Flooding sedimentation at the Yellow River mouth, China

<p>Chinese Huanghe (Yellow River) provides an extreme case of human controlled large river system. Since 2002, a unique Water-Sediment Regulation （WSR） regime was implemented annually through Xiaolangdi Dam to buffer pool infilling and scour the hanging riverbed. This involves transfers of large-volume of water and sediment between reservoirs, becoming a human-made flooding event. 37 surface sediments 8 box cores sampled during the 2018 WSR were analyzed for grain-size, C/N, <sup>13</sup>C, radionuclides, etc. Satellite images together with high-resolution bathymetric data were incorporated to depict the flooding sedimentation at the river mouth. The results show that <sup>7</sup>Be and <sup>210</sup>Pb activity is pretty low, implying its incapability of tracing flood sediments at the Huanghe River mouth. The results also uncover that a majority of the sediment was deposited in the vicinity of the river mouth where the water depth is less than 15 m. Two depocenters with a maximum thickness of 9 m were formed expanding within a very restricted area, which was largely controlled by tidal currents.</p>

Ubiquitous production of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in global marine environments: a new source indicator for brGDGTs

Presumed source specificity of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from bacteria thriving in soil/peat and isoprenoid GDGTs (iGDGTs) from aquatic organisms led to the development of several biomarker proxies for biogeochemical cycle and paleoenvironmental reconstructions. However, recent studies reveal that brGDGTs are also produced in aquatic environments besides soils and peat. Here we examined three cores from the Bohai Sea, and found distinct difference in brGDGT compositions varying with the distance from the Yellow River mouth. We thus propose an abundance ratio of hexamethylated to pentamethylated brGDGT (IIIa ∕ IIa) to evaluate brGDGT sources. The compilation of globally distributed 1354 marine sediments and 589 soils shows that the IIIa ∕ IIa ratio is generally < 0.59 in soils and 0.59–0.92 and > 0.92 in marine sediments with and without significant terrestrial inputs, respectively. Such disparity confirms the existence of two sources for brGDGTs, a terrestrial origin with lower IIIa ∕ IIa and a marine origin with higher IIIa ∕ IIa, which is likely attributed to a generally higher pH and the production of brGDGTs in cold deep water in marine waters. The application of the IIIa ∕ IIa ratio to the East Siberian Arctic Shelf proves it to be a sensitive source indicator for brGDGTs, which is helpful for accurate estimation of organic carbon source and paleoclimates in marine settings.

Ubiquitous production of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in global marine environments: a new source indicator for brGDGTs

Presumed source specificity of branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) led to the development of several biomarker proxies for biogeochemical cycle and paleoenvironment. However, recent studies reveal that brGDGTs are also produced in aquatic environments besides soils and peat. Here we examined three cores from the Bohai Sea and found distinct difference in brGDGT compositions varying with the distance from the Yellow River mouth. We thus proposed an abundance ratio of hexamethylated to pentamethylated brGDGT (IIIa / IIa) to evaluate brGDGT sources. The compiling of globally distributed 1354 marine sediments and 589 soils shows that the IIIa / IIa ratio is generally < 0.59 for soils, 0.59–0.92 and > 0.92 for marine sediments with and without significant terrestrial inputs, respectively. Such disparity confirms the existence of two sources of brGDGTs, a terrestrial origin with lower IIIa / IIa and a marine origin with higher IIIa / IIa, likely due to different pH influence. The application of the IIIa / IIa ratio to the East Siberian Arctic Shelf proves it a sensitive source indicator for brGDGTs, which is helpful for accurate estimation of organic carbon source and paleoclimates in marine settings.