Occurrence and distribution of tetraether membrane lipids in soils: Implications for the use of the TEX86 proxy and the BIT index

Abstract

A diverse collection of globally distributed soil samples was analyzed for its glycerol dialkyl glycerol tetraether (GDGT) membrane lipid content. Branched GDGTs, derived from anaerobic soil bacteria, were the most dominant and were found in all soils. Isoprenoid GDGTs, membrane lipids of Archaea, were also present, although in considerably lower concentration. Crenarchaeol, a specific isoprenoid membrane lipid of the non-thermophilic Crenarchaeota, was also regularly detected and its abundance might be related to soil pH. The detection of crenarchaeol in nearly all of the samples is the first report of this type of GDGT membrane lipid in soils and is in agreement with molecular ecological studies, confirming the widespread occurrence of non-thermophilic Crenarchaeota in the terrestrial realm. The fluvial transport of crenarchaeol and other isoprenoid GDGTs to marine and lacustrine environments could possibly bias the BIT index, a ratio between branched GDGTs and crenarchaeol used to determine relative terrestrial organic matter (TOM) input. However, as crenarchaeol in soils is only present in low concentration compared to branched GDGTs, no large effect is expected for the BIT index. The fluvial input of terrestrially derived isoprenoid GDGTs could also bias the TEX 86 , a proxy used to determine palaeo surface temperatures in marine and lacustrine settings and based on the ratio of cyclopentane-containing isoprenoid GDGTs in marine and lacustrine Crenarchaeota. Indeed, it is shown that a substantial bias in TEX 86 -reconstructed sea and lake surface temperatures can occur if TOM input is high, e.g. near large river outflows.

Crenarchaeol dominates the membrane lipids of Candidatus Nitrososphaera gargensis, a thermophilic Group I.1b Archaeon

“…Figure 5). In addition, our findings confirm previous circumstantial evidence for crenarchaeol synthesis by Group I.1b Crenarchaeota based on the ubiquitous presence of crenarchaeol in soils (Weijers et al, 2006), and the significant correlation linking ammonia-oxidizing soil Archaea to crenarchaeol synthesis (Leininger et al, 2006). Our results signify that all cultivated representatives of Group I Crenarchaeota to date synthesize crenarchaeol, thus providing support for the suggested specificity of crenarchaeol to Archaea involved in ammonia oxidation (de la Torre et al, 2008).…”

“…In some tropical soils, however, the relative abundance of the crenarchaeol isomer is much higher and approaches ca. 40% of the local crenarchaeol concentration (Weijers et al, 2006). Members of the soil Group I.1b crenarchaeota with a GDGT composition similar to that of 'Ca.…”

Warming and environmental changes in the eastern North Sea Basin during the Palaeocene–Eocene Thermal Maximum as revealed by biomarker lipids

“…It is possible that the TEX86 records at our sites are biased for this time-interval. For instance, the TEX86 values can be affected by the input of soil-derived isoprenoid GDGTs which can be assessed by the BIT index (Weijers et al, 2006). including GDGTs, were substantially exposed to oxygen.…”

Application of the TEX86 temperature proxy to the southern North Sea

“…The GDGTs used for calculating the TEX 86 have also been detected in peat bogs and soils, albeit in relatively low concentrations Weijers et al, 2006a) and, when transported to the marine environment, may alter the TEX 86 signal. The GDGT composition of soils is, however, dominated by another type of GDGT (i.e., branched GDGTs) produced by anaerobic bacteria (Weijers et al, 2006b).…”

“…1), the isoprenoidal GDGT considered as a specific biomarker for the marine Crenarchaeota group I and the three main branched GDGTs produced by anaerobic soil bacteria . According to Weijers et al (2006a), the BIT index should be determined before carrying out any TEX 86 analyses in marine settings to make sure that TEX 86 -derived temperatures are not biased as a result of a large terrestrial input. In fact, the concentrations of the GDGT used for calculating the TEX 86 were on average 20-40 times greater in the water of the river Rhine than in the seawater of the southern North Sea (Tables 1 and 3).…”