Linking Biogenic High-Temperature Ice Nucleating Particles in Arctic soils and Streams to Their Microbial Producers

Abstract. Aerosols, including biological aerosols, exert a significant influence on cloud formation, influencing the global climate through their effects on radiative balance and precipitation. The Arctic region features persistent mixed-phase clouds, which are impacted by ice nucleating particles (INPs) that modulate the phase transitions within clouds, affecting their lifetime and impacting the region's climate. An increasing number of studies document that Arctic soils harbour a large number of biogenic INPs (bioINPs), but these have yet to be linked to their microbial producers. In addition, the transfer of bioINPs from soils into freshwater and marine systems has not been quantified. This study aimed at addressing these open questions by analyzing soil and freshwater samples from Northeast Greenland to determine the microbial composition along with the INP concentrations and size distributions. We found that soils contained between 3·10⁴ and 6·10⁶ INP g^-1 soil, which was on the lower side of what has previously been reported for permafrost soils. The composition of INPs varied widely across locations and could have originated from bacterial and fungal sources. We found that Mortierella, a fungal genus known to produce ice-nucleating proteins, was present in nearly all samples. Spearman correlations between soil taxa and INP concentrations pointed at lichenized fungi as a possible contributor to soil INP. Additionally, based on the INP size distribution, we suggest that soil INPs were bound to soil particles or microbial membranes at some locations, while other locations showed a variety of soluble INPs with different molecular sizes. In streams, INP concentrations and onset temperatures were comparable to what has previously been measured in streams from temperate regions. Interestingly, stream INP concentrations showed a positive association with soil INP concentrations. The potential release and aerosolization of these bioINPs into the atmosphere—whether directly from the soil, from streams into which they are washed, or from the oceans where they might be transported—could significantly impact cloud formation and precipitation patterns in polar regions. The presence of highly active INPs in Arctic regions holds implications for mixed-phase cloud properties and climate, revealing the significant, yet complex, role that soil and stream bioINPs play in the Arctic climate system. This research contributes valuable knowledge to the understanding of microbial communities and the potential producers of highly active bioINPs in Arctic soil microbial communities and their connectivity with Arctic streams.