Natural organic matter (NOM) consists of a complex and heterogeneous mixture of naturally occurring compounds that are involved in many important biogeochemical processes such as metal complexation, pollutant fate and transport, nutrient cycling, redox reactions and also acts as a source of energy for the microbial community.  The observed structural heterogeneity of NOM, in terms of molecular formulae, encodes (i) source materials, (ii) transforming processes and (iii) their controlling environmental and biological factors. It is therefore necessary to better understand and identify the underlying processes that control organic matter dynamics.

Biogeochemical studies conducted at the molecular-level have significantly improved our understanding of carbon dynamics and highlighted the importance of high resolution analytical techniques in biogeochemical sciences. High (or Ultrahigh) resolution mass spectrometry (MS) techniques (like Fourier-transform Orbitrap MS  or  Fourier-transform ion cyclotron resonance MS) coupled to soft ionization techniques now allow the identification of thousands of intact individual molecular formulae from complex mixtures like dissolved organic matter (DOM).  

This seminar will present two recent applications of high resolution mass spectrometry applied to biogeochemical studies.

• the first example will focus on the molecular composition of DOM from the podzol soils of a temperate Pine forest (forêt des Landes de Gascogne)[1]. The objectives of this study were to assess the changes in molecular diversity of DOM moving vertically along a soil profile, through the upper and the accumulation horizons of the sandy permeable podzol toward the aquifer of a maritime pine forest in western France.

• the second example will focus on the characterization of atmospheric organic matter in the cloud aqueous phase at the puy de Dôme station, and its temporal variation with respect to the cloud’s physicochemical parameters, to demonstrate that cloud DOM composition contains integral information on emission sources and processes[2]^,[3],[4].