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Primary biological aerosol particles and microorganisms are ubiquitous in the atmosphere. Investigations of airborne chemical markers and microbial communities are critical for identifying sources, transport and transformation processes of aerosols. One potential major source of airborne chemical compounds and microbial communities (e.g. L- and D-amino acids, Flavobacteria) could be related to phytoplankton blooms that occur during the spring season in Arctic fjord systems. Here, we conducted a field study in a polar environment to investigate the occurrence in coarse and fine particles of water-soluble compounds (major ions, carboxylic acids and free L- and D-amino acids) and airborne bacterial communities in aerosol samples. The sampling was conducted with a 6 day sampling frequency at the Gruvebadet observatory, close to Ny-Ålesund (Svalbard Islands). Glycine, D-amino acids and C4- organic acids increased during the exponential phase of a marine bloom that occurred in Kongsfjorden and started to drop at the beginning of the main-bloom phase. On the other hand, Polaribacter together with free L-amino acids overlapped with the Chlorophyll a peak and the subsequent decline, and thus might constitute a useful marker for the main-bloom phase.

Ecological stability under environmental change is determined by both interspecific and intraspecific processes. Particularly for planktonic microorganisms, it is challenging to follow intraspecific dynamics over space and time. We propose a new method, microsatellite PoolSeq barcoding (MPB), for tracing allele frequency changes in protist populations. We successfully applied this method to experimental community incubations and field samples of the diatom Thalassiosira hyalina from the Arctic, a rapidly changing ecosystem. Validation of the method found compelling accuracy in comparison with established genotyping approaches within different diversity contexts. In experimental and environmental samples, we show that MPB can detect meaningful patterns of population dynamics, resolving allelic stability and shifts within a key diatom species in response to experimental treatments as well as different bloom phases and years. Through our novel MPB approach, we produced a large dataset of populations at different time‐points and locations with comparably little effort. Results like this can add insights into the roles of selection and plasticity in natural protist populations under stable experimental but also variable field conditions. Especially for organisms where genotype sampling remains challenging, MPB holds great potential to efficiently resolve eco‐evolutionary dynamics and to assess the mechanisms and limits of resilience to environmental stressors.

New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low-volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion-induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice-covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.

The potential for adaptation of phytoplankton to future climate is often extrapolated based on single strain responses of a representative species, ignoring variability within and between species. The aim of this study was to approximate the range of strain-specific reaction patterns within an Arctic diatom population, which selection can act upon. In a laboratory experiment, we first incubated natural communities from an Arctic fjord under present and future conditions. In a second step, single strains of the diatom Thalassiosira hyalina were isolated from these selection environments and exposed to a matrix of temperature (38C and 68C) and pCO2 levels (180 latm, 370 latm, 1000 latm, 1400 latm) to establish reaction norms for growth, production rates, and elemental quotas. The results revealed interactive effects of temperature and pCO2 as well as wide tolerance ranges. Between strains, however, sensitivities and optima differed greatly. These strain-specific responses corresponded well with their respective selection environments of the previous community incubation. We therefore hypothesize that intraspecific variability and the selection between coexisting strains may pose an underestimated source of species’ plasticity. Thus, adaptation of phytoplankton assemblages may also occur by selection within rather than only between species, and species-wide inferences from single strain experiments should be treated with caution.