Global maps of sulfate and methane in marine sediments reveal two provinces of subsurface metabolic activity: a sulfate-rich open-ocean province, and an ocean-margin province where sulfate is limited to shallow sediments. Methane is produced in both regions but is abundant only in sulfate-depleted sediments. Metabolic activity is greatest in narrow zones of sulfate-reducing methane oxidation along ocean margins. The metabolic rates of subseafloor life are orders of magnitude lower than those of life on Earth's surface. Most microorganisms in subseafloor sediments are either inactive or adapted for extraordinarily low metabolic activity.

The sediment depth gives the base of SO42- reduction zone in mbsf. Where no depth is given SO42- is present throughout the drilled hole and, consequently, that there is no base to the SO4**-2 reduction zone in the sampled sediment column.

Supplement to: DHondt, Steven; Rutherford, Scott D; Spivack, Arthur J (2002): Metabolic activity of subsurface life in deep-sea sediments. Science, 295(5562), 2067-2070