Linking Archaeal Membrane Lipids and Ecology in Great Lakes: Understanding the TEX86 Paleotemperature Proxy

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ABSTRACTOCE-0452927Paleotemperature is difficult to measure in great lakes systems. The recent establishment of the relationship between crenarchaeotal membrane lipids (GDGTs) and mean annual lake surface temperature provides a powerful and much needed lake temperature reconstruction tool. Unfortunately, very little is known about the ecology of the Crenarchaeota from which these GDGT compounds are derived. Many questions remain before we can understand why the membrane lipids derived from the Crenarchaeota seem to reflect sea or lake surface temperatures. Presently, the potential for the membrane lipids from these archaea to be used for paleotemperature reconstruction is based solely on core-top calibrations from a diverse suite of marine and large lake environments.In this project, researchers at the University of Minnesota at Duluth will attempt to link the production of GDGTs in the water column of Lake Superior with specific aspects of the ecology of the Crenarchaeota in order to improve our understanding of the Crenarchaeota themselves as well as to determine whether the GDGT distribution identified in sediments reflects lake surface temperature and whether other factors are influencing the apparent temperature signal preserved by these crenarchaeotal membrane lipids.The research team will study the GDGT membrane lipids and nucleic acids of Crenarchaeota in the water columns and sediments of Lake Superior (North America) and Lake Malawi (East Africa). In Lake Superior, they will identify the time of the year when these compounds are most abundance in settling particulate organic matter and their fluxes to the sediment using sediment traps. They will also intend to identify specific depths where these crenarchaeotal compounds are dominant by analyzing them in suspended particulate matter (SPM) at various depths in the water column. Finally, the diversity of GDGT membrane lipids will be compared with the diversity of archaeal communities in both SPM and sediments from Lakes Superior and Malawi to examine whether variations in archaeal diversity are reflected in GDGT distributions. The project outlined in this proposal is expected to lay the groundwork for understanding the mechanistic link between the TEX86 paleotemperature index and water temperature in great lakes. Ultimately, results from this study should lead to the confident application of the TEX86 index by other scientists to address continental paleoclimate questions in lake systems worldwide.Broader Impacts: The broader impacts of this project include training of graduate and undergraduate students, both in field methods as well as state-of-the-art analytical methods and enhancement of national and international scientific collaborations. This study will also greatly increase our understanding of the mechanistic links between the TEX86 paleotemperature proxy and archaeal communities in great lakes, giving us a useful tool to help understand past, present, and future global climate and environmental change.