Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration
Naafs, BDA; Gallego-Sala, AV; Inglis, GN; et al.Pancost, RD
Date: 10 February 2017
Journal
Organic Geochemistry
Publisher
Elsevier
Publisher DOI
Abstract
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to
reconstruct past terrestrial temperature and soil pH. Here we compare all available
modern soil brGDGT data (n=350) to a wide range of environmental parameters to
obtain new global temperature calibrations.
We show that soil moisture index (MI), a ...
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to
reconstruct past terrestrial temperature and soil pH. Here we compare all available
modern soil brGDGT data (n=350) to a wide range of environmental parameters to
obtain new global temperature calibrations.
We show that soil moisture index (MI), a modeled parameter that also takes
potential evapotranspiration into account, is correlated to the 6-methyl brGDGT
distribution but does not significantly control the distribution of 5-methyl brGDGTs.
Instead, temperature remains the primary control on 5-methyl brGDGTs. We propose the following global calibrations: MAAT soil = 40.01 x MBT’5me − 15.25 (n=350, R2 22 = 23 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 x MBT’5me - 4997.5 (n=350, R2 24 = 0.63, RMSE = 1779 °C).
Recent studies have suggested that factors other than temperature can impact
arid and/or alkaline soils dominated by 6-methyl brGDGTs. As such, we develop new
global temperature calibrations using samples dominated by 5-methyl brGDGTs only
(IR6me<0.5). These new calibrations have significantly improved correlation
coefficients and lower root mean square errors (RMSE) compared to the global
calibrations: MAATsoil’ = 39.09 x !"#!!"
! − 14.50 (n=177, R2 30 = 0.76, RMSE =
4.1 °C) and GDD0 soil’ = 13498.8 x !"#!!"
! − 4444.5 (n=177, R2 31 = 0.78, RMSE =
1326). We suggest that these new calibrations should be used to reconstruct terrestrial
climate in the geological past; however, care should be taken when employing these
calibrations outside the modern calibration rang
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