Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids found in soils and sediments and their relative abundance correlates with temperature and pH, enabling them to be used as proxies in reconstructing past climatic and environmental conditions. However, the potential for other environmental variables, such as nutrient concentration, to affect brGDGT distributions remains largely unexplored. We have examined the influence of a suite of environmental factors, including temperature, lake water and sediment chemistry, and lake morphometry on brGDGT concentration and distributions in the surface sediments of 111 lakes in East Africa. We found that temperature was the major control on the distributions, while the influence of pH was relatively minor. Water depth also had a minor but statistically significant influence, perhaps due to the relationship between lake depth and deep water anoxia. Water column nutrient concentration did not have a significant effect on the distributions or concentration. We further explored the potential for these variables to affect brGDGT temperature reconstruction by examining the correlation between them and the residuals of our brGDGT temperature calibration. We found that, while the distribution of some cyclized brGDGTs may be influenced by pH and other environmental variables, they are necessary in brGDGT calibration equations in order to accurately reconstruct temperature, likely due to covariation between temperature and other environmental variables. While surface water pH correlated with the relative abundance of certain brGDGTs, caution should be exhibited when using brGDGTs as a pH proxy because of systematic calibration errors.
Bibliographical noteFunding Information:
This work was conducted with funds from the American Chemical Society Petroleum Research Fund and the National Science Foundation awarded to J.M.R and also received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC Grant Agreement No. . Fieldwork was sponsored by US National Geographic Society Grants 7999-06 and 8938-11 , the Research Foundation of Flanders Grants G.0528.07N and G.0096.12N , and the Federal Science Policy of Belgium through project SD/BD/03 ‘CLANIMAE’ and an Action 1 grant to H.E.
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