Reconstructing past Arctic sea ice and permafrost changes with lipid biomarkers: proxy development and case studiesdissertationsWang, Karen JiaxicreatorHuang, YongsongAdvisorClemens, StevenReaderHerbert, TimonthyReaderTsai, VictorReaderKartzinel, TylerReaderO'Donnell, JonathanReaderBrown University. Department of Earth, Environmental, and Planetary Sciencessponsor2022xv, 207 p.born digitalThesis (Ph. D.)--Brown University, 2022thesesThe Arctic is warming at an unprecedented rate, and the unique features of the Arctic, including sea ice and permafrost, are experiencing rapid changes. The Arctic sea ice cover has declined to its lowest level since at least 1850, exposing the dark seawater with low albedo and altering the Earth’s heat budget. On the other hand, permafrost thaw in the past decades has exposed previously frozen organic matter to microbial degradation, and emitted a significant amount of greenhouse gasses, which accelerate climate warming. However, modeling of sea ice and permafrost changes suffers from limited historical data and a lack of knowledge of the physical process. This dissertation aims to develop biomarker tools for sea ice and permafrost reconstructions with case studies and proxy validations. The first section of this dissertation focuses on the development of a novel alkenone-based sea-ice proxy by combining molecular biology and organic geochemistry methods. The second section of this dissertation focus on applying lipid biomarker proxies in Alaska maar lakes. I reconstructed the hydrological, ecological, and carbon-cycle changes in response to climate variations and permafrost thaw through downcore sediments since the late 1950s at high resolutions. In conclusion, this dissertation demonstrated the alarming rate of Arctic warming and the usefulness of lipid biomarker proxies.Sea icearctic paleoclimateAlaskalipid biomarkerPermafrostEnglishRPB20220706