Bacterial reworking of dissolved organic matter in the deep Arctic Ocean: influence of its chemical composition

The microbial transformation of dissolved organic matter (DOM) is crucial for a better understanding of its dynamics in the ocean. In controlled laboratory incubations (20 days), we assessed the optical and molecular changes in the DOM pool to discern how the same bacterial community processes DOM collected in four distinct water masses of the Canada Basin, Arctic Ocean (i.e, Pacific Winter Water, Atlantic Halocline, Atlantic Water - Barents Sea Strait branch, and deep temperature minimum). While all water masses contained the same fluorescent components, they underwent unique processing when in contact with the microbial community. These results suggest that the makeup of a particular fluorescent component probably varied between different water layers. The molecular characteristics measured with a trapped ion mobility spectrometer coupled with a time-of-flight mass spectrometer (TIMS-TOF) and an electrospray ionization source (positive ionization mode) revealed distinct molecular features in the solid-phase extracts of DOM between the water masses, and the number of those features increased by the end of the incubation period. The number of common molecular features was also greater in contiguous water masses, likely a result of water mass mixing. Spearman's rank correlations between fluorescence characteristics and TIMS-TOF features were used to establish the connections between DOM and molecular formulas. 34% of the common TIMS TOF features were associated with at least one PARAFAC component. Overall, these findings indicate that the refractory character of deep DOM is contingent upon its intrinsic assemblage.

Presentation Preference: Oral

Primary Presenter: Celine Gueguen, Universite de Sherbrooke (celine.gueguen@usherbrooke.ca)

Authors:

Nicolas Sylvestre, Universite de Sherbrooke  (nicolas.sylvestre2@usherbrooke.ca)