Recent advances in infrared spectroscopy applied to single specimen dinoflagellate cysts: methodological framework and applications

Fourier-transformed infrared (FTIR) spectroscopy is a spectrochemical technique able to retrieve macromolecular information from organic materials. When combined with a microscope (micro-FTIR), the (geo)chemical composition of single specimen dinoflagellate cysts (dinocysts) can be determined. Over the last decades a small number of dinocyst micro-FTIR studies booked often inconsistent results by overlooking important methodological aspects during analysis. This study takes into account variables like sample preparation, specimen morphology and size and spectral data processing steps and presents a standardized method based on attenuated total reflectance (ATR) micro-FTIR spectroscopy which is able to collect robust spectral datasets. These datasets are largely devoid of nonchemical artifacts inherent to other infrared spectrochemical methods which have typically been used in similar studies in the past (i.e. transmission and transflection spectroscopy). Several guidelines are proposed which facilitate the collection and qualitative interpretation of highly reproducible and repeatable spectrochemical dinocyst data. These, in turn, pave the way for a systematic exploration of dinocyst chemistry and its assessment as a chemotaxonomical tool or proxy. An ATR micro-FTIR case study on morphologically similar late Paleogene to early Neogene dinocysts Palaeocystodinium golzowense, Svalbardella clausii and Svalbardella cooksoniae is also presented, which highlights the chemotaxonomical potential of the method.