Objectives: Recent studies have provided the first evidence for the simultaneous microbial production and consumption of methane in the sulfate reduction zone of organic-rich sediments, a process named the "cryptic methane cycle." In this process, methane is proposed to be passed directly from methylotrophic methanogenesis to anaerobic oxidation of methane (AOM). However, little is known about the identity of the organisms involved, the trail of carbon from one metabolism to the other, or the environmental net result of the two processes. Our study will focus on sediments from the Carpinteria Salt Marsh Reserve, a productive coastal wetland in Southern California. We will apply radioisotope and stable isotope labeling of collected sediments and combine these methods with molecular probing and nanoscale secondary iron mass spectrometry to investigate cryptic methane cycling on the microbial level. Field measurements of methane emission rates and biogeochemical profiles of sediments along the salinity gradient of the salt marsh will provide information on factors that control cryptic methane cycling and methane release into the atmosphere. As a research assistant, I am involved in collecting sample from the field, slicing sediment cores, preparing media, culturing bacteria and archaea, running ion chromatography, etc.