429, 623-628, 2004. Layer, P. W.: Argon-40/argon-39 age of the El'gygytgyn impact event, Chukotka, Russia, Meteoritics & Planetary Science, 35, 591-599, 2000. Leng, M. J., and Barker, P. A.: A review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction, Earth-Science Reviews, 75, 5-27, 2006

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