Blue carbon ecosystems such as seagrass meadows, mangrove forests, and salt marshes are important carbon sinks that can store carbon for millennia. Recently, organic matter sulfurization and pyritization have been proposed as mechanisms of net carbon storage in blue carbon ecosystems. At our study site, organic sulfur that is resistant to acid hydrolysis (protokerogen) is an order of magnitude less abundant than pyrite sulfur,...

Organic sulfur plays a crucial role in the biogeochemistry of aquatic sediments, especially in low sulfate ( μ M) environments like freshwater lakes and the Earth's early oceans. To better understand organic sulfur cycling in these systems, we followed organic sulfur in the sulfate‐poor ( μ M) iron‐rich (30–80 μ M) sediments of Lake Superior from source to sink. We identified microbial populations with shotgun metagenomic sequ...