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.

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Elemental carbon (EC), the highly recalcitrant carbonaceous material released exclusively from fossil fuel combustion and biomass burning, is a preferred geochemical agent for evaluating anthropogenic activities. We investigated the spatiotemporal trends of EC and char/soot ratios (char and soot, the two subtypes of EC, differ in formation mechanisms and physicochemical characteristics) in five sediment cores from eastern China marginal seas, spatially spanning from inshore coastal mud areas to offshore remote mud areas. The temporal profiles of EC depositional fluxes closely tracked socioeconomic development in China over the past ∼150 years, with the most pronounced increasing trend beginning in the early 1980s, commensurate with the implementation of national policy of Reform and Open in 1978. The temporal EC profiles in China differed significantly from those in European/American countries, reflecting their different socioeconomic development stages. The spatiotemporal trends of char/soot ratios were also highly informative. Temporally, they decreased from bottom to subsurface layers, indicating the switch of China from an agricultural economy to an industrial economy during the 20th century. Spatially, they decreased from inshore to offshore areas, suggesting the differential transport patterns of EC among these sampling regimes.

Elaborating the spatiotemporal variations and dynamic mechanisms of black carbon (BC) in coastal seas, the geographically pivotal intermediate zones that link the terrestrial and open oceanic ecosystems, will contribute significantly to refine the regional and global BC geochemistry. In this study, we implemented a large spatial-scale and multiseason and -layer seawater sampling campaign in high BC emission influenced coastal China seas (Bohai Sea and Northern Yellow Sea) and quantified the thermal/optical reflectance-based particulate BC (PBC) and benzene polycarboxylic acids-based dissolved BC (DBC). We found that the climate and its associated hydrological effects (including the intensive resuspension and coastal current transport) largely regulate both PBC and DBC spatiotemporal variations and dynamics. In combination with previous work on upstream rivers and downstream open ocean, a significant and continuous decrease in the DBC aromatic condensation was observed along the river-to-ocean continuum, probably due to the increment of the photochemical degradation during the waterborne transport. Based on our DBC methodological development, i.e., the determination and subsequent inclusion of the nitrated BC molecular markers, the magnitudes of the current global DBC fluxes and pools were updated. After the update, the DBC fluxes from atmospheric deposition and riverine delivery were estimated at rates of 4.3 and 66.3 Tg yr −1 , respectively, and the global oceanic DBC pool was approximately 36 Gt. This update will greatly assist in constructing a more robust regional and global DBC and BC cycling and budgets.

Black carbon is ubiquitous in the marine environment. However, whether it accumulates in the deepest ocean region, the hadal zone, is unknown. Here we measure the concentration and carbon isotopes (δ13C and Δ14C) of black carbon and total organic carbon in sediments from six hadal trenches. Black carbon constituted 10% of trench total organic carbon, and its δ13C and Δ14C were more negative than those of total organic carbon, suggesting that the black carbon was predominantly derived from terrestrial C3 plants and fossil fuels. The contribution of fossil carbon to the black carbon pool was spatially heterogeneous, which could be related to differences in the distance to landmass, land cover and socioeconomic development. Globally, we estimate a black carbon burial rate of 1.0 ± 0.5 Tg yr−1 in the hadal zone, which is seven-fold higher than the global ocean average per unit area. We propose that the hadal zone is an important, but overlooked, sink of black carbon in the ocean.

Black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) are byproducts generated from the incomplete combustion of organic materials, including fossil fuels and biomass. The similar production processes shared by BC and PAHs provide the possibility to infer the BC sources using the PAHs signatures. This study successfully utilized data sets of BC and PAHs analyzed from the continental shelf surface sediments of the Bohai and Yellow Seas to a standard receptor model of positive matrix factorization (PMF) to apportion the sources of BC in the sediment matrix. Results showed that combustion of fossil fuels (i.e., coal and oil/petroleum) accounted for an average level of 83 ± 5% of the total BC preserved, which was significantly higher than that from the biomass burning (17 ± 5%). The spatial distributions of the fossil BC concentrations and percentages differed significantly from those of the biomass BC, implying their different geochemical behaviors in the continental shelf regimes and further emphasizing the importance to effectively differentiate between fossil BC and biomass BC. In addition to the relative proportions of the BC subtypes (char‐BC/soot‐BC), the regional‐specific hydrodynamic conditions, including the cold cyclonic eddy, resuspension and coastal current, also exerted a significant influence on these spatial variations.

• PM 2.5 and TSP samples collected at Yellow River Delta were analyzed for OC and EC.• OC, EC, TSP and PM 2.5 concentrations were higher in daytime than in nighttime.• Radiocarbon ( 14 C) tracer, backward trajectories, and fire counts were used for the analysis.• Agricultural waste open burning was a main contributor to summer PM 2.5 , OC and EC. a b s t r a c t a r t i c l e i n f o Samples of total suspended particulates (TSPs) and fine particulate matter (PM 2.5 ) were collected from 29th May to 1st July, 2013 at a regional background site in Bohai Rim, North China. Mass concentrations of particulate matter and carbonaceous species showed a total of 50% and 97% of the measured TSP and PM 2.5 levels exceeded the first grade national standard of China, respectively. Daily concentrations of organic carbon (OC) and elemental carbon (EC) were detected 7.3 and 2.5 μg m −3 in TSP and 5.2 and 2.0 μg m −3 in PM 2.5 , which accounted 5.8% and 2.0% of TSP while 5.6% and 2.2% for PM 2.5 , respectively. The concentrations of OC, EC, TSP and PM 2.5 were observed higher in the day time than those in the night time. The observations were associated with the emission variations from anthropogenic activities. Two merged samples representing from south and north source areas were selected for radiocarbon analysis. The radiocarbon measurements showed 74% of water-insoluble OC (WINSOC) and 59% of EC in PM 2.5 derived from biomass burning and biogenic sources when the air masses were from south region, and 63% and 48% for the air masses from north, respectively. Combined with backward trajectories and daily burned area, open burning of agricultural wastes was found to be predominating, which was confirmed by the potential source contribution function (PSCF).