Linking variations in DOM composition and the microbial community in the water masses of the deep northeast Atlantic Ocean

Dissolved organic matter (DOM) and microbial communities in the marine environment are inherently linked as microbes consume, produce, and transform dissolved compounds that contribute to the DOM pool. Thus, we might expect the composition of DOM and characteristics of the microbial community to co-vary throughout the water column. However, portions of the DOM pool cycle on varying timescales, ranging from hours to millennia, and the lability and residence times of these fractions may be reflected in their relationship to the dynamics of the in situ microbial community. To explore these associations, we analyzed several components of DOM of various water masses throughout the deep northeast Atlantic Ocean, including the molecular composition of solid phase extracted (SPE) DOM using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and the distribution of dissolved free (DFAA) and total hydrolyzable amino acids (THAA). While SPE-DOM as analyzed by FT-ICR-MS appears to be generally a conservative parameter in northeast Atlantic deep water, other components of the DOM pool vary with depth and latitude similar to changes in the microbial community. For example, DFAA show a more water mass specific distribution, and the relative mol% of the organic acid taurine is increased in subsurface (100 m) samples. Here we demonstrate variability among different fractions of marine DOM by assessing its composition in the deep northeast Atlantic Ocean in the context of microbial abundance, metabolic activity, and community composition.