Spatio-temporal distribution of carbon in the Bohai Sea sediments under high human perturbations

The Bohai Sea is one of marginal seas in the world, which suffers from strong human perturbations. This study collected sediment cores from four stations across the Yellow River estuary to the central Bohai Sea. The profiles of sediment organic and inorganic carbon contents as well as their δ 13 C values combined with porewater geochemical parameters (dissolved inorganic carbon (DIC), Fe 2+ , SO 4 2− , NH 4 + ) were analyzed to explore the spatio-temporal distribution of carbon and the controlling processes. The results show that the total organic carbon (TOC) contents are from 0.3 to 1.4 % and the contribution of terrestrial carbon is highest in the Yellow River estuary ranging from 54.11 to 95.09 %, with an average of 71.34 %, while it is lower in central Bohai Sea varying from 39.75 to 78.83 %, with an average of 50.60 %. The total inorganic carbon (TIC) contents in the central Bohai Sea are from 0.33 to 0.63 %, which is much lower than that in the Yellow River estuary with a range of 1.26–1.96 %, suggesting the large influence of riverine inputs. Variations of porewater geochemical parameters in the top meter sediments reflect both iron oxide reduction dominated early diagenetic processes and ongoing regulations on the Yellow River in the past decades, including the re-direction of the Yellow River mouth and the sediment-water regulation scheme. We also estimate a DIC efflux from the Bohai Sediments, 0.16 Tg C/yr, which is up to 10 % of the DIC inputs of the Yellow River. This implies an important role of the sediments in maintaining alkalinity and ocean chemistry in the Bohai Sea.