Abstract
This thesis investigated in situ oil depletion in temperate and Arctic seawater, focusing on how seasonal and locational changes influence biodegradation, photooxidation, and dissolution. Field trials in Trondheim, Vesterålen, and Svalbard used three oils deployed as thin films on Fluortex fabrics; a parallel Trondheim study compared these with oil-soaked clay beads, which showed slower depletion of n-alkanes and PACs, reflecting reduced oil accessibility.
Microbial biodegradation dominated n-alkane removal, which was often as fast—or faster—at low temperatures compared to higher ones and mainly co-occurred with high abundances of Oleispira and Oleibacter. PAC depletion was attributed to combined effects of biodegradation, dissolution of small, low-alkylated compounds, and photooxidation of larger, highly alkylated PACs. Biodegradation of PACs coincided with increases in Cycloclasticus, Colwellia, and C1-B045 following the decline of n-alkane–degrading genera. More viscous oils often displayed slower overall depletion, especially of PACs. Differences among oils, seasons, and locations should be considered in oil-spill response strategies, and extrapolations of biodegradation based solely on temperature may not accurately represent in situ conditions.