Browsing by Subject "DIALKYL GLYCEROL TETRAETHERS"
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(2017)Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids from Bacteria and Archaea that are ubiquitous in a range of natural archives and especially abundant in peat. Previous work demonstrated that the distribution of bacterial branched GDGTs (brGDGTs) in mineral soils is correlated to environmental factors such as mean annual air temperature (MAAT) and soil pH. However, the influence of these parameters on brGDGT distributions in peat is largely unknown. Here we investigate the distribution of brGDGTs in 470 samples from 96 peatlands around the world with a broad mean annual air temperature (-8 to 27 degrees C) and pH (3-8) range and present the first peat-specific brGDGT-based temperature and pH calibrations. Our results demonstrate that the degree of cyclisation of brGDGTs in peat is positively correlated with pH, pH = 2.49 x CBTpeat + 8.07 (n = 51, R-2 = 0.58, RMSE = 0.8) and the degree of methylation of brGDGTs is positively correlated with MAAT, MAAT(peat) (degrees C) = 52.18 x MBT'(5me) - 23.05 (n = 96, R-2 = 0.76, RMSE = 4.7 degrees C). These peat-specific calibrations are distinct from the available mineral soil calibrations. In light of the error in the temperature calibration (similar to 4.7 degrees C), we urge caution in any application to reconstruct late Holocene climate variability, where the climatic signals are relatively small, and the duration of excursions could be brief. Instead, these proxies are well-suited to reconstruct large amplitude, longer-term shifts in climate such as deglacial transitions. Indeed, when applied to a peat deposit spanning the late glacial period (similar to 15.2 kyr), we demonstrate that MAAT(peat) yields absolute temperatures and relative temperature changes that are consistent with those from other proxies. In addition, the application of MAAT(peat) to fossil peat (i.e. lignites) has the potential to reconstruct terrestrial climate during the Cenozoic. We conclude that there is clear potential to use brGDGTs in peats and lignites to reconstruct past terrestrial climate. (C) 2017 The Authors. Published by Elsevier Ltd.
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(2022)To reconstruct changes in vegetation, temperature, and sediment geochemistry through the last 6.5 cal ka BP, in the Subcarpathian belt of the Eastern Carpathians (Romania), pollen, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and X-ray fluorescence analyses have been integrated. Pollen and brGDGTs (a bacterial lipid biomarker proxy) are used as paleothermometers for reconstructing the mean annual air temperature (MAAT) and mean temperature above freezing (MAF), respectively. Both proxies show roughly consistent records. The highest MAAT and MAF occurs during the oldest part of the record (from 6.5 to 4.2 cal ka BP), and the Middle to the Late Holocene shift is marked by a prominent decrease in temperature between 5.4 and 4.2 cal ka BP, coinciding with Bond event 4 and 3. This transition is coeval with a decrease in summer insolation, shift from consistent NAO-conditions to a predominance of NAO+ phase and coincides with the beginning of the Neoglacial cooling in northern latitudes. The warm bias in the MAF reconstruction during the Late Holocene is explained as a change in the lipid provenance or in the composition of the brGDGT producers after 4.2 cal ka BP.
