Geochemistry and mineralogy coupling reveals the Fe-S cycle in a receding methane seep (Supplementary data)

Receding methane seep is a potential hotspot to investigate the iron and sulfur cycle in marine sediment but these processes deciphered by geochemical and mineralogical data are still unclear. Here, we studied a core with a length of 14 m sampled from the Shenhu area, South China Sea, via multiple geochemical and mineralogical methods, we found twice methane seep activities. Accelerator mass spectrometry 14C dating and the carbon and oxygen isotopic analyses for planktonic foraminifera indicate successive sedimentation from Marine isotope stages 3 (MIS3) to 1 (MIS1). The low correlations between CRS and total organic carbon (TOC) and δ13CTOC indicate that organoclastic sulfate reduction is not the dominant biogeochemical reaction in this core. The increasing contents of CRS and the mean diameter of framboid in several depth intervals and the extremely negative δ34S value of both CRS and hand-picked pyrite reveal that the two SMTZs once situated near the seafloor. The vast ES and framboid goethite (pyrite pseudomorphs) that distribute throughout the core implied that the methane seep activity had subsided. Moreover, the special intermediate species further confirmed the ongoing pyrite oxidation. Therefore, our results provide a unique reference to interpret the Fe-S cycle in methane seep.