Diesels and lubricants used at research stations can persist in terrestrial and marine sediments for decades, but knowledge of their effects on the surrounding environments is limited. In a 5 year in situ investigation, marine sediment spiked with Special Antarctic Blend (SAB) diesel was placed on the seabed of O'Brien Bay near Casey Station, Antarctica and sampled after 5, 56, 65, 104 and 260 weeks. The rates and possible mechanisms of removal of the diesel from the marine sediments are presented here. The hydrocarbons within the spiked sediment were removed at an overall rate of 4.7mg total petroleum hydrocarbons kg(-1) sediment week(-1), or 245mgkg(-1)year(-1), although seasonal variation was evident. The concentration of total petroleum hydrocarbons fell markedly from 2020±340mgkg(-1) to 800±190mgkg(-1), but after 5 years the spiked sediment was still contaminated relative to natural organic matter (160±170mgkg(-1)). Specific compounds in SAB diesel preferentially decreased in concentration, but not as would be expected if biodegradation was the sole mechanism responsible. Naphthalene was removed more readily than n-alkanes, suggesting that aqueous dissolution played a major role in the reduction of SAB diesel. 1,3,5,7-Teramethyladamantane and 1,3-dimethyladamantane were the most recalcitrant isomers in the spiked marine sediment. Dissolution of aromatic compounds from marine sediment increases the availability of more soluble, aromatic compounds in the water column. This could increase the area of contamination and potentially broaden the region impacted by ecotoxicological effects from shallow sediment dwelling fauna, as noted during biodegradation, to shallow (<19m) water dwelling fauna.