Holocene climate regulates multiple sulfur isotope compositions of pyrite in the East China sea via sedimentation rate

Marine authigenic pyrite sulfur isotope (delta S-34(pyr)) is one of the most important proxies for reconstructing remarkable changes of Earth's surface in deep time. Recent observations of unexpectedly large delta S-34(pyr) variations in Quaternary sediments complicate the application of this isotopic proxy, and a mechanistic understanding of such variabilities is needed. In this study, we measured multiple sulfur isotopic compositions of pyrite in well dated sediments spanning the last 7500 years from the East China Sea (ECS) inner shelf to study the mechanism how Holocene climate controls pyrite sulfur isotopic compositions. We found that variabilities of pyrite multiple sulfur isotopes, delta S-34(pyr) and Delta S-33(pyr) (ranging from -38.3 parts per thousand to 2.3 parts per thousand and from -0.01 parts per thousand to 0.21 parts per thousand, respectively) are significantly correlated with large fluctuations of sedimentation rates (0.03-2.09 cm/yr). In tandem with box model calculations and compiled data, the large delta S-34(pyr) variations up to 40 parts per thousand are primarily ascribed to fluctuated anaerobic oxidation of methane coupled sulfate reduction (AOM-SR). Further analyses suggest that heightened distillation of interstitial sulfate, likely propelled by high methane flux coupled with increased sedimentation rates, can produce such negatively correlated delta S-34(pyr)-Delta S-33(pyr) pattern and large variations in delta S-34(pyr). Possible changes in isotope fractionation factors caused by varied cell-specific sulfate reduction rates result in a maximum delta S-34(pyr) variation of <20 parts per thousand and therefore play a minor role in the large variation in delta S-34(pyr) (>40 parts per thousand). The major and minor isotopic compositions of pyrite align with sulfide produced through pure sulfate reduction, indicating little evidence of additional oxidative sulfur cycling. Sedimentation rates in the ECS are controlled by the East Asian winter monsoon that influences the sediment transport capacity from longshore currents on a multicentennial timescale, and also by the coupled East Asian summer monsoon that affects the sediment availability from the Yangtze River on a millennial timescale. Holocene climate changes alter sediment supplies at the ECS and therefore play a vital role in controlling multiple sulfur isotope compositions of sedimentary pyrite in this region. This study has the potential to provide new insights into delta S-34 excursions in seawater sulfate that occurred during periods of notable acceleration in sedimentation rates throughout the geological history.