Introducing global peat-specific temperature and pH calibrations based on brGDGT bacterial lipids

Abstract

International audienceGlycerol 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 = 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 = 0.76, RMSE = 4.7 °C). 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

Atmospheric connections with the North Atlantic enhanced the deglacial warming in northeast China

“…Based on the global peat calibration of Naafs et al (2017), Hani peat temperatures range from −5.5 to 12.5 °C, with a mean value of 7 °C. The instrumental MAAT over the past 60 yr ranges from 3.8 to 7.4 °C in the region (data from http://data.cma.cn/), in agreement with the MAAT peat reconstructions for 3 surface peats from the Hani peatland: 5.5 °C, 3.5 °C, and 3.7 °C.…”

“…Here we apply to the northeast China Hani peat sequence a recently developed peat-specific proxy for mean annual air temperature (MAAT peat ) (Naafs et al, 2017) based on the distribution of bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs) (Sinninghe Damsté et al, 2000). This provides an exceptional opportunity to develop new temperature records and test the aforementioned hypotheses.…”

The role of elevated atmospheric CO<sub>2</sub> and increased fire in Arctic amplification of temperature during the Early to mid-Pliocene

“…Previously, it has been established that the degree of methyl 5 branching (expressed in the methylation index of branched tetraethers; MBT) is correlated with mean annual air temperature (MAT), and the relative amount of cyclopentane moieties (cyclization index of branched tetraethers; CBT) has been shown to correlate with both soil pH and mean annual air temperature (Weijers et al, 2007b). Because of the relationship of the distribution of these fossilized membrane lipids with these environmental parameters, it has been used for paleoclimate applications in different environments including coastal marine sediments (Bendle et al, 2010;Weijers et al, 2007a), peats 10 (Ballantyne et al, 2010;Naafs et al, 2017), paleosoils (Peterse et al, 2011;Zech et al, 2012), and lacustrine sediments (Loomis et al, 2012;Niemann et al, 2012;Pearson et al, 2011;Zink et al, 2010).…”

“…This has led to the definition of new indices and improved MAT calibrations based on the global soil 15 (De Jonge et al, 2014), peat (Naafs et al, 2017), and African lake (Russell et al, 2018) datasets.…”

“…Since the discovery that sedimentary brGDGTs can have varying sources, different calibrations have been developed depending on the origin of the brGDGTs, i.e. soil calibration (De Jonge et al, 2014), peat calibration (Naafs et al, 2017) and aquatic calibrations (i.e. Foster et al, 2016;Pearson et al, 2011;Russell et al, 2018).…”