Sources and preservation of sedimentary organic matter in the Southern Bohai Sea and the Yellow Sea: Evidence from lipid biomarkers

Abstract

a b s t r a c tThe region of Southern Bohai Sea (SBS) and Yellow Sea (YS) represents one of the best examples of large river-dominated ocean margins. The transport and accumulation of sediments played a primary role in distribution of the lipids in the region and could lead to a preferential accumulation of these more refractory land-based lipids. The spatial distribution of total organic carbon (TOC) matched with the lipid distributions over the shelf, and high TOC presented in the central YS, but TOC burial fluxes decreased from 110 ton/km 2 /yr of SBS to 25-32 ton/km 2 /yr of YS. Good correlations were observed between terrestrial n-alkanes and TOC in the sediments of SBS and northern YS, but they were poor for southern YS, meanwhile higher ratios of nC27 + nC29 + nC31/nC15 + nC17 + nC19 (12 ± 6) were observed in SBS, and lower in YS (2.2 ± 1.0), suggesting the Yellow River discharge was an important source of terrestrial organic matter to the shelf.

Reactive Iron and Iron‐Bound Organic Carbon in Surface Sediments of the River‐Dominated Bohai Sea (China) Versus the Southern Yellow Sea

“…TOC contents in the BHS sediments (0.20–1.04%) are within the ranges previously reported for the sea (Gao et al, ; Li et al, ; Sun et al, ), while TOC mean (0.62 ± 0.20%) in this study is markedly higher than that (0.25–0.45%) reported by previous authors (Hu et al, ; Lin et al, ; D. Liu et al, ; Qin et al, ). This is probably due to the fact that more samples in this study were from areas with higher clay fractions delineated by Hu et al () because OC is usually enriched in fine‐grained fractions as demonstrated by a good positive correlation ( R 2 = 0.48, p < 0.01) between the percentages of clay fraction and TOC contents in this study (Figure a) and also in many other studies (Poulton & Raiswell, ; Roy et al, ; Zhu et al, ).…”

“…TOC contents in the BHS sediments (0.20-1.04%) are within the ranges previously reported for the sea (Gao et al, 2013;Sun et al, 2018), while TOC mean (0.62 ± 0.20%) in this study is markedly higher than that (0.25-0.45%) reported by previous authors (Hu et al, 2009;Lin et al, 2014;D. Liu et al, 2015;Qin et al, 2011).…”

Macroscale distribution of virioplankton and heterotrophic bacteria in the Bohai Sea

“…This result is unique compared with previous findings in other ocean areas [Riegman et al, 2003;Wang et al, 2010]. According to the current analysis, this may be related to the large accumulation of organic matter [Lin et al, 2014] in the bottom waters during winter, which support the growth of abundant heterotrophic bacteria and virioplankton. Additionally, owing to the influence of the Yellow Sea Warm Current in winter, there is significant water exchange in this area, which greatly changes the ecological environment and brings warm and saline water towards Bohai Sea [Xu et al, 2009]; thus, the abundances of heterotrophic bacteria and virioplankton are greatly changed.…”

Distribution and sources of organic matter in surface sediments of Bohai Sea near the Yellow River Estuary, China

“…This eutrophication has resulted in frequent harmful algal blooms and the development of low oxygen environments near the sea floor (Shan et al, 2013). The YR is a massive source of terrestrial organic carbon, but there are only limited data on organic matter distribution and origin in sediments near the YR mouth and in the adjacent shallow Bohai and Yellow Seas, although they constitute a major carbon sink of global significance (Hu et al, 2009;Lin et al, 2014). Whereas Hu et al (2009) studied the OM distribution in the BS and noted that the YR delta and fore-delta are the main carbon sinks, there is yet no relative estimate of the proportions of allochthonous (terrigenous) and autochthonous (marine phytoplankton) material in the sediments, and little information is available on the isotopic composition of sedimentary nitrogen that would shed light on dominant nitrogen sources.…”