Evaluating global temperature calibrations for lacustrine branched GDGTs: Seasonal variability, paleoclimate implications, and future directions

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in lake sediments are increasingly used to investigate past terrestrial temperatures. brGDGTs are ubiquitous in sedimentary environments, well-preserved, and the number of methyl groups in different brGDGTs is generally controlled by temperature. Current brGDGT calibrations largely rely on empirical correlations between the relative abundances of different brGDGTs in surface sediments and either mean annual or warm season air temperatures. These approaches may introduce complications in global temperature calibrations due to differences in the seasonality of temperature and variations in brGDGT production with latitude that are difficult to constrain. Here, we report new brGDGTs data from lake surface sediments obtained throughout the tropics including South America (n 1/4 57), East Africa (n 1/4 21), and Southeast Asia (n 1/4 13), and revisit globally distributed brGDGT data. We find a uniform response of brGDGTs to mean annual air temperature across the tropics despite differences in the environmental and geological conditions in different regions highlighting the dominant influence of temperature on brGDGT distributions. brGDGTs in mid- and high latitude sediment show a qualitatively similar but quantitatively different response to those in the tropics. We show that temperature seasonality can partially explain the latitudinal differences, implying the need for latitudinally-dependent brGDGT calibrations and/or improved observations and models to constrain seasonal effects on brGDGTs. Combining our new data with previously published brGDGT data, we develop and apply improved temperature calibrations.(c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) preserved in lake sediments are widely used to study past terrestrial temperatures. The distribution of brGDGTs is influenced by temperature, and current calibration methods rely on correlations with surface sediments. However, these methods may introduce complications in global temperature calibrations due to differences in temperature seasonality and brGDGT production with latitude. This study examines brGDGT data from tropical regions and finds a uniform response to mean annual air temperature, highlighting the dominant influence of temperature. Moreover, the study suggests the need for latitudinally-dependent calibrations or improved observations/models to account for seasonal effects on brGDGTs.