Ice-nucleating particles in Greenlandic glacial outwash plains

Abstract. High-latitude dust (HLD) represents a source of ice-nucleating particles (INPs) with potential impacts on cloud formation and radiative forcing in the Arctic. Previous studies have shown that HLD can exhibit high ice-nucleating activity at high subzero temperatures, likely linked to a biological component. Yet, comprehensive assessments of HLD ice-nucleating characteristics and sources remain limited, especially in Greenland. Here, we show that glacial dust from three outwash plains in southwestern Greenland effectively nucleates ice at temperatures relevant for mixed-phase clouds, but with lower ice-nucleating activity than other HLD regions. Ice-nucleating activity of glacial dust shows high variability and is largely driven by small amounts of organic and biological material, as indicated by sample treatments and positive correlations of ice-active mass site densities with total organic carbon and microbial abundance. Atmospheric INP concentrations above -20 °C were higher at the outwash plain sites compared to a nearby fjord site, indicating localized influence under summertime background conditions. This is further supported by similarities between atmospheric and dust INP spectra, as revealed by principal component analysis. The atmospheric INP population was dominated by organic and biological contributions, with no clear role of local meteorology or long-range transport. Overall, the ice-nucleating activity of glacial dust in southwestern Greenland lies within the lower range of reported HLD INP activity, suggesting that highly active HLD parameterizations may overestimate INP concentrations in this region. This highlights the importance of region-specific dust characterizations for improving representation of cloud processes and climate impacts in the Arctic.