Rivers as the largest source of mercury to coastal oceans worldwide

Mercury evidence for combustion of organic-rich sediments during the end-Triassic crisis

“…For this reason, terrestrial materials (e.g., vegetation and soil) are commonly characterized by elevated Hg concentrations 44 and negative Δ 199 Hg values (e.g., ranging from −0.4‰ to 0‰ 35,36,45 . Furthermore, negative Δ 199 Hg values have been observed in coastal sediments that receive Hg mainly via terrestrial runoff 16,32 . Mercury has a close association with organic matter in organic-rich sediments, and decay of organic compounds can result in release of soil Hg to the atmosphere 13 .…”

“…The excess Hg at Katsuyama was almost certainly sourced from the atmosphere given the distance of this pelagic section from continents (i.e., several thousand kilometers). Although warm and humid climate conditions may have increased Hg weathering fluxes, most river-borne detrital materials are deposited on continental shelves, within ~100 km of river mouths 31 , 32 . In addition to distance, a terrestrial Hg source is rendered unlikely due to lack of a significant correlation between Hg and Th (Supplementary Fig.…”

“…In addition to distance, a terrestrial Hg source is rendered unlikely due to lack of a significant correlation between Hg and Th (Supplementary Fig. 1 ), and to the relatively short residence time of Hg in seawater (10 1 –10 2 years 33 ), limiting its redistribution within the ocean system 32 (Supplementary Note 1 ). Furthermore, multiple Hg peaks near the extinction interval in the present study section and at correlative sites 14 , 17 – 19 document that the CAMP eruptions were likely to have been pulsed, an inference supported by U-Pb dating 1 , 2 .…”

“…1 ). Terrestrial inputs of eroded soil through rivers are unlikely to have played a significant role given the thousands of kilometers separating Katsuyama from continental sources as well as the lack of correlations between Hg and Th 32 . We infer that heating of soil and terrestrial biomass (e.g., vegetation) through wildfires and/or contact metamorphism of organic-rich sedimentary rocks by igneous sills was the main source of low-MIF Hg.…”

Concentrations and Yields of Total Hg and MeHg in Large Boreal Rivers Linked to Water and Wetland Coverage in the Watersheds

“…Knowing that the Eastern portion accounts for around 50% of the area of the whole James Bay watershed, this suggests that either the Western James Bay may have higher yields than the Eastern side, or that the model of Liu et al. (2021) tends to overestimate Hg yields in this boreal region. Nonetheless, the fluxes calculated in our study provide an essential empirical estimate to assess overall fluxes to the bay.…”