Particulate and Dissolved Black Carbon in Coastal China Seas: Spatiotemporal Variations, Dynamics, and Potential Implications

Abstract

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.

Particulate and Dissolved Black Carbon in Bohai and Laizhou Bays, China: Distributions, Sources, and Contrasts Under Two Distinct Fluvial Hydrological Regimes

“…Coastal seas, including coastal bays, are the geographically critical transitional zone that links terrestrial and open oceanic ecosystems (Bauer et al, 2013;Fang et al, 2018a;Fang et al, 2021). Despite comprising only 7-10% of global ocean surface area, the coastal seas are responsible for 20-30% of global marine primary productivity and up to 80-90% of organic carbon (OC) accumulation in marine sediments (Bauer et al, 2013;Keil, 2017;Fang et al, 2018a).…”

“…Soil BC is mobilized to adjacent rivers and then to coastal seas through wind, erosion, and/or leaching pathways (Abney and Berhe, 2018;Coppola et al, 2018), supplying a continuous contribution of fire-derived carbon to the aquatic environments (Wagner et al, 2018). In the natural water bodies, BC occurs simultaneously as particulate and dissolved phases (i.e., PBC and DBC) (Wagner et al, 2015;Wang et al, 2016;Xu et al, 2016;Myers-Pigg et al, 2017;Fang et al, 2018a;Wagner et al, 2018;Qi et al, 2020;Fang et al, 2021;Liu and Han, 2021). Available studies regarding process-based BC fluxes suggested that global rivers deliver 17-37 and 18-66 Tg-C yr −1 of PBC and DBC to the coastal seas, respectively (Jaffé et al, 2013;Coppola et al, 2018;Jones et al, 2020;Fang et al, 2021).…”

“…In the natural water bodies, BC occurs simultaneously as particulate and dissolved phases (i.e., PBC and DBC) (Wagner et al, 2015;Wang et al, 2016;Xu et al, 2016;Myers-Pigg et al, 2017;Fang et al, 2018a;Wagner et al, 2018;Qi et al, 2020;Fang et al, 2021;Liu and Han, 2021). Available studies regarding process-based BC fluxes suggested that global rivers deliver 17-37 and 18-66 Tg-C yr −1 of PBC and DBC to the coastal seas, respectively (Jaffé et al, 2013;Coppola et al, 2018;Jones et al, 2020;Fang et al, 2021). It is therefore of great necessity and importance to elaborate the distributions and sources of BC in coastal seas, especially those areas strongly influenced by high intensity of BC emission (Wang et al, 2012;Wang et al, 2014), such as the eastern China marginal seas, which will largely refine the regional and even global BC cycle (Fang et al, 2018a;Fang et al, 2021).…”

“…Though comprising only 5% of the Chinese territory, these areas contribute >20% of China's total BC emission. Under the integrated impacts from large amounts of riverine discharge (including the Yellow River (Figure 1B), carrying the world's second largest sediment loads into the ocean (Hu et al, 2016)) and prevailing northerly/northwesterly winter and spring East Asian monsoon, large quantities of BC produced in Bohai Rim can be easily migrated to the adjacent coastal Bohai Sea and then involved in the coastal carbon cycle (Wang et al, 2016;Xu et al, 2016;Fang et al, 2015;Fang et al, 2018a;Fang et al, 2021). This renders the coastal Bohai Sea as an important BC reservoir (Huang et al, 2016;Fang et al, 2015;Fang et al, 2018a;Fang et al, 2021).…”

“…To date, there have been plenty of investigations concerning PBC on the regional atmosphere, soils, sediments, and coastal wetlands in Bohai Rim (Li and Bai, 2009;Liu et al, 2011;Chen et al, 2013;Huang et al, 2014;Andersson et al, 2015;Fang et al, 2015;Zhang et al, 2015;Fang et al, 2016;Liu et al, 2016;Xu et al, 2017;Fang et al, 2018b;Shao et al, 2018). In comparison, however, the available studies draw relatively less attention on PBC in the aquatic environments (such as the riverine water and coastal seawater), let alone the analytically highly complicated and challengeable DBC (Wang et al, 2016;Xu et al, 2016;Fang et al, 2018a;Qi et al, 2020;Fang et al, 2021). The relative absence of refined studies on PBC and DBC in aquatic ecosystems might to a large extent hamper our comprehensive understanding of BC geochemistry in this high-intensity BC emission affected coastal zones.…”