Seafloor deposition of water-based drill cuttings generates distinctive and lengthy sediment bacterial community changes.

The spatial extent and persistence of bacterial change caused by deposition of water-based drill cuttings on the seafloor were explored by a community-wide approach. Ten centimeter sediment cores were sampled along transects extending from ≤15 m to 250 m from three nearby drilling sites in the southern Barents Sea. Eight months, 8 years and 15 years, respectively, had passed since the completion of the drillings. At locations heavily affected by drill cuttings, the two most recent sites showed distinct, corresponding deviances from native Barents Sea bacterial community profiles. Otherwise marginal groups, including Mollicutes and Clostridia, showed significant increases in relative abundance. Beyond 100 m from the boreholes the microbiotas appeared undisturbed, as they did at any distance from the 15-years old borehole. The extent of the biological distortion, as indicated by the present microbial study, agreed with previously published macrofaunal surveys at the same drilling sites. • Water-based drill cuttings affect seafloor bacterial community composition. • Bacterial community changes only observed within 100 m from the drilling site. • The bacterial perturbations may last for more than 8 years after drilling. • A few groups of bacteria, marginal in the native marine sediments, proliferated. [ABSTRACT FROM AUTHOR]