PhD defence: Nanna Bjerregaard Pedersen

Nanna Bjerregaard Pedersen defends PhD her thesis: Microscopic and spectroscopic characterisation of waterlogged archaeological softwood from anoxic environments

Principal Supervisor
Professor Claus Felby
Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

 Co-supervisor
Senior Researcher Lisbeth Garbrecht Thygesen
Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Co-supervisor
Senior Researcher Poul Jensen
National Museum of Denmark, Copenhagen, DK

Co-supervisor
Professor Charlotte Gjelstrup Björdal
Department of Conservation, University of Gothenburg, Sweden

Assessment Committee
Senior Researcher Søren Barsberg (chair)
Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen, DK

Professor David Gregory
National Museum of Denmark, Copenhagen, DK

Senior Researcher Gry Alfredsen
Norwegian Forest and Landscape Institute, Ås, Norway

Summary
Confocal Raman imaging, UV-microspectrophotometry, light microscopy, transmission electron microscopy, compositional analysis, and ATR-FTIR spectroscopy has been applied to waterlogged archaeological Norway spruce [Picea abies (L.) Karst] and Scots pine [Pinus sylvestris L.] retrieved from anoxic waterlogged sites and solely decayed by erosion bacteria to refine the understanding of the residual wood structure left after degradation. This was done not only to improve the ability to develop suitable and cost effective conservations treatments but also to improve the understanding of anaerobic decay mechanisms acting on plant biomass in waterlogged anoxic environment.Morphological analyses showed typical erosion bacteria decay patterns in the residual wood structure. Decay resistance of some cell types and cell wall compartments in preference to others is most likely explained not only by elevated lignin content but also by differences in chemical composition and supramolecular structure of the biopolymers in the cell wall. Spatially resolved chemical information showed that the residual material always contained lignin or lignin-like substances and that the lignin concentration varied from levels lower than to levels higher than native S2 layer concentrations. The residual material showed strong depletion of carbohydrates. The chemical composition of the lignin in the residual material was similar to the sound waterlogged S2 layer. However, an initial size exclusion chromatography analysis points toward partial depolymerisation of the lignin polymer in the residual material. The overall analyses show a high degree of lignin conservation in the residual wood structure and points to the theory that the lignin substances in the residual material most likely form a gel-like structure with embedded lignin aggregates with higher lignin content. Chemical analysis showed evidence for abiotic hydrolysis of acetyl groups in glucomannan and ester bonds in lignin-carbohydrate complexes and minor abiotic oxidation of the lignin polymer.

After the PhD defence there will be a reception on Rolighedsvej 23, in the canteen in the new building.  All are welcome.