Oxygen Minimum Zone and Organic Carbon Structure Benthic Prokaryotic Communities and Metabolism in Warm Deep-Red Sea Sediments

Benthic prokaryotic communities in deep-sea sediments remain poorly studied. They are constrained by organic matter availability and oxygenation in warm deep-sea ecosystems. Here, we investigated benthic prokaryotic communities and carbon uptake in deep Red Sea sediments (218–2415 m seafloor depth), where persistently warm (~21.5 °C) waters and a strong south–north productivity gradient co-occur. Sediment particulate organic carbon (POC), prokaryotic abundance (PA), and [13C]-D-glucose-based carbon uptake and uptake kinetics were examined in two sediment layers (0–1 and 4–5 cm), while bacterial communities were characterized using 16S rRNA gene sequencing of the 0–1 cm layer. Sediment POC, PA, and carbon uptake declined northward, consistent with reduced organic-carbon supply to the seafloor. Bacterial community composition differed significantly across the ~500 m depth associated with the Red Sea oxygen minimum zone (OMZ). Sediments from the relatively low-oxygen upper OMZ-range (200–500 m) had higher sediment POC and PA, and were enriched in putatively anaerobe-associated taxa, whereas deeper sediments (>500 m) below the OMZ exhibited more fragmented co-occurrence networks. These results suggest that organic-carbon availability defines the basin-scale metabolic backdrop, whereas bacterial community differentiation was more clearly resolved between upper OMZ-range and below-OMZ sediments than along latitude alone.