Seasonal Dynamics of Bioaerosols and Ice Nucleating Particles in the High Arctic Atmosphere

The Arctic is experiencing rapid climate change, with warming rates four times higher than the global average. This warming has a profound impact on the Arctic hydrological cycle, including cloud formation and precipitation processes. Bioaerosols are critical components driving these processes as they can act as high-temperature ice nucleating particles (INPs). Despite their importance, the representation of bioaerosol-cloud interactions in climate models remains highly uncertain, primarily due to limited understanding of biogenic INPs, their sources and specific properties. Recent studies have highlighted the need for long-term studies and detailed source characterization of INPs and their characteristics in the Arctic to bridge these knowledge gaps.

Here, we present preliminary data from the first long-term dataset of bioaerosol concentration and composition in the High Arctic, complementing detailed high-temperature INP measurements. The samples were collected at the Villum Research Station in North Greenland over three years (2021–2023) at a time resolution of 3.5 days. INP concentrations were measured using the Micro-PINGUIN cold-stage setup, focusing on activity between 0°C and -20°C. Simultaneously, bacterial communities in the air were characterized through qPCR and 16S rRNA gene amplicon sequencing. Source-tracking analyses were performed using potential environmental sources, including soils, glacial runoff, plant material, and seawater, supplemented with publicly available Arctic sequence datasets. Meteorological data and aerosol microphysical and chemical data, such as black carbon and particle number size distributions, were incorporated to support the analysis of bioaerosol drivers.

Preliminary results reveal that INP_-12 concentrations ranged from 2.2 • 10^-5 to 7.2 • 10^-2 • L^-1, consistent with previous observations in the High Arctic. Airborne bacterial concentrations were exceedingly low, ranging from 2.7 • 10⁰ to 4.2 • 10³ • m^-3 of air, and the taxonomic diversity varied seasonally. During the Arctic haze season, the microbial community was dominated by spore-forming taxa, such as Bacillus, likely transported via long-range atmospheric transport from mid latitudes. In contrast, post-haze conditions were marked by increased microbial diversity, dominated by phototrophic taxa such as Tychonema and other members of the core cryospheric microbiome, including Sphingomonas and Hymenobacter. These taxa likely originated from regional terrestrial and marine sources, exposed to the atmosphere as snow and ice melted during summer. Both bacterial concentrations and the taxonomic diversity were positively correlated with the warm-temperature INP concentrations (ρ = 0.66, p = 3.6 • 10^-12 and ρ = 0.59, p = 1.2•10^-9,  respectively), suggesting a direct link between bioaerosol abundance and INP concentration in the Arctic atmosphere. Finally, Spearman rank correlations also revealed significant relationships between warm-temperature INP concentrations and the relative abundances of 177 microbial genera, giving insights into the potential sources of these INPs.

These findings provide new insights into the seasonal dynamics of bioaerosols and their role as INPs in the High Arctic. Our long-term dataset highlights the importance of integrating microbial ecology, aerosol microphysics and chemistry, and meteorological observations to improve our understanding of aerosol-cloud interactions. Future work will focus on disentangling the contributions of source environments and microbial taxa to Arctic INP populations, with the goal of refining aerosol-cloud interaction parameterizations in climate models.