Oleamide as a novel insoluble organic marker for reconstructing Arctic wildfire history in the ice core from southeastern Greenland

Abstract. Global warming has intensified boreal forest fires, which significantly influence the climate through the emission of greenhouse gases and organic aerosols (OA). While water-soluble tracers are commonly used to reconstruct past fire events in ice cores, they can be susceptible to redistribution or degradation within the ice matrix. In this study, we performed single particle analysis of non-volatile microparticles in the SE-Dome II ice core from southeastern Greenland (1799–2020) using micro-Raman spectroscopy and Fourier-transform infrared spectroscopy (FT-IR). Here, we report the first identification of oleamide, an insoluble fatty acid amide, within an ice core. Oleamide is likely formed through the dehydration condensation of plant-derived oleic acid and ammonia under high-temperature (300–500 °C) conditions during forest fires. The detection frequency of oleamide particles was notably higher in layers corresponding to major North American forest fires, such as those in 1908, 1961, and 1994. Due to its insolubility and chemical stability, oleamide serves as a robust tracer that ensures stable long-range transport and long-term preservation in ice sheets. Additionally, cooling experiments revealed that oleamide possesses low ice-nucleating ability, likely due to the formation of expanded-phase monolayers. These results establish oleamide as a powerful new insoluble organic marker for reconstructing Arctic wildfire history and understanding historical fire-climate interactions.