Marine oil snow formation in microcosm incubations of artificial seawater at 4 °C

An oil spill in the Arctic would have far-reaching impacts on the environment, the biota, and the Inuit communities that depend on this unique ecosystem for their livelihoods. Due to the rapid retreat of sea ice in the region, the Arctic is becoming more vulnerable to oil spills. Since microorganisms are the first responders to oil contamination, understanding their behavior is critical for designing bioremediation approaches tailored to Arctic conditions. In this study, we conducted microcosm experiments at 4 °C in the dark to simulate an Arctic oil spill, using crude oil and diesel as hydrocarbon sources. Biostimulation was tested with the addition of nutrients NaNO3 and KH2PO4, and soy lecithin–Tween 80 dissolved in ethanol as an alternative dispersant. Microcosms were placed on tube rollers at 3 rpm to mimic natural wave action and run with appropriate controls to assess microbial community shifts. Our objectives were to characterize the early microbial succession associated with oil degradation and marine oil snow (MOS) formation, and to determine how nutrients, dispersants, oil type (crude vs. diesel), photochemical aging (fresh vs. weathered), and oil concentration influence these processes. We observed that the combined effect of nutrients and dispersant resulted in rapid MOS formation, occurring as early as 30 minutes after the initial setup. Microbial taxa exhibited varying tolerance to different concentrations of the same oil, and the dominant hydrocarbon degraders in fresh diesel treatments were distinctly different from those in weathered diesel. Furthermore, the nutrient–dispersant treatment promoted an earlier succession of oil-degrading taxa compared to nutrient-only or dispersant-only treatments. Together, these results highlight the importance of cold-adapted microbial communities in driving early oil degradation and MOS formation in Arctic waters, and they provide insights relevant to the development of Arctic-specific bioremediation strategies.