USING RAMAN MICROSCOPY FOR IDENTIFICATION AND SOURCING OF WOODY DEBRIS IN MARINE SEDIMENTS

Burial of terrestrial organic carbon in marine sediments constitutes an important carbon sink. Terrestrial organic carbon is buried in both fine-grained sediments and in coarser particulates such as plant and woody fragments which are transported by rivers into the oceans. Species and source identification of woody debris preserved in marine sediments can inform transport processes and aid in vegetation cover and climate reconstructions. We used a confocal Raman microscope with a 785-nm near-IR laser system to identify woody debris preserved in marine sediments. First, we irradiated modern angiosperm and gymnosperm wood samples and created a spectral library. Different wood species produced similar spectral with bands attributed to lignin (1,550 – 1,640 cm-1) and cellulose (1,090–1,105 cm-1) but with different intensities. Additional spectral features related to the distribution of carbohydrates, occurrence of aromatic C-C double bonds, and C-H bond stretching, can be used to identify different species. For example, bamboo samples show a prominent peak at 1172 cm-1 which is completely absent from giant sequoia samples and possibly other gymnosperms. Samples of woody debris preserved in marine sediments have a more muted spectra than modern wood, but still allow identification of lignin/cellulose and therefore may also indicate the preservation state of the sample. Results from this study suggest that Raman microscopy is a promising tool to identify wood species in marine sediments.