Fig. 1

Site locations and 16S rRNA gene abundance. a Site locations are plotted on the map showing regions where dissolved oxygen and aerobic activity may occur throughout the sediment [3]. Circles and squares indicate marginal and open-ocean sites, respectively. Sediment samples were collected at different depths from the surface to 392 m below seafloor during 13 scientific drilling cruises from 38 drilling sites. In total, we analyzed 221 sediment samples. Leg 201, Ocean Drilling Program (ODP) Leg 201 Peru Deep Biosphere; Exp. 301, Integrated Ocean Drilling Program (IODP) Expedition 301 Juan de Fuca Hydrogeology; Exp. 307, IODP Expedition 307 Modern Carbonate Mounds: Porcupine Drilling; Exp. 308, IODP Expedition 308 Gulf of Mexico Hydrogeology; Exp. 315 and 316, IODP Expedition 315 and 316 NanTroSEIZE; Exp. 353, IODP Expedition 346 Asian Monsoon; Exp. 347, IODP Expedition 347 Baltic Sea Paleoenvironment; Exp. 353, IODP Expedition 353 Indian Monsoon Rainfall; Exp. 354, IODP Expedition 354 Bengal Fan; CK06-06, the Chikyu shakedown cruise offshore Shimokita; KN223, R/V Knorr cruise 223 in North Atlantic. b Depth distribution of prokaryotic 16S rRNA abundance quantified by microfluidic digital PCR (Supplementary Table S1). The red line indicates the regression line generated using least squares analysis with the abundance of 16S rRNA gene [log (16S rRNA gene abundance) = 7.03 − 0.97 log (depth), r² = 0.38]. The dashed black line shows the regression line [log (cell count) = 8.05 − 0.68 log (depth), r² = 0.70] of total direct cell count [10]. That regression line is based on cells per mL of sediment instead of copies per gram for dPCR