A variety of chemical compounds that persist in the environment can be used as tracers of a variety of processes in ocean systems, both those occurring in the recent past, as well as being used to trace changes over paleo timescales. There has been recent interest in using archaeal and bacterial glycerol-dialkyl-glycerol tetraether (GDGT) lipids as proxies in paleoceanography and biogeochemistry, and such studies have been an area of recent research. However, there is a need to constrain and ground-truth the measurements in order to validate the biogeochemical interpretations being made by the various research groups. Accurate pure chemical standards are critical for such validation. Current methods involve calibrating a synthetic standard regularly against a known quantity of a pure, authentic GDGT. However, as very few labs have access to the authentic GDGT's, there is a lack of strict calibration in paleoproxy studies. Therefore, researchers from Harvard University have proposed to generate pure GDGT's to meet this need. The goal of this research is to extract these lipids from sediments, purify the individual compounds, and create reference standards that can be used in quantitative and radiocarbon work. Due to the scientific popularity of GDGT's as tracers, it is the researchers' goal to make the entire project "open access" to the community. When generated, laboratories can potentially use these standards to check their preparation methods and/or analytical methods through instrument calibration. Additionally, these materials can serve as isotope reference materials, similar to those available from other institutions. The broader impacts of this research relate to the service that the proposed standards will provide to the research community. In addition, undergraduate, graduate, and high school students will benefit from training opportunities during the project.

Project Report

The paleo-proxy applications (TEX86 and MBT/CBT) are used to reconstruct records of sea surface temperature (SST) and mean annual air temperature (MAAT), respectively. Both of these proxies rely on accurate measurements of lipids known as glycerol-dialkyl-glycerol tetraether lipids (GDGTs). In many episodes of geologic history, these organic paleoproxy records are the only means available to attempt to understand past temperatures. It is therefore important that there be an accurate method for both absolute and relative quantification of these lipids, but to date it has been challenging to achieve this goal, due to a lack of good reference materials. With the support of the US National Science Foundation (NSF), our lab has prepared large quantities of two purified and quantified GDGT lipids. We are now distributing them to the international scientific community. Our goal is to assist the biogeochemical and paleoceanography communities through improved assessments of GDGT distributions and their isotopic compositions. Specifically we hope to enable standardization of the methods for quantification of GDGTs. We have offered these reference materials for free to our international and national colleagues, and to date have sent them to the USA, China, the Netherlands, several labs in Germany, and to Sweden, with likely many more countries to follow.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Donald L. Rice
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Harvard University
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