A Century-old Historical Variation In Black Carbon Deposition To The Japan Sea Sediments

Black carbon has a small particles size,thus can be transported over long distance through water bodies and the atmosphere.Along all of its sink,marine sediments are generally considered to be the final sink of black carbon storage.In addition,black carbon has a highly aromatic structure,resulting in high stability and long-term preservation in sediments.Owning to the two reasons above,marine sediments are selected as the medium to study the historical variation of black carbon.The Japan Sea is the largest marginal sea in the northwest Pacific and is located in the downwind of the Eurasian continent.Therefore,studying the historical variation in black carbon of the Japan Sea sediments is of great significance for understanding the pollution emissions of the Eurasian continent.In this study,we collected four sediment cores from the Japan Sea:core LV53-4-1,which is located in the northern Japan Sea and near the Tatar Strait;core LV53-15-3 and LV53-17-2,which are located in the western Japan Sea;core LV53-19-3,which is located in the Yamato Ridge.In all four sediment cores,210Pbex has a good correlation with the depth and the grain size composition is stable,indicating that the deposition environment is stable and suitable for the study of historical variation of black carbon.Black carbon concentration of the four cores are 1.07±0.29 mg g-1 0.52 ± 0.13 mg g-1,0.99±0.20 mg g-1,1.13±0.16 mg g-1,respectively.Black carbon fluxes of the four cores are 2.56 ± 0.70 g m-2 yr-1,1.31 ± 0.32 g m-2 yr-1,2.42±0.69 g m-2 yr-1,1.35 ±0.19 g m-2 yr-1,respectively.And they are comparable with other studies.There is a significant negative correlation between black carbon concentration and sand content,and a significant positive correlation with clay content.There is a significant positive correlation between black carbon concentration and total carbon concentration,indicating that black carbon and total organic carbon are likely to deposit simultaneously.Black carbon fluxes are 5-10 times of that in the Tibet Plateau.Core LV53-4-1,influenced by riverine discharge from the Amur River and atmospheric transport from Russia,witnessed increasing trends and then decreasing trends from the 1980s to the early of the 21st century,peaked in 1990.Core LV53-15-3,mainly affected by the atmospheric transport from Russia and the borders of Russia and China,showed decreasing trends and then increasing trends from the 1990s to the early of the 21st century,reached a minimum in 2000.Core LV53-17-2 and LV53-19-3,mainly affected by atmospheric transport from China,were consistent with social and economic development,especially in the 1980s and the early 21st century,due to the implementation of Reform and Open policy and expanding of industrialization and urbanization,the black carbon fluxes rose drastically.The lowest value of Char/Soot in the core LV53-19-3 appeared in the 1980s,indicating that China's energy structure has changed from the agricultural economy to the industrial economy.Black carbon in sediments has strong absorption to organic matter such as PAHs and PCBs.The BC/TOC ratios are used to evaluate the ecological effects of black carbon in the sediments.BC/TOC ratios of the four sediment cores were 10±2.28%,7±0.83%,10±2.03%and 19±1.79%,respectively.Based on the previous studies,we find that black carbon absorption is the main mode of organic matter absorption in sediments and black carbon can reduce the enrichment of PAHs in living organisms.These two mechanisms reduce the exposure of organic matter to the aqueous environment and the enrichment in the living organisms,indicating the presence of black carbon can improve and repair the sedimentary environment to some extent.Comparing the simulation results of the nine models of CMIP5 and observation results,it is found that the climate model significantly underestimate the black carbon fluxes in the study area.The observation results in the Japan Sea are 50-100 times to the simulation results,indicating the removal mechanism(dry and wet deposition)of black carbon from the climate model has yet to be optimized.Via the relative root mean square error method and EOF analysis method,the climate model simulation results are evaluated in two dimensions of space and time.It is found that model ACCESS 1-0 has the best simulation on the temporal trends of black carbon fluxes,while model MIRO-ESM-CHEM has the best simulation on the spatial distribution of black carbon fluxes.Overall,the atmospheric black carbon fluxes in the Japan Sea decreases with increasing latitude,and the inconsistency of core LV53-4-1 further indicates that this core is affected by both riverine discharge and atmospheric transport.