Conservation of dissolved organic matter molecular composition during mixing of the deep water masses of the northeast Atlantic Ocean

Characterizing the composition ofmarine dissolved organicmatter (DOM) is important for gaining insight into itsrole in oceanic biogeochemical cycles. Using Fourier transform ion cyclotron resonance mass spectrometry, weanalyzed the molecular composition of solid phase extracted (SPE) DOM from the northeast Atlantic to investigatethe specificity of the DOMpool of the individualmajor watermasses of the North Atlantic. All 272 measuredsamples from depths ranging from 87 to 5609 m and latitudes from 24°N to 68°N shared 96% similarity (on aBray–Curtis scale) in their DOM composition. Small variations between subsurface and deep samples andamong latitudinal groupings were identified, but overall, water mass specific SPE-DOM composition was notapparent. A strong correlation between a calculated degradation index and water mass age indicates variabilityin portions of the DOM pool, and ocean-scale differences were observed between the North Atlantic and deepNorth Pacific. However, within the deep northeast Atlantic, conservative mixing primarily drives the molecularcomposition of SPE-DOM