Depletion of crude oil and fuel in the Arctic. Summer and winter field studies with immobilized oil in seawater at Svalbard.

Seasonal dynamics can vastly influence the natural depletion of oil spilled into the ocean and the Arctic regions are characterized by large seasonal changes, especially in temperature and daylight. To determine the influences of seasonal variation on natural oil depletion processes like dissolution, photooxidation and biodegradation, we deployed thin films of three oils in natural seawater during the Arctic summer and winter in Svalbard, Norway. The extent of oil depletion varied with season and the type of the oil, however, considerable depletion of n-alkanes and polycyclic aromatic compounds were observed during both summer and winter. The influence of temperature on depletion of components was not consistent between the three oils and only small effects of photooxidation were found during the summer. We further found variations in the composition of bacterial communities associated with the oil films between the seasons with an apparently delayed succession during the winter. The bacterial communities generally contained high abundances of previously reported oil degrading taxa which displayed distinct seasonal patterns in their relative abundance. Oleispira and Oleibacter were dominantly found during the summer and Colwellia during the winter, while Cycloclasticus and C1-B045 were highly abundant during both seasons. While the environmental factors were likely the cause for variations in oil depletion between the seasons and oils, the seasonal differences in the bacterial community composition did not seem to affect their biodegradation potential.