Sampling was conducted with a TV-guided multiple corer (MUC), in order to retrieve undisturbed sediment cores. Upon retrieval of the MUC, the overlying water was carefully removed from each core and the core was cut into the following sediment horizons using a steel plate and a custom-made plastic ring: 0-1 cm, 1-5 cm, 5-10 cm. At each station, sediment samples from three replicate cores were pooled and transferred to a cooling container (0°C), where subsamples for extracellular enzymatic activity analyses were taken. The potential extracellular enzymatic activities of the hydrolases beta-glucosidase, chitobiase, aminopeptidase and extracellular enzymes acting as esterases were determined in alignment with Boetius and Lochte, 1994 (https://doi.org/10.3354/MEPS104299) and Boetius & Damm 1998 (https://doi.org/10.1016/S0967-0637(97)00052-6). The method uses small substrate proxies linked to a fluorophore. When the fluorophore is cleaved from the substrate, enzymatic hydrolysis is measured as an increase in fluorescence with time. Determinations of extracellular enzymatic activities were performed in triplicate for all samples with a Hitachi F-2000 spectrofluorometer.

The substrates and final concentrations used in the assays were the following:100 µM 4-Methylumbelliferyl ß-D-glucopyranoside to measure the activity of beta-glucosidases.100 µM 4-Methylumbelliferyl N-acetyl-ß-D-glucosaminide to measure the activity of chitobiases .500 µM L-Leucine-7-amino-4- methylcoumarin hydrochloride to measure the activity of aminopeptidases.100 µM Fluorescein diacetate to measure the activity of esterases.