IMIS

To assess the potential for cable bacteria activity, sediment cores (60 mm internal diameter) were retrieved from three locations (Yarra River (Australia), Kobbefjord (Greenland), Long Island Sound (USA)) using a gravity core sampler. Prior to incubation the sediment was sieved over a 0.5 – 1mm mesh (Yarra River and Long Island Sound) or asphyxiated to remove possible present benthos (Kobbefjord, Greenland). Sieved sediments were homogenized and packed into plastic core liners (inner diameter 36 mm), adjusting the height of the sediment to the rim of the core liner (for ease of microsensor profiling). At the start of the laboratory incubation, sediment cores were submerged in an aquarium in a temperature-controlled climate room fixed at in situ temperature where possible. During laboratory inductions, the overlying water of the aquarium was continuously bubbled with ambient air to retain a fully oxygenated water column. At three timepoints after the start of the laboratory incubation, high resolution porewater depth profiles were measured using a pH, O2 and H2S microsensors (Unisense, Denmark).