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The Arctic is a region that is particularly vulnerable to climate change, as it is warming at a much faster rate than the rest of the globe. This warming causes a decline in multiyear sea ice cover, which results in an increase in ice-free waters with a much lower albedo compared to ice, therefore leading to a positive feedback and enhanced warming. Another factor that plays a role in regulating the temperature in the Arctic is the type and extent of cloud cover. Aerosols, that can serve as cloud condensation nuclei or ice nucleating particles (INPs), are key for cloud formation and aggregation state of water; liquid or ice. Some microorganisms produce INPs, but it is not well understood which microorganisms are most relevant, which environments they inhabit, and how active they are. In this study, we investigated the partitioning of INPs between the Arctic marine and atmospheric environment by combining in situ measurements with laboratory experiments, deploying cold-stage INP measurements and amplicon sequencing of the bacterial and eukaryotic communities. First, we determined if sea ice acts as a reservoir for INPs and, whether the INPs are partitioned into the sea ice during its formation or whether they are produced by microorganisms within the sea ice. We used a modified ice-finger to grow sea ice using sea water collected in West Greenland. We found that INPs are not enriched in the ice, but they stochastically incorporate into the ice fraction during sea ice formation. Next, we studied the temporal and spatial dynamics of INPs in Arctic sea ice cores that were collected before and during the spring sea ice phytoplankton bloom. We observed a higher concentration of INPs active at -10 C (INP-10) present towards the bottom of the sea ice core with concentrations 10-100-fold higher than those in the under-ice water. Finally, we determined the potential of sea-ice as a source of atmospheric INP. In separate experiments, we filled bulk water and water from melted sea ice from Nuuk and Station Nord into a temperature-controlled sea spray simulation chamber and quantified the microorganisms and INPs present in the bulk water and air before and after the water bubbling. We observed that the highly active INPs are efficiently aerosolized by bubble-bursting together with specific bacterial and eukaryotic taxa. In light of these findings, this study provides new insights into the role of Arctic sea ice as a reservoir for INPs and the microorganisms that potentially produce them. Additionally, it explores the mechanisms by which INPs are released into the Arctic atmosphere. Last, these results can be used to improve cloud and climate model predictions in the Arctic region.
Jensen et al. (Fri,) studied this question.