Abstract
The diversity and relative abundances of tetraether lipids produced by Thaumarchaeota in soils and sediments increasingly is used to assess environmental change. For instance, the TetraEther indeX of 86 carbon atoms (TEX86), based on archaeal isoprenoidal glycerol dialkyl glycerol tetraether (iGDGT) lipids, is frequently applied to reconstruct past sea-surface temperatures (SST). Yet, it is unknown how the ratio fully responds to environmental and or geochemical variations and if the produced signals are the adaptive response by Thaumarchaeota to climate driven temperature changes in the upper water column. We present the results of a four push-core transect study of surface sediments collected along an environmental gradient at the Cathedral Hill hydrothermal vent system in Guaymas Basin, Gulf of California. The transect crosses a region where advecting hydrothermal fluids reach 155 °C within the upper 21 cm below the seafloor (cmbsf) close to the vent center to near ambient conditions at the vent periphery. The recovered iGDGTs closest to the vent center experienced high rates of turnover with up to 94 % of lipid pool being lost within the upper 21 cmbsf. Here, we show that turnover is non-selective across TEX86 GDGT lipid classes and does not independently affect the ratio. However, as evident by TEX86 ratios being highly correlated to the Cathedral Hill vent sediment porewater temperatures (R2 = 0.84), the ratio can be strongly impacted by the combination of severe lipid loss when it is coupled to the addition of in situ iGDGT production from archaeal communities living in the vent sediments. The resulting signal overprint produces absolute temperature offsets of up to 4 °C based on the TEX86H-calibration relative to modern climate records of the region. The overprint is also striking given the flux of GDGTs from the upper water column that is estimated to represent ~93 % of the combined intact polar lipid (IPL) and core GDGT lipid pool initially deposited on the seafloor. A model to correct the overprint signal using IPLs is therefore presented that can similarly be applied to all near-surface marine sediment systems where calibration models or climate reconstructions are made based on the TEX86 measure.
Highlights
Archaeal and bacterial tetraether cellular membrane lipids mark common and structurally diverse compounds that are frequently used to track the presence of living and dead microorganisms in the geosphere (e.g. Schouten et al, 2002, 2004; Hopmans et al, 2004; Weijers et al, 2007; Lipp et al, 2008)
The utility of TetraEther indeX of 86 carbon atoms (TEX86) rests on the premise that isoprenoidal glycerol dialkyl glycerol tetraether (iGDGT) found in ocean bottom sediments are almost exclusively produced by marine planktonic Thaumarchaeota that inhabit the epipelagic zone (Wakeham et al, 2003; Tierney, 2014).TEX86-based lipids are required to be efficiently and continually transported from the upper water column to the underlying ocean floor sediments to produce a chemostratigraphic record of microbial response to changing SST conditions (Wuchter et al, 2005)
We demonstrate the commonly used TEX86 paleoclimate proxy can become heavily impacted by the ocean floor archaeal community
Summary
Archaeal and bacterial tetraether cellular membrane lipids mark common and structurally diverse compounds that are frequently used to track the presence of living and dead microorganisms in the geosphere (e.g. Schouten et al, 2002, 2004; Hopmans et al, 2004; Weijers et al, 2007; Lipp et al, 2008). TEX86 (TetraEther indeX with 86 carbon atoms (Schouten et al (2002) is the most widely used archaeal lipid-based paleotemperature proxy for marine environments (Table 1; Eq. 1). This proxy measures variations in the number of cyclopentyl rings within the hydrocarbon skeleton of a select range of archaeal core lipid (CL) classes The utility of TEX86 rests on the premise that iGDGTs found in ocean bottom sediments are almost exclusively produced by marine planktonic Thaumarchaeota that inhabit the epipelagic zone (Wakeham et al, 2003; Tierney, 2014).TEX86-based lipids are required to be efficiently and continually transported from the upper water column to the underlying ocean floor sediments to produce a chemostratigraphic record of microbial response to changing SST conditions (Wuchter et al, 2005)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call