Production of Branched Tetraether Lipids in the Lower Pearl River and Estuary: Effects of Extraction Methods and Impact on bGDGT Proxies

Abstract

Branched glycerol dibiphytanyl glycerol tetraethers (bGDGTs) are known as bacterial lipids that occur widely in terrestrial environments, particularly in anaerobic peat bogs and soil. We examined the abundance and distribution of bGDGTs in both core (C) and polar (P) lipid fractions from the water column and surface sediments in the lower Pearl River (PR) and its estuary using two extraction methods (sonication vs. Bligh and Dyer). A number of soil samples in the lower PR drainage basin were also collected and extracted for bGDGTs using the sonication method. The results showed aquatic production of bGDGTs as supported by substantial abundances of P-bGDGTs in the water column and sediment samples. The bGDGT-based proxies (BIT, CBT, and MBT) were not affected by the method of extraction when C-bGDGTs were analyzed; in such case, the pHCBT of the sediments reflected the soil pH of the lower PR drainage basin, and the temperature close to the annual mean air temperature (MAT) in the lower PR basin. On the other hand, the P-bGDGT-derived proxies were inconsistent between the two methods. The P-bGDGTs (particularly those extracted using the sonication method) may not be reliable indicators of annual MATs.

Alkenone and tetraether lipids reflect different seasonal seawater temperatures in the coastal northern South China Sea

“…The BIT index, a proxy based on the relative abundance of soil derived branched tetraethe r lipids vs. crenarchaeo l for estimating the relative contribution of soil organic matter (OM) to marine sediments (Hopmans et al, 2004;Weijers et al, 2006 ), exhibits values between 0.90 and 0.99 in our soil and river samples upstream of the PRE. In the PRE, BIT decreases from >0.9 in the sediments at the freshwater entrance to <0.4 at the PRE mouth (Strong et al, 2012;Zhang et al, 2012 ), suggestive of a reducing soil OM contribution along the flow path from terrestrial to marine environments. For our cores, BIT values are 0.20 ± 0.03, 0.22 ± 0.03, 0.17 ± 0.02, 0.13 ± 0.02 and 0.12 ± 0.01 in cores A9, A8, A7, A6 and A5, respectivel y, exhibiting a slightly shoreward increasing trend.…”

Sources, distributions, and early diagenesis of sedimentary organic matter in the Pearl River region of the South China Sea

“…The C3 plant end-member value for δ 13 C was −29.0‰ (Yu et al, 2010) and was 7.00 mg/100 mg OC for Λ 8 (Tesi et al, 2007). The soil end-member value was − 24.1‰ for δ 13 C, which represents an average δ 13 C value of soils in the Pearl River (Yu et al, 2010;Zhang et al, 2012). The marine endmember values for δ 13 C and Λ 8 were −20.0‰ and 0 mg/100 mg OC, respectively ( Fig.…”

Branched tetraether lipids in Chinese soils: Evaluating the fidelity of MBT/CBT proxies as paleoenvironmental proxies

“…The analytical procedure followed Schouten et al (2007) that was modified by Zhang et al (2012). Briefly, 10-µL polar fractions were injected and peak separation was accomplished by using an Alltech Prevail Cyano column (150 mm×2.1 mm, 3 µm).…”

“…Sci China Earth Sci, in revision determined following a modified procedure of Zhang et al (2012). Briefly, an aliquot of freeze-dried soil sample was treated with 10% HCl to remove bicarbonate.…”

“…The occurrence and distribution of brGDGTs in some of these environments have been reported by a rapid growing number of publications in recent years (e.g., Wang et al, 2012;Zhang et al, 2012;Liu et al, 2013;Yang et al, 2014;Ding et al, 2015). In particular, Yang et al (2014) proposed new calibration models for Chinese soils using over 100 samples collected from different climatic regions, particularly the semiarid and arid loess regions.…”