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Compound-Specific Radiocarbon Analysis of Lake Sediments: A New Tool for Dating and Reconstruction of Carbon Dynamics of Soils Through the Holocene

Applicant Bernasconi Stefano
Number 119950
Funding scheme Project funding
Research institution Geologisches Institut ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.06.2008 - 31.05.2011
Approved amount 340'556.00
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All Disciplines (3)

Discipline
Geochemistry
Pedology
Hydrology, Limnology, Glaciology

Keywords (10)

compound-specific 14C; Organic geochemistry; Soil carbon; Holocene; radiocarbon; Paleolimnology; Carbon cycle; lipid biomarkers; lake sediment; soils

Lay Summary (English)

Lead
Lay summary
Over the past decades, much progress has been made in the understanding of past climate and environments, and much of this information has come from the bottom of lakes and oceans, where plants, algae and eroded soil accumulate over time (this accumulated material is called sediment). However, there are also still many things unknown about how the global climate has changed through time - important information if we want to predict future. There are practical issues that make research in this direction difficult. In this project, we try to solve two of these issues, using the relatively new technique of compound-specific radiocarbon analysis. That is, determining the age of molecules that derive from living organisms, for instance plant or algal remains, with radiocarbon dating (a technique also commonly used to determine how old archeological sites are). In the Climate Geology group at the ETH we are able to do such molecular-scale separations, and since last year, small-scale radiocarbon measurements can be performed at the Paul Scherrer Institute.
The first goal of the project is to improve understanding of soil organic carbon (SOC) and how it has changed over the course of centuries and millenia. Such knowledge is important for predictions about the carbon dioxide (CO2) content in the atmosphere, because SOC is an important part of the global carbon cycle. SOC consists mainly of dead plant material that has been sitting in the soil for a certain amount of time. This carbon has thereby 'escaped' from the atmosphere when it was used by the plants to grow. However, soil bacteria also slowly eat some of the SOC and breathe it out again as CO2, and the total amount of SOC is thus result of the balance between input of plant material and output by bacteria. By looking at the age of soil-derived components that have accumulated in lake sediments (e.g. 3500 yr at 1m depth, and 4000 yr at 2m depth), and comparing that of the age of the lake sediments itself (e.g. 1000 yr at 1m and 2000 yr at 2m), we gain insight in how the soil carbon pool has behaved through time (in this example, 2000yr ago soil carbon that eroded into the lake was on average 2000yr old, and 1000yr ago the soil carbon was 2500yr old).
Second, we can use molecular-scale radiocarbon analysis for dating. Often, the age of layer in a lake or ocean sediment can be determined on blown in material like leaves that were produced the same year. Their radiocarbon age is then representative for the time of deposition of that layer. However, sometimes there are no recognizable leaf remains and dating of the sediments is not possible, while such a sediment contains much information about the past. In this project we develop further the technique of radiocarbon dating on a molecular scale. The origin of molecules (for instance algae that grow in the lake, die the same year, and end up in the sediment) can be determined using chemical analysis. In this way, dating may be possible on sediments while it is not possible by traditional methods.
PhD student: Axel Birkholz. Primary Advisor: Dr. Rienk Smittenberg. Radiocarbon specialist: Dr. Irka Hajdas. Supervisor: Dr. Stefano Bernasconi http://www.climategeology.ethz.ch
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
134847 Compound-Specific Radiocarbon Analysis of Lake Sediments: A New Tool for Dating and Reconstruction of Carbon Dynamics of Soils Through the Holocene: part II 01.06.2011 Project funding
135908 Pushing the size limits of radiocarbon analysis 01.09.2011 International Exploratory Workshops

Abstract

Over the past decades, much progress has been made in the understanding of past climate and environments, and much of this information has been derived from lake and ocean sedimentary records. However, there are also still many gaps in the knowledge of the global climate change, and there are practical issues that hamper research in this direction. We propose to tackle two of these issues using the relatively new technique of compound-specific radiocarbon analysis. First, we aim at improving our understanding of the build-up and dynamics of the terrestrial soil organic carbon (SOC) pool. SOC constitutes an important reservoir in the global carbon cycle and, therefore, a better knowledge of its dynamics is of paramount importance for the prediction of its behavior as a source or sink under increasing atmospheric CO2 contents. This will be done by building on the successful approach of Smittenberg et al. (2006) using the radiocarbon ages of soil-derived molecular compounds and organic matter fractions, as preserved in well-dated and well-constrained sedimentary records, and comparing those with the actual age of deposition of the sediment. Our second aim is to further develop the technique of compound-specific radiocarbon dating. Chronologies of natural archives like lake sediments are typically based on radiocarbon dating of organic material that has been deposited soon after its biosynthesis. However, only a small fraction of studied lakes contains recognizable terrestrial macrofossils that can be used for radiocarbon dating, more often sediments are barren of terrigenous macrofossils, making radiocarbon dating a challenge or even impossible. Some lakes also suffer from a 'hard water effect" caused by weathering of radiocarbon-free carbonate rocks, affecting the age of aquatic-derived organic matter. We thus propose to develop compound-specific radiocarbon dating of organic compounds derived from either terrestrial material that has not been pre-aged in the soils in the catchments or from an aquatic source if no hard water effect is present, as a tool to bypass the chronological problems that plague many important records of climate change.The proposed research will focus on the practical aspects of purification of individual compounds from the complex mixture of sedimentary organic matter, as well as on that of radiocarbon dating of small samples. For this, the modern techniques of high-performance liquid chromatography - mass spectrometry will be used, as well as the newly developed gas-source for sample introduction into an accelerator mass spectrometer (AMS), allowing radiocarbon analysis of very small samples.The proposed research has the potential to provide many new insights and to produce results with a wide applicability. One outcome will be a thorough and rigorous test of the potential of compound-specific radiocarbon dating for lacustrine sediments, which could be of great importance to the large and very active scientific community studying climate change of the last 40,000 years. Secondly, valuable knowledge will be gained about the development and evolution of refractory soil organic carbon over time, bearing directly on outstanding questions about carbon cycling and fluxes.Finally, through these studies we expect to further develop analytical methods for the determination of radiocarbon in organic compounds. These methods have applications not only in earth science but also in the detection of the origin and transformation of pollutants in the environment, and might also be useful as a non-invasive method for the determination of metabolic pathways and carbon cycling in complex natural microbial systems.
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