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., <0.0156 mm)) were deposited. The BC burial flux in the BS and YS ranged from 4 to 1100 μg/cm 2 yr, and averaged 166 ± 200 μg/cm 2 yr, 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~325 Gg/yr, and the BS alone contributed~50% (~157 Gg/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.

Organic carbon (OC) cycling in coastal seas that connect terrestrial and open oceanic ecosystems is a dynamic and disproportionately important component of oceanic and global carbon cycles. However, OC cycling in coastal seas needs to be better constrained, particularly for geochemically important black carbon (BC). In this study, we conducted multimedium sampling campaigns, including atmospheric deposition, river water, seawater, and sediments in coastal Bohai Sea (BS) in China. We simultaneously quantified particulate OC (POC), particulate BC (PBC), dissolved OC (DOC), and dissolved BC (DBC) and investigated the cycling and budgets of OC and BC. The cycling and budgets of each individual particulate phase (i.e., POC versus PBC) and dissolved phase (i.e., DOC versus DBC) displayed similar patterns, but there were some distinct differences between the particulate and dissolved phases. In the particulate phases, atmospheric and riverine delivery dominated exogenous inputs (>80%), sequestration to sediments dominated removal (~70%), and exchanges in the Bohai Strait resulted in net export. In the dissolved phases, exchanges in the Bohai Strait dominated both import and export and were in a relatively dynamic equilibrium. We found that both natural perturbations, such as spring dust storms, and anthropogenic activity, exerted significant impacts on BS carbon cycling. The integration of regional and global source‐to‐sink process databases made it clear that future BC studies should calculate PBC and DBC fluxes independently. Continuous field observational studies, more details of the biogeochemical processes involved, and consistent BC quantification methods are urgently needed to elucidate coastal OC and BC cycling.