Abstract
Permafrost distributed in the Arctic and in the elevated interior of Mongolia is projected to be particularly vulnerable to future global warming, where surface air temperatures are expected to rise several times faster than the global average. These regions also experienced substantial warming during the mid-Holocene Thermal Maximum, suggesting the potential destabilization of permafrost in the past. Reconstructing the state of permafrost during this warm period is therefore essential for improving future projections of permafrost-climate feedbacks.Lake sediments serve as valuable archives for terrestrial paleoclimate reconstruction. However, in permafrost regions where vegetation diversity is low, conventional proxies such as pollen are often insufficient to capture temperature variations or thawing dynamics of the active layer. To address this, we conducted sediment core sampling from lakes in the Alaskan Arctic and the Mongolian Plateau, supported in part by the Torii-Inoue Fund.Preliminary analysis revealed the presence of alkenones biosynthesized by haptophyte algae of the order Isochrysidales in some cores. As rare terrestrial temperature proxies, these biomarkers enable quantitative reconstruction of past surface temperatures. We aim to reconstruct mid-Holocene warming and associated permafrost responses using alkenone-based paleothermometry. In addition, we explore specific biomarkers produced during active layer thawing, with the goal of establishing molecular indicators for permafrost destabilization in the past.
