Hydrolysable amino acids in sediments from the Porcupine Abyssal Plain, northeast Atlantic Ocean

The distributions of hydrolysable amino acids have been examined in replicate sediment cores from the Porcupine Abyssal Plain in the northeastern Atlantic Ocean. The amino acid concentrations in surficial sediments ranged from 11.4 to 12.6 μmol g−1 dry sediment, with a mean of 11.8 μmol g−1 dry sediment, and decreased with increasing sediment depth, but showed a marked maximum between 20 and 40 mm, albeit with significant variability in their abundance at that depth. Normalisation of the concentrations of hydrolysable amino acids to total organic carbon showed that the organic matter at the surface and in the sub-surface maximum was relatively fresh. The vertical concentration profiles of hydrolysable amino acids were also reflected by organic carbon and total nitrogen and are attributed to the transfer of relatively fresh organic matter from the sediment surface by bioturbation, probably by large detritovores. The depth of the zone of bioturbation (i.e. ≈40 mm) is consistent with the zone of maximum biological activity in the Porcupine Abyssal Plain sediments.