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Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration

Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration
Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration
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: MAATsoil = 40.01 × − 15.25 (n = 350, R2 = 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 × − 4997.5 (n = 350, R2 = 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 × − 14.50 (n = 177, R2 = 0.76, RMSE = 4.1 °C) and GDD0 soil′ = 13498.8 × − 4444.5 (n = 177, R2 = 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 range.
0146-6380
48-56
Naafs, B.D.A.
b4e4a3c0-ef86-476f-a439-3ce7e192337a
Gallego-Sala, A.V.
9af1ab7d-cbf2-4db6-a1c1-0413499ac1b6
Inglis, G.N.
1651196d-916c-43cb-b5a0-9b3ecaf5d664
Pancost, R.D.
893ebd86-164b-437e-8d26-cfe0d5ed6b14
Naafs, B.D.A.
b4e4a3c0-ef86-476f-a439-3ce7e192337a
Gallego-Sala, A.V.
9af1ab7d-cbf2-4db6-a1c1-0413499ac1b6
Inglis, G.N.
1651196d-916c-43cb-b5a0-9b3ecaf5d664
Pancost, R.D.
893ebd86-164b-437e-8d26-cfe0d5ed6b14

Naafs, B.D.A., Gallego-Sala, A.V., Inglis, G.N. and Pancost, R.D. (2017) Refining the global branched glycerol dialkyl glycerol tetraether (brGDGT) soil temperature calibration. Organic Geochemistry, 106, 48-56. (doi:10.1016/j.orggeochem.2017.01.009).

Record type: Article

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 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: MAATsoil = 40.01 × − 15.25 (n = 350, R2 = 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 × − 4997.5 (n = 350, R2 = 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 × − 14.50 (n = 177, R2 = 0.76, RMSE = 4.1 °C) and GDD0 soil′ = 13498.8 × − 4444.5 (n = 177, R2 = 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 range.

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More information

Accepted/In Press date: 17 January 2017
e-pub ahead of print date: 10 February 2017
Published date: April 2017

Identifiers

Local EPrints ID: 437531
URI: http://eprints.soton.ac.uk/id/eprint/437531
ISSN: 0146-6380
PURE UUID: b9fd87b1-5168-4708-b23e-33cee49cbbf6
ORCID for G.N. Inglis: ORCID iD orcid.org/0000-0002-0032-4668

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Date deposited: 04 Feb 2020 17:30
Last modified: 17 Mar 2024 04:00

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Contributors

Author: B.D.A. Naafs
Author: A.V. Gallego-Sala
Author: G.N. Inglis ORCID iD
Author: R.D. Pancost

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