Methodology:

An SBE9Plus CTD was used to collect fluorescence data from three stations in the Scotia Sea, which was converted from volts into chl-a (µg l-1) using the manufacturer's calibration. Chl-a concentrations were used as a proxy for the relative primary productivity of each station. 12 litre Niskin bottles attached to a SBE11Plus deck unit collected water for faecal pellet (FP) analysis at the same stations. Six bottles were fired, at 5 m, 20 m, 40 m, 100 m, 200 m and 400 m. On deck, water was gently siphoned out of the Niskin bottles via a piece of silicone tubing, which had been pre-rinsed three times with 0.22 µm filtered seawater (FSW), into pre-rinsed 20 L carboys. To ensure collection of all possible faecal material from the funnelled base of the Niskin bottles, the base of each bottle was opened, rinsed with FSW, and the water collected in separate sterile 250 ml Nalgene bottles. The contents of the carboys and Nalgene bottles were then gently filtered through a 53 µm mesh and bottles rinsed through with FSW. The contents of the mesh were backwashed into a 250 ml sterile Nalgene bottle using a 5% borax-buffered formalin-seawater solution. For sample analysis, the contents of Nalgene bottles were filtered onto a 53 µm mesh, gently rinsed and backwashed into petri dishes. Petri dishes were examined under a light microscope (Olympus SZX16 with SDF PLAPO 0.5XPF and 1.6XPF objectives) for whole or fragmented faecal pellets and other organic matter (e.g. diatoms, protozoa and marine snow). FPs were photographed using a Canon EOS 70D camera. FPs were categorised into morphological type and the length (L) and width (W) were measured with imaging software, Image J (Rasband, 1997-2016). FP abundance (m-3) was calculated by dividing abundance per sample by the volume of the Niskin sampling bottle (12 L) and multiplying by 1000. The same calculation was used to calculate the volume and carbon of FPs (m-3).

Data quality:

To support identification, some items that were difficult to classify using the light microscope alone were extracted and analysed using scanning electron microscopy.