Chesapeake Biological Laboratory,University of Maryland Center for Environmental Science

I am a biogeochemists with an interest in the molecular diversity of complex organic matrices in aquatic environments analyzed by modern analytical technology. Broad scale fingerprinting of complex dissolved organic matter (DOM) has enabled to shed light on the chemodiversity of this material in diverse aquatic systems.

My major focus has been the marine carbon cycle, but also freshwater and engineered systems. I have been using primarily tools to determine the optical properties (absorbance, fluorescence) and the molecular composition (ultrahigh resolution mass spectrometry) of DOM. I also have a strong interest in the reactivity of DOM and in particular its photochemical degradation in aquatic systems. We recently developed a unique photo-degradation system, which is used to determine the time-resolved fate of chromophores in DOM under strictly controlled pH conditions and results indicated a strong pH dependency, which is dependent on the origin of DOM.



Photochemistry of Marine Dissolved Organic Matter

The link between detailed molecular characterization of marine dissolved organic matter analyzed by ultrahigh resolution mass spectrometry and its optical properties is only slowly emerging and this seminar will give an overview about what we know about the molecular composition of light absorbing chromophoric DOM (CDOM) in the World’s Oceans with a specific focus on how semi-continuous excitation emission matrix fluorescence monitoring can be used to determine photo-degradation kinetic data. CDOM is increasing with depth in the open ocean but the origin of this material is still under debate with suggested sources coming either from terrestrially-derived polyphenols or in situ production from marine autotrophs or heterotrophs. Fluorescence has been particularly useful due to its sensitivity and Parallel Factor Analysis (PARAFAC) statical modelling has advanced the field to describe different fluorescence components that were associated with different fluorophore groups. A strong correlation of fluorescence signals with the apparent oxygen utilization (AOU) in the Pacific suggested an in situ production of fluorophores, but recent results showed that this correlation is not apparent in the Atlantic. A critical discussion about potential sources of marine CDOM will also be part of this seminar.