Significance Mercury is a globally ubiquitous pollutant that is harmful to humans and animals. Most mercury entering the environment is released from anthropogenic sources and then stored for some period in soils and water bodies before potentially being remobilized, which greatly facilitates its global distribution. Although the ocean is recognized as the largest ultimate sink of mercury, the distribution and burial of mercury in deep ocean sediments remains largely unknown because of the difficulty in obtaining samples from these ecosystems. This study found that although hadal trenches (the deepest parts of the oceans) occupy a very small portion (<0.5%) of the ocean area, they may receive a large amount of mercury and represent a disproportionately important, previously overlooked sink for mercury.