[Department of Ocean Science] PhD Thesis Defense Seminar: Using ultra-high-resolution mass spectrometry and data-driven techniques to study dissolved organic matter cycling in estuarine and marine environments

Abstract: 

Dissolved organic matter (DOM) is one of the largest reactive carbon pools in the ocean and its cycling is closely linked with global climate change. With the widespread application of ultra-high-resolution mass spectrometry and advancements in more recently upgraded techniques, complex, high-dimensional, and highly heterogeneous molecular fingerprint datasets have been generated and accumulated. Traditional statistical and analytical approaches struggle to handle such datasets, hindering our further understanding of DOM cycling. In this dissertation, we demonstrate the promising and comprehensive applications of data-driven approaches in helping to determine the molecular composition of DOM at compositional, isomeric, and structural dimensions. These characterizations contribute to elucidating several critical processes of DOM over the land-to-ocean continuum, including evaluating the effect of biotic and abiotic degradation on DOM, elucidating the nature and flux of terrestrial-derived DOM transported to the ocean, and examining the major hypotheses accounting for the long-term stability of oceanic recalcitrant DOM. Results revealed that on the one hand, photochemical degradation significantly alters the terrestrial DOM in estuaries and potentially influences the oceanic carbon sink, while the hidden isomeric diversity links terrestrial OM export to persistent oceanic carbon. On the other hand, either the inherent structure or dilution hypothesis may not fully account for the persistence of oceanic recalcitrant DOM. This work highlights the immense potential of data-driven approaches and advanced ultra-high-resolution mass spectrometry in exploring marine biogeochemistry.