batch_auto_20260713 202607131256465730 BOEM ESP geoESPIS ESPIS@boem.gov Bureau of Ocean Energy Management Investigating the impacts of oil exposure and changing snow cover on sea ice microbial communities University of Alaska Fairbanks University of Alaska Fairbanks To understand the potential effects of the dual anthropogenic impacts of thinning sea ice/snow and potential crude oil spills from increased oil and gas exploration, we isolated four sea ice diatoms from sea ice cores collected near Utqiagvik, Alaska. The growth and maximum cell concentrations of four sea ice diatom isolates (Attheya septentrionalis, Fragilariopsis cylindrus, Synedropsis hyperborea strains 1 and 2) were determined in a full-factorial design experiment with five irradiances (3–125 µmols photons m-2 s-1) and twelve concentrations (0–8.7 mg L-1) of Alaska North Slope (ANS) crude oil. These data were used to calculate ANS crude oil concentrations for 10% and 50% inhibition of growth (IC10 and IC50). F. cylindrus was the most sensitive to ANS crude oil contamination with exponential growth IC10 of 1.4–5.3 mg L-1. There was evidence of interactions between ANS crude oil impact and irradiance; A. septentrionalis had a significantly lower IC10 (higher sensitivity) under the highest irradiance while other strains had increasing IC10 (lower sensitivity) with increasing irradiance for some measures. These data were combined with in situ observations of sea ice thickness and irradiance to create a 1D model to assess how a potential oil spill would impact sea ice algal biomass and diversity under different snow conditions. We found that algal diversity and biomass both decreased in a simulated ANS crude oil spill in the Alaskan Arctic, particularly under low snow conditions. Transcriptome and metatranscriptome experiments from sea ice diatom isolates and natural sea ice microbial communities were performed to assess the gene expression changes under oil contamination at different irradiances. 298112 U.S. Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies Program https://doi.org/10.13039/100012475 M20AC10007 10.67297/9A1E5D https://boem.gov/awardpages/100317