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Human activity is influencing the global osmium cycle, driving the Os isotopic composition ( 187 Os/ 188 Os) of the hydrosphere and associated sedimentary material to lower values. Here, we present the Re and Os abundance and isotope systematics of macroalgae, a proxy for seawater, from Tokyo Bay to elucidate the potential sources of anthropogenic Os to the Pacific Ocean. Macroalgae from the Uraga Channel, which connects Tokyo Bay to the Pacific Ocean, record relatively low Os abundances (∼10.1 pg/g) and an 187 Os/ 188 Os of ∼0.9, indicative of surface ocean seawater. Contrastingly, macroalgae within the bay closest to central Tokyo record the highest Os abundances (∼22.8 pg/g) and lowest 187 Os/ 188 Os values (∼0.47), suggesting contamination from human activity. To determine the source of anthropogenic Os, we have developed the first Os emission inventory, based on the East Asian Air Pollutant Emission Grid database (EAGrid2010). The close relationship ( R 2 = 0.67 and p -value = <0.05) between Os inventories and macroalgal data suggests that municipal solid waste incinerators (MSWIs) are the dominant source of Os to Tokyo Bay. Projections for Japan estimate that 26 -18 +38 ng Os/m 2 /yr is released from MSWI smokestacks, leading to a concentration in precipitation of 26 -18 +38 fg/g, identifying MSWIs as a major contributor of anthropogenic Os to the hydrological cycle.

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.