Abstract:

Oceanic recalcitrant dissolved organic matter (RDOM) represents a tremendous and long-lived carbon reservoir that potentially mitigates global climate change. Yet the reasons behind the long-term stability of RDOM have been debated for years. Two major hypotheses have been proposed to address the paradox of RDOM persistence in the ocean. The inherent stability hypothesis connects the DOM reactivity to the molecular structure, suggesting that the persisting molecules have intrinsic recalcitrant structures that prevent degradation. Alternatively, the dilution hypothesis, also known as the molecular diversity hypothesis, proposes that the persistence of DOM is due to the extremely low concentrations of each individual DOM molecule. As such, the decomposition rate of an organic substrate is influenced by concentration, and the diluted nature of DOM contributes to its persistence. While some evidence supports either the intrinsic stability or dilution hypotheses, neither has been conclusively proven so far. Understanding the isomeric diversity of DOM matters in determining which mechanism primarily controls its long-term stability, but this aspect remains to be investigated.

Recent advances in analytical techniques and data analysis strategies have provided new perspectives for reinvestigating this issue. In this talk, I will share our investigation that combines multiple ultra-high-resolution mass spectrometry techniques with molecular networking tools and machine learning models. I will present the isomeric diversity of DOM molecules from Chinese estuaries and a water column in the South China Sea, and discuss its implications for understanding the long-term stability of RDOM.

Additionally, I will provide a brief overview of my other data-driven research efforts aiming to elucidate the cycling of natural organic matter.