Methodology:

Data were collected from each of 5 stations in 2017 (B13-B17) and 6 stations in 2018 (B13-B17 and Xs) during two consecutive cruises (RRS James Clark Ross: JR16006, 30th June to 8th August, 2017; JR17007: 10th July to 5th August, 2018) following a transect along the 30ºE meridian. At each station four replicate intact sediment cores (LWH: 20 x 20 x 12 cm) were obtained from replicate 0.1m2 USNL (Unites States Naval Laboratory) box cores using a core extruder, transferred to transparent acrylic aquaria (internal dimensions, LWH: 20 x 20 x 34 cm) and overlain with ~8 L (20cm depth) surface seawater (salinity, ~34). Aquaria (2017, n = 20; 2018, n = 24) were randomly transferred to one of two insulated fibreglass seawater baths (LWH: 1.2 x 1.2 x 0.8m, Tanks Direct, UK) and maintained at a representative ambient bottom temperature in the dark. Faunal mediated sediment particle reworking metrics were estimated after 12 days by establishing the redistribution of optically distinct particulate tracers (luminophores: 215g aquaria-1, fluorescent green, <200µm silica sand, density 2.35 kg dm-3; Glass Pebbles Ltd., UK). The ventilatory behavior of the infauna (bioirrigation) was estimated from absolute changes in the concentration (10mM, 8.231g NaBr dissolved in seawater aquarium-1) of the inert tracer sodium bromide (Delta [Br-], mg L-1; negative values indicate increased infaunal ventilatory activity) over an 8 h period on day 12, determined using a Tecator flow injection auto-analyser (FIA Star 5010 series). Accumulated water column concentrations (µmol L-1) of NH4-N, NOx-N (i.e. NO3-N + NO2-N) and PO4-P were determined after 12 days incubation from standardized samples (taken from the centre of each aquarium at ~5cm depth, 0.45 µm NALGENE filtered) following standard protocols using a Lachat Quikchem 8500 flow-injection auto-analyser. Full descriptions and additional information provided in Solan et al. 2020 Phil. Trans. R. Soc. A. in main manuscript and supplementary information.

Resolution:

Particle redistribution resolution 83 µm in 2017 and 74 µm in 2018.

Nutrient concentrations to two decimal places

Data collection:

Instrumentation:

Canon 400D digital SLR camera

Tecator flow injection auto-analyser (FIA Star 5010 series)

Lachat Quikchem 8500 flow-injection auto-analyser

Data quality:

Standard protocols were followed and data entry double checked by independent person.