Variability of tetraether lipids in Yellow River-dominated continental margin during the past eight decades: Implications for organic matter sources and river channel shifts

• Published in: Organic geochemistry 2013-07, Vol.60, p.33-39
• Main Authors: Wu, Weichao, Zhao, Liang, Pei, Yandong, Ding, Weihua, Yang, Huan, Xu, Yunping
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Freshwater; Geochemistry; isoprenoids; lipids; Marine and continental quaternary; organic matter; rivers; sediments; soil; Soil and rock geochemistry; statistical models; Surficial geology
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2013.04.014

•High resolution record of tetraether lipids in Bohai Sea during past eight decades.•Sedimentary organic matter in Bohai Sea is dominated by soil organic matter.•The BIT index value is highly sensitive for the Yellow River channel shifts. Glycerol dialkyl glycerol tetraethers (GDGTs) and bulk organic geochemical parameters were examined for a short core from the Bohai Sea, a Yellow River-dominated continental margin. A three end member mixing model using branched/isoprenoid tetraethers (BIT) index, δ13C and C/N shows that the average fractions of soil, marine and plant organic matter (OM) during the period of 1933–2011 are 67.7% (38–92%), 26.1% (0–58%) and 6.2% (0–23%), respectively. Abrupt changes of sedimentary OM compositions around 1953, 1976 and 1996 are synchronous with the Yellow River mouth relocations. The BIT index values (0.33–0.80) present a stronger correlation with crenarchaeol abundance (R2=0.88) than branched GDGTs abundance (R2=0.27), suggesting that variations of marine Thaumarchaeota abundance rather than soil OM inputs is the first order factor controlling the BIT index values, although this proxy has been widely used for soil OM. The comparison between the BIT index, nutrient status and historical Yellow River sediment load indicates that the high sensitivity of the BIT index to the Yellow River channel shifts cannot be explained by a nutrient stimulation mechanism, but instead is likely caused by the restriction of Thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from Yellow River. Our study demonstrates that local conditions should be considered when applying the BIT index as an environmental proxy.