Origin of hydroxyl GDGTs and regular isoprenoid GDGTs in suspended particulate matter of Yangtze River Estuary

The Novel Hydroxylated Tetraether Index RI‐OH′ as a Sea Surface Temperature Proxy for the 160‐45 ka BP Period Off the Iberian Margin

“…One potential mechanism related to the enhanced summer upwelling is a bias toward the warm season for U K ′ 37 , though the increase in C 37 alkenone concentrations is relatively modest (Figures 3c, 3f, and 3i), whereas archeal producers may be more competitive for nutrients at the end of the upwelling, which may bias GDGT‐based proxies toward the cold season or larger export depths (Darfeuil et al., 2016). Alternatively, increased ammonia oxidation rates related to stronger upwelling could generate cold biases for at least TEX 86 and TEX 86 H (Hurley et al., 2016; Lawrence et al., 2020; Lü et al., 2019). A third possibility is that the particularly pronounced OH‐GDGT‐0 concentration peak compared to other archeal GDGTs (Figures 3 and ) is partly due to archaea other than Thaumarchaeota (Liu et al., 2012; Ma et al., 2020; Yang et al., 2019).…”

“…Alternatively, shifts in Thaumarchaeota communities (Polik et al, 2018) may have biased RI-OH′ and RI-OH values. However, most studies suggesting ecological effects and other nonthermal effects on archeal GDGT distributions are restricted to iGDGTs and their derived TEX 86 paleothermometer (e.g., Elling et al, 2014Elling et al, , 2015Evans et al, 2018;Hurley et al, 2016Hurley et al, , 2018Junium et al, 2018;Lawrence et al, 2020;Lü et al, 2019;Ma et al, 2020;Park et al, 2018;Polik et al, 2018;Qin et al, 2015;Wei et al, 2020;Xie et al, 2014). In principle, bioturbation could also be invoked to explain the contrasts between RI-OH′ and U K ′ 37 , notably during the Heinrich-like event GS22 which has particularly contrasting relative decreases in OH-GDGT and C 37 alkenone concentrations ( Figure S13).…”

Comparison of the U<sub>37</sub><sup>K<sup>′</sup></sup>, LDI, TEX<sub>86</sub><sup>H</sup>, and RI-OH temperature proxies in sediments from the northern shelf of the South China Sea

“…3d). In addition, the nutrient distribution in the river is characterized by high N : P ratios of up to ∼ 100 : 1 (Dai et al, 2008;Lu and Gan, 2015;Xu et al, 2008;Zhang et al, 2013). We surmise that such an input of an unbalanced nutrient ratio could stimulate the growth, though not prominent blooms, of alkenone-producing haptophytes, e.g., E. huxleyi, in the oligotrophic shelf waters during the EASM period, since both in situ investigations and experiments have reported that E. huxleyi have a competitive advantage over other phytoplankton at high N : P ratios (Riegman et al, 1992;Tyrrell and Taylor, 1996).…”

Western Mediterranean Sea Paleothermometry Over the Last Glacial Cycle Based on the Novel RI‐OH Index

“…To date, de Bar et al (2019) and Kremer et al (2018) alone have used RI-OH and RI-OH′, respectively. In addition, only a few studies have assessed potential biases for RI-OH and RI-OH′, such as inputs of terrestrial OH-GDGTs, seasonal biases, and OH-GDGT production in subsurface waters (Kang et al, 2017;Lü et al, 2015Lü et al, , 2019Yang et al, 2019;Zhu et al, 2016). 20-cm-thick sandy layer at the top.…”