Grass on the shores of Lake El'gytgytgyn Lake El'gygytgyn ice Snow arch at Lake El'gygytgyn

Addie Rose Holland

Graduate Research

My interests lie in paleoclimatology - reconstructing past climates through the study of natural records, particularly the biogeochemistry of lake sediments. For my Master's research, I was involved in the Lake El'gygytgyn Drilling Project in Northeast Siberia. The sediments of Crater Lake El'gygytgyn have been collected in order to gain high-resolution data stretching continuously over the last ~3.6 million years.

Exploring Isotopic Signatures of Lake El'gygytgyn Sediments for Evidence of Anoxia and Methane Cycling over the Past 50,000 Years

As we embark on a new age of future climate uncertainty and the body of evidence grows for current and recent global changes in climate, it becomes increasingly important to expand our understanding of how climate change impacted the natural landscape in the past. Currently, polar regions are gaining both scientific and public interest because of their vulnerability to changing climate as well as the potential global impacts resulting from polar change if rapid warming continues unabated. The particular sensitivity of Arctic regions presents them as important recorders of past climate because summer temperatures in these regions hover near freezing, thus small changes in warming may cause large changes in environmental response. Arctic lakes provide evidence of changes in the terrestrial environment through accumulated sediment, which partially documents conditions of life and erosion within the lake basin. Impact Crater Lake El'gygytgyn (67°N) contains a continuous sediment record since the time of impact approximately 3.6 Myr BP. Studies of Beringian glaciation have revealed that the area around the lake has not been glaciated since impact, and thus has not experienced glacial erosion or interruption in sedimentation. The long and continuous sedimentation record makes Lake El'gygytgyn unique because most high-latitude lakes experience ephemeral periods of existence and therefore colonization and extinction of flora and fauna within their waters. Thus, Lake El'gygytgyn holds promise to provide a long term, continuous record of climate and ecosystem change in the high Arctic from Pliocene to the present.

Abstract

Compound specific isotope analysis of lake sediments is a powerful tool in deciphering evidence of changing climatic and paleoenvironmental conditions through time. Isotopic analysis of Lake El'gygytgyn pilot sediment cores, PG1351 and LZ1029, have contributed increased insight into paleoenvironmental interpretations regarding conditions of permanent ice cover and water column anoxia at the lake over the past 250 kyr. Bulk sediment δ15N was measured as a proxy for denitrification and a possible indicator for water column anoxia intensity. However, it appears that insufficient quantities of water column nitrate to fuel denitrification make its correlation with anoxia intensity ineffective. In pilot core LZ1029, compound-specific δ13C of alkanes, fatty acids, and alcohols were analyzed to determine the changing sources of organic matter as well as the source of a strong negative isotopic shift in the bulk sediment δ13C (-26‰ to -33‰) over the past 50 kyr. Results indicate that the majority of alkanes, fatty acids, and alcohols are long chain compounds consistent with a terrestrial plant origin, with increased aquatic contribution during the local last glacial maximum (LLGM). Among the compound classes examined, only the mid chain fatty acids display a strong LLGM depletion (δ13C = -43‰). Short chain fatty acids exhibit an LLGM depletion (δ13C = -35‰) similar to bulk sediment δ13C, while the δ13C trend of long chain alkanes, fatty acids, and alcohols differ from the bulk sediment δ13C trend, suggesting an autochthonous source of bulk isotope depletion. Evidence of methane cycling exists only in the presence and isotopic value of diplopterol (LLGM δ13C = -93.4‰), a biomarker for aerobic oxidation of methane. Two compounds indicative of archaeal lipids were present at considerable concentrations during the LLGM (394 and 668 µg/g TOC), but without the extreme negative δ13C associated with methanogenesis and methanotrophy. These results suggest insufficient generation of methane in the lake to have derived from such a large anaerobic archaeal methanogen community suggesting that archaea are not acting entirely as methanogens. Furthermore, it appears unlikely that a significant anoxic layer existed in the water column of Lake El'gygytgyn during the past ~50kyr. The results of this work will be applied to ongoing investigations on the newest cores from Lake El'gygytgyn, which represent the past 3.6 Myr.

Full copy of Master's thesis available at: UMass Library Scholarworks page

Advisor: Julie Brigham-Grette

Lab Director: Steven Petsch

Student collaborator: Kenna Wilkie

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