Persistent bottom water suboxic conditions caused by methane release events—Evidence from the South China Sea

Seepage of methane gas and/or oil across the seafloor is widespread at active and passive margins worldwide. Modern in situ observation shown that strongly reduced pH values and oxygen concentration in seep sediment pore water and local bottom waters, owing to the aerobic and/or anaerobic methane oxidation. However, questions remain about whether the suboxic conditions can widely develop in geological time, and the control factor for the occurrence of hypoxia remains largely unexplored. For two hydrocarbon seeps from the South China Sea, the pyrite sulfur isotope, and 16s rRNA sequence, as well as the redox-sensitive elements (Mo, U, Mn) are used to constrain the intensity of cold seep, and its impact on hypoxia. Our result show that the degree of hypoxia is related to the methane flux, and the bottom water suboxic conditions could stay for a relatively long period of time, on a scale of ten thousands of years. This study reveals the potential effect of seep activity on regulation bottom water oxygen concentration.

Acknowledgments:

Funding was provided by the NSF of China (Grants: 41672162).