Distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from China and Nepal

Abstract

[1] Glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in surface sediments from 24 lakes in China and Nepal were analyzed. The result shows that branched GDGT lipids occur widely in the studied lake sediments. The different distribution of branched GDGTs between the Chinese soils from Weijers et al. (2007b) and the Chinese lake sediments indicates that the branched GDGTs in the lacustrine sediment are the mixture of allochthonous and autochthonous branched GDGTs. Our result supports the suggestion that temperature is the principal factor affecting the distribution of GDGTs. Seasonality, sources, and precipitation increase the uncertainty of the correlation between the methylation index of branched tetraethers (MBT)/cyclization ratio of branched tetraethers (CBT) proxy and the temperature. The correlations of the MBT/CBT index with mean annual air temperature (T) for the global lakes are T = 6.803 − 7.062 × CBT + 37.090 × MBT (n = 139, p < 0.0001, R 2 = 0.62, and RMSE = 5.24°C); for the global lakes with pH < 8.5, T = 3.949 − 5.593 × CBT + 38.213 × MBT (n = 100, p < 0.0001, R 2 = 0.73, and RMSE = 4.27°C). The significant correlation suggests that the MBT/CBT proxy might be used as a potential paleotemperature proxy in the limnic environment. The MBT/CBT proxy provides an independent way to evaluate and verify the sensitivities of the different proxies for paleotemperature reconstruction from lacustrine sediments.

Transport of branched tetraether lipids from the Tagus River basin to the coastal ocean of the Portuguese margin: consequences for the interpretation of the MBT'/CBT paleothermometer

“…It is well known that brGDGT soil calibrations differ from those reported for aquatic environments (Tierney et al, 2010;Zink et al, 2010;Pearson et al, 2011;Sun et al, 2011;Loomis et al, 2012). However, calibrations for river water have not yet been reported.…”

“…10b), with the largest changes observed for the IPL-derived brGDGTs. MBT' (and MBT) are also related to temperature in aquatic systems (Tierney et al, 2010;Zink et al, 2010;Pearson et al, 2011;Sun et al, 2011). Hence, MBT' could be used as evidence for in situ production of brGDGTs in the river as MBT' would then follow the changes in temperature over the annual cycle, whereas in case of a dominant soil origin for the brGDGTs, this would not be expected because of their residence time in soils .…”

Calibrating the glycerol dialkyl glycerol tetraether temperature signal in speleothems

“…In the Weijers et al (2007a) the original soil calibration had an r 2 of 0.77 with a standard error of 5°C (Weijers et al, 2007b). In a global lakes calibration, Sun et al (2011) reported r 2 = 0.62, with a standard error of 5.2°C across the whole data set, and r 2 = 0.73 with an error of 4.3°C when highly alkaline lakes were excluded. A recent recalibration of the MBT/CBT for soils reported an r 2 of 0.59 with a standard error of 5°C (Peterse et al, 2012).…”

“…Fig. 9 shows plots of measured vs calculated MAT using our speleothem based calibration, with the relevant regression lines from the equations of Sun et al (2011) and Weijers et al (2007a). The speleothem correlations have a lower slope than either of the other calibra- tions, and produces intermediate calculated temperatures, which begin to converge with the lakes calibration in colder samples (<10°C) and the soils calibration in hotter climates (>20°C).…”

“…(8). Black dashed line shows the regression trend using the soils calibration of Weijers et al (2007a), grey dotted line shows the regression trend using the lakes calibration of Sun et al (2011). ple groups when our TEX 86 , and MBT/CBT equations (calibrated to surface MAT) are applied. It can be seen that there is variation in the precision of the two proxies, with TEX 86 showing a smaller standard deviation at Wellington Caves, while the MBT/CBT proxy has a lower standard deviation at Bats Ridge.…”