oa GDGT-Based Fingerprints in the Amundsen Sea Embayment: Insights into Climatic and Environmental Conditions in a Polar Environment

The West Antarctic Ice Sheet (WAIS), particularly the Amundsen Sea sector, has undergone significant ice loss over recent decades, largely driven by warm Circumpolar Deep Water (CDW) intrusions that enhance sub-ice shelf melting and grounding-line retreat. Understanding past oceanic influences on WAIS dynamics is crucial for predicting future stability. This study investigates lipid biomarkers in surface sediments from the Amundsen Sea shelf, collected during the THOR NBP19-02 and NBP20-02 expeditions, to assess environmental controls on GDGT-based paleotemperature proxies. We applied TEX₈₆ variants, BIT, Methane Index (MI), IR6Me, and GDGT-0/crenarchaeol ratios to evaluate seawater temperature, redox conditions, and organic matter sources. Results indicate a cold, oxic depositional environment with limited terrestrial and methanogenic input, supporting Thaumarchaeota as the dominant GDGT source. Local anomalies, such as diatom-rich sediments in Cranton Bay, reflect episodic CDW upwelling and variable biological productivity. TEX₈₆ᴸ-derived sub-surface ocean temperatures (-0.9 to 2.1 °C) confirm regional cold-water dominance with localized CDW influence. Our findings highlight the potential of biomarker proxies for reconstructing seawater temperatures in Antarctic settings and provide new insights into the spatial variability of environmental drivers affecting WAIS stability.