Ice nucleating properties of airborne dust from an actively retreating glacier in Yukon, Canada

Airborne dust from glacier outwash sediments may alter properties of clouds and climate at high latitudes by acting as ice nucleating particles (INPs). Nevertheless, the ice nucleating ability of airborne dust from glacier outwash sediments remains uncertain. To address this uncertainty, we measured the ice nucleating ability of airborne dust near an actively retreating glacier in Yukon, Canada during a period when airborne dust concentrations were well above background levels. The airborne dust caused freezing at temperatures from -6 to -23 °C. At temperatures colder than -15 °C, the ice nucleating ability of the airborne dust was similar (within 1 order of magnitude in terms of ice active site density) to that of K-feldspar and Icelandic dust. However, the ice nucleating ability of the airborne dust was significantly worse than the glacier outwash sediments collected in Svalbard by Tobo et al. (2019). Based on a heat assay and an ammonium sulfate assay, the INPs from the airborne dust that caused freezing at temperatures warmer than -15 °C likely contained biological materials. We show that airborne dust from the retreating glacier led to high concentrations of ice nucleating particles at the site for at least most of May 2018, which were two orders of magnitude higher than a prediction using a global chemical transport model that includes low latitude dust sources and anthropogenic dust sources, but not natural high latitude dust sources.