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

Abstract

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.

Distribution, input pathway and mass inventory of black carbon in sediments of the Gulf of Thailand, SE Asia

“…Therefore, it is worth noting that the direct comparison as noted above was complicated considering the used different BC quantification methods with regard to the BC sources and sinks. Anyway, based on the same BC measurement procedures, the mass inventory of BC in the GOT in the present study was comparable with our recent work in the Bohai Sea (~147 Gg/y) and the Yellow Sea (~171 Gg/y) off the western Pacific margins (Fang et al, 2015). The semi-enclosed Bohai Sea and Yellow Sea, from the moderatehigh latitude region, are mainly situated at the downwind area of the East Asian Monsoon, receiving large amounts of combustionderived substances (e.g., PAHs) through atmospheric deposition, especially in the winter season due to the extensive regional heating activities in China (Wang et al, 2014).…”

“…The blank samples (n ¼ 10) yielded 0.00 ± 0.00 mg/cm 2 for BC, and the RSD of 10 pairs of replicate analyses was in the range of 0e11%, and averaged within 5%. The BC concentration measured in SRM 1941b was 10.56 ± 1.28 mg/g (n ¼ 10), which was well in accordance with the values reported by recent studies (Hammes et al, 2007;Han et al, 2007a;Cong et al, 2013;Fang et al, 2015). These QA/QC results suggested that the BC analytical method used here was credible and repeatable (see Supplementary materials).…”

“…In the present work, the wet-chemical treatment combined with thermal/optical reflectance (TOR) detection was adopted (Han et al, 2007a(Han et al, , 2007bFang et al, 2015). Briefly, the thawed, freeze-dried and homogenized (<80 meshes) sediment samples were treated with hydrochloric and hydrofluoric acids to remove inorganic materials.…”

“…(Han et al, 2007b(Han et al, , 2015a. Detailed procedures for the BC separation and quantification are available in our recent work (Fang et al, 2015).…”

“…For quality assurance and quality control (QA/QC), whether the residue on the filters has an even distribution is a primary factor that markedly influences the accuracy of the BC concentration determination (Khan et al, 2009;Han et al, 2011;Fang et al, 2015). The typical filters loaded with acid-treated sediment residue are displayed in Fig.…”