Flux and budget of BC in the continental shelf seas adjacent to Chinese high BC emission source regions

This study conducted the first comprehensive investigation of sedimentary black carbon (BC) concentration, flux, and budget in the continental shelves of "Bohai Sea (BS) and Yellow Sea (YS)," based on measurements of BC in 191 surface sediments, 36 riverine water, and 2 seawater samples, as well as the reported data set of the atmospheric samples from seven coastal cities in the Bohai Rim. BC concentrations in these matrices were measured using the method of thermal/optical reflectance. The spatial distribution of the BC concentration in surface sediments was largely influenced by the regional hydrodynamic conditions, with high values mainly occurring in the central mud areas where fine-grained particles (median diameters>6 Φ (i.e., <0.0156mm)) were deposited. The BC burial flux in the BS and YS ranged from 4 to 1100μg/cm²yr, and averaged 166±200μg/cm²yr, which was within the range of burial fluxes reported in other continental shelf regimes. The area-integrated sedimentary BC sink flux in the entire BS and YS was ~325Gg/yr, and the BS alone contributed ~50% (~157Gg/yr). The BC budget calculated in the BS showed that atmospheric deposition, riverine discharge, and import from the Northern Yellow Sea (NYS) each contributed ~51%, ~47%, and ~2%. Therefore, atmospheric deposition and riverine discharge dominated the total BC influx (~98%). Sequestration to bottom sediments was the major BC output pattern, accounting for ~88% of the input BC. Water exchange between the BS and the NYS was also an important BC transport route, with net BC transport from the BS to the NYS.