Confocal Raman microscopy and its contribution to sclerochronology


Contact
Lars.Beierlein [ at ] awi.de

Abstract

Rising global temperatures, ocean acidification and rising sea levels: just three of many changes mankind will have to deal with in the future. A precise understanding of past warm phases is essential for successfully anticipating forthcoming change and mitigating its consequences. Understanding the connections of the complex global climate system during warm phases, when climate conditions were similar to what we can expect for the future, is a major task for palaeo-climate reconstructions. Since instrumental data are restricted to the last two centuries, past climates can only be revealed by proxy data. Fossil biogenic carbonates (e.g., molluscs, foraminifera) are key-sources of information for palaeo-climatic and palaeo-environmental reconstructions, as anatomical and/or geochemical properties of the carbonate can serve as proxies for certain environmental parameters. Confocal Raman microscopy (CRM) can play a central role in analysis and quality control of biogenic carbonate studies. CRM can identify mineral (and organic) phase(s) in marine biogenic carbonates at high spatial resolution (300 nm), i.e. it allows to identify taphonomic changes in the carbonate structure. Furthermore, this method is ideal to detect possible contaminations, e.g., resulting from shell preparation in the laboratory (e.g., by epoxy resin or super glue). CRM is also a valuable tool to identify and visualize growth increments within accretionally precipitated carbonate skeletons of marine organisms. Commonly used dyeing techniques (like e.g., Mutvei´s solution) are often inefficient when applied to fossil biogenic carbonates with low organic content. CRF can reveal shell formation processes at a very high spatial resolution, even in several million years old shell material Here, we demonstrate the potential of CRM supported analysis, using shells of the marine bivalve Arctica islandica. Its wide northern-boreal distribution, its relative abundance in the fossil record (present in the North Atlantic since at least 20 million years), its longevity (more than 400 years) and not least its high temporal resolution (seasonal and even daily information can be obtained) make it an exceptional bio-archive. Fossil shells, dated from Oligocene to Holocene, collected from the North Atlantic and the Mediterranean Sea, were analysed for their state of preservation by applying CRM. Since these shells are entirely built of aragonite (meta-stable polymorph of CaCO3) it makes them an ideal object for recrystallisation studies. In addition, CRM was used to visualize growth increments in the umbonal and the ventral shell portion at different spatial resolutions (μm to mm). Results were then compared to reflected light microscopy and staining methods in the same specimens.



Item Type
Conference (Talk)
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Not peer-reviewed
Publication Status
Published
Event Details
Jubiläumstagung der Paläontologischen Gesellschaft, 24 Sep 2012 - 29 Sep 2012, Berlin, Germany.
Eprint ID
33208
Cite as
Beierlein, L. , Nehrke, G. and Brey, T. (2012): Confocal Raman microscopy and its contribution to sclerochronology , Jubiläumstagung der Paläontologischen Gesellschaft, Berlin, Germany, 24 September 2012 - 29 September 2012 .


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