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.
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