Microbial sulfate reduction and organic sulfur formation in sinking marine particles.

Climate change is driving an expansion of marine Oxygen Deficient Zones, which may alter the global cycles of carbon, sulfur, nitrogen, and trace metals. Currently, however, we lack a full mechanistic understanding of how oxygen deficiency affects organic carbon cycling and burial. Here, we show that 'cryptic' microbial sulfate reduction occurs within sinking particles from the Eastern Tropical North Pacific Oxygen Deficient Zone, and that some microbially-produced sulfide reacts rapidly to form organic S that is resistant to acid hydrolysis. Particle-hosted sulfurization could enhance carbon preservation in sediments underlying O2 -deficient water columns and serve as a stabilizing feedback between expanding anoxic zones and atmospheric CO2 A similar mechanism may help explain more extreme instances of organic carbon preservation associated with marine anoxia in Earth history.