The unusual carbon biogeochemical cycling that occurred in the Ediacaran (ca. 635-541 Ma) ocean may have been critical for ocean oxygenation and Ediacaran life evolution. However, the triggers of the peculiar Ediacaran carbonate carbon isotope (delta C-13(carb)) excursions are not well understood. Because mercury (Hg) has a strong affinity for organic carbon, we measured Hg isotope compositions (delta Hg-202 and Delta Hg-199) from Ediacaran marine sediments of South China and South Australia to better understand the causes of the Ediacaran delta C-13(carb) excursions. During two local positive delta C-13(carb) excursions in the Doushantuo Formation, gradually decreasing Delta Hg-199 and increasing delta Hg-202 trends are primarily ascribed to enhanced terrestrial input. Decreasing delta Hg-202 in both the Doushantuo and Wonoka Formations during the latter part of the Shuram negative delta C-13(carb) excursion demonstrates the significant, and potentially widespread, contribution of upwelling Hg associated with dissolved organic carbon (Hg-DOC) from the open deep ocean. New Hg isotope data also suggest that a large Hg-DOC reservoir may have been present in the open ocean continuously from the early to mid-late Ediacaran Period (ca. 635-551 Ma), buffering ocean oxygenation at that time.