PNNL

Abstract

Marine dissolved organic matter (DOM) contains a highly complex mixture of structurally diverse small molecules that elude rapid biological degradation. Spatial and temporal variations in the abundance of DOM reflect the existence of fractions that are removed from the water column over different timescales, ranging from seconds to millennia. However, it remains unknown whether the intrinsic chemical properties of these organic components affect their persistence. Here, we developed a novel analytical approach to elucidate the molecular composition of distinct DOM fractions along a water column in the North Atlantic Gyre, and we relate the compositional differences of the fractions to their persistence. Our analysis utilizes state-of-the-art ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry at 21 Tesla coupled to liquid chromatography and a scalable data informatics pipeline developed in CoreMS. The pipeline was used to generate rigorous molecular formula assignments to mass peaks, provide internal-standard based quality control metrics on quantitation, and perform data alignment, blank subtraction, and hierarchical clustering. Clustering analysis binned 6740 distinct molecular components into groups that correspond to the depth distribution of semi-labile, semi-refractory, and refractory fractions of dissolved organic carbon. The labile fractions, which were concentrated near the ocean surface, contained more aliphatic, reduced, and isomerically well-defined molecules than the refractory fractions, which occurred uniformly throughout the water column. These molecular properties are consistent with lower aqueous solubility of more labile DOM fractions, which may promote faster removal by sorption to particles.