Empirical Calibration of a Lipid-Based Paleothermometer in the Eastern Cordillera of Colombia
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Empirical Calibration of a Lipid-Based
Paleothermometer in the Eastern Cordillera of
Colombia
Veronica Anderson
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GDGT-based paleothermometers
• GDGT’s (Glycerol Dialkyl Glycerol Tetraethers) are membrane lipids produced by soil bacteria
• 9 individual branched GDGT’s• Slight structural variations represent
adaptations to different temperature regimes• Strong correlation between relative
abundances of GDGT’s and mean annual temperature
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Measurement of GDGT’s
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Measuring Paleotemperatures With GDGT’s
• Collect soil samples across the globe
• Measure GDGT abundances• Compare to nearby climate
station data• Create a statistical
correlation between measured GDGT’s and mean annual temperature (MAT) 𝑀𝐵𝑇 ′=
(𝐼𝑎+𝐼𝑏+𝐼𝑐 )(𝐼𝑎+𝐼𝑏+𝐼𝑐+ 𝐼𝐼𝑎+𝐼𝐼𝑏+𝐼𝐼𝑐+𝐼𝐼𝐼𝑎 )
𝐶𝐵𝑇=− log ( 𝐼𝑏+𝐼𝐼𝑏𝐼𝑎+𝐼𝑎 )
Peterse et al, 2012
𝑴𝑨𝑻=𝟎 .𝟖𝟏−𝟓 .𝟔𝟕×𝑪𝑩𝑻 +𝟑𝟏 .𝟎∗𝑴𝑩𝑻 ′
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Problems with current calibration
• Soil temperature not necessarily the same as temperature at climate station– can differ by as much as 8 degrees in our study!
• How much scatter does this mismatch introduce into the regression?
• How does this affect reported errors?• Can interpolation solve some of these
problems with site data?
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• Installed temperature loggers across elevation transect
• Recorded temperature every 10 mins for a year
• Measured GDGT’s in soils from each location
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3 different interpolations
Kriging Linear Interpolation
12-pt Spline
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0 5 10 15 20 25 30 350
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Soil GDGT Temperature Calibration
In-Situ Temperatre Loggers (R2 = 0.81)
Nearest Climate Station (R2 = 0.58)
Linear Interpolation (R2 = 0.87)
Kriging (R2 = 0.90)
Spline (R2 = 0.72)
1:1 Line
Measured Temperature (°C)
Calcu
ated
Tem
pera
ture
(°C)
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Conclusions
• Simple linear interpolation actually does a pretty good job!
• Original authors happened to pick a good interpolation scheme.
• R2 still = 0.8, even with in-situ temperature loggers → suggests that 20% of the variation in GDGT compounds cannot be explained by temperature alone!
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Future Work
Soil sample locations used by Peterse et al, 2012
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Thanks for Listening!……Any Questions?