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

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)48-56
Number of pages9
JournalOrganic Geochemistry
Volume106
Early online date10 Feb 2017
DOIs
DateAccepted/In press - 17 Jan 2017
DateE-pub ahead of print - 10 Feb 2017
DatePublished (current) - 23 Apr 2017

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 × MBT5me  − 15.25 (n = 350, R2 = 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 × MBT5me  − 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 × MBT5me  − 14.50 (n = 177, R2 = 0.76, RMSE = 4.1 °C) and GDD0 soil′ = 13498.8 × MBT5me  − 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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    Rights statement: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Elsevier at https://doi.org/10.1016/j.orggeochem.2017.01.009 . Please refer to any applicable terms of use of the publisher.

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    Licence: CC BY-NC-ND

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