DNA extractions were successful to 10 cm below seafloor (cmbsf), at which the sediment temperature was ∼60°C (Fig. 1A). Sulfate concentrations decreased steeply in the upper cmbsf and were below the detection limit (∼0.1 mM) below a 4-cm depth, indicating active sulfate reduction within the surface layers and sulfate limitation below (Fig. 1B). The absence of sulfate in the deeper sediment layers indicates minimal core disturbance and seawater in-mixing during sampling and retrieval.