A Cryptic Sulfur Cycle in Oxygen-Minimum–Zone Waters off the Chilean Coast.

Nitrogen cycling is normally thought to dominate the biogeochemistry and microbial ecologyof oxygen-minimum zones in marine environments. Through a combination of moleculartechniques and process rate measurements, we showed that both sulfate reduction and sulfideoxidation contribute to energy flux and elemental cycling in oxygen-free waters off the coast ofnorthern Chile. These processes may have been overlooked because in nature, the sulfide producedby sulfate reduction immediately oxidizes back to sulfate. This cryptic sulfur cycle is linked toanammox and other nitrogen cycling processes, suggesting that it may influence biogeochemicalcycling in the global ocean.