Introducing global peat-specific temperature and pH calibrations based on brGDGT bacterial lipids
Naafs, BDA; Inglis, GN; Zheng, Y; et al.Amesbury, MJ; Biester, H; Bindler, R; Blewett, J; Burrows, MA; del Castillo Torres, D; Chambers, FM; Cohen, AD; Evershed, RP; Feakins, SJ; Gallego-Sala, AV; Gandois, L; Gray, DM; Hatcher, PG; Honorio Coronado, EN; Hughes, PDM; Huguet, A; Kononen, M; Laggoun-Defarge, F; Lahteenoja, O; Marchant, R; McClymont, E; Pontevedra-Ponbal, X; Ponton, C; Pourmand, A; Rizzuti, AM; Rochefort, L; Schellekens, J; De Vleeschouwer, F; Pancost, RD
Date: 31 January 2017
Journal
Geochimica et Cosmochimica Acta
Publisher
Elsevier
Publisher DOI
Abstract
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 ...
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 °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, R2 65 = 0.58, RMSE = 0.8) and
the degree of methylation of brGDGTs is positively correlated with MAAT,
MAATpeat (°C) = 52.18 x MBT5me’ – 23.05 (n = 96, R2 67 = 0.76, RMSE = 4.7 °C).
3
These peat-specific calibrations are distinct from the available mineral soil
calibrations. In light of the error in the temperature calibration (~ 4.7 °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 (~15.2 kyr), we demonstrate that MAATpeat yields
absolute temperatures and relative temperature changes that are consistent with those
from other proxies. In addition, the application of MAATpeat 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
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