Mercury Burial in Modern Sedimentary Systems of the East China Marginal Seas: The Role of Coastal Oceans in Global Mercury Cycling

Abstract

Coastal oceans, the transition zones between terrestrial and oceanic systems, are susceptible to anthropogenic mercury (Hg) inputs and are regarded as critical dynamic interfaces of the global Hg cycle. However, the extent to which coastal oceans are accountable for sequestering Hg remains largely unknown owing to the lack of data on high-resolution Hg accumulation in marine sediments. Synthesizing the results of this study (eight cores and 212 surface sediments) and the literature (three cores and 149 surface sediments), we provide a quantitative evaluation of the biogeochemical cycle of sedimentary Hg in the East China Marginal Seas (ECMS), including the response of the coastal marine sediments to anthropogenic disturbance as well as both human-derived and natural Hg burial fluxes. We find a linear increase in Hg accumulation since the 1950s (2.0 ± 2.5% yr⁻¹) and a decline in Hg accumulation between 2010 and 2016. Modern burial fluxes of total and anthropogenic Hg in the ECMS (covering ∼4.8 × 10⁵ km² of sea surface) were estimated to be 89.1 ± 48.3 and 35.9 ± 33.1 Mg yr⁻¹, respectively. Using a compilation of 688 surface sediments and 131 sediment cores (819 samples in total) distributed globally in coastal oceans, we estimate that approximately 1,590 (range: 1,190–2,760) Mg yr⁻¹ (Method 1) and 540 (range: 310–960) Mg yr⁻¹ (Method 2) Hg are accumulated in coastal ocean regions. Our findings suggest that coastal oceans are likely the largest global marine sinks for Hg and play a dominant role in regulating the oceanic Hg cycle and budgets.