High-field NMR spectroscopy and FTICR mass spectrometry: Powerful discovery tools for the molecular level characterization of marine dissolved organic matter.

• Published in: Biogeosciences
• Main Authors: Hertkorn, N., Harir, M., Koch, B.P., Michalke, B., Schmitt-Kopplin, P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Gesellschaft Mbh 2013
• Subjects: Antarctic; Antarc*; NADW; North Atlantic Deep Water; North Atlantic; South Atlantic Ocean
• Online Access: https://push-zb.helmholtz-muenchen.de/frontdoor.php?source_opus=24464; https://doi.org/10.5194/bg-10-1583-2013

High-performance, non-target, high-resolution organic structural spectroscopy was applied to solid phase extracted marine dissolved organic matter (SPE-DOM) isolated from four different depths in the open South Atlantic Ocean off the Angola coast (3 degrees E, 18 degrees S; Angola Basin) and provided molecular level information with extraordinary coverage and resolution. Sampling was performed at depths of 5 m (Angola Current; near-surface photic zone), 48 m (Angola Current; fluorescence maximum), 200 m (still above Antarctic Intermediate Water, AAIW; upper mesopelagic zone) and 5446 m (North Atlantic Deep Water, NADW; abyssopelagic, similar to 30 m above seafloor) and produced SPE-DOM with near 40% carbon yield and beneficial nuclear magnetic resonance (NMR) relaxation properties, a crucial prerequisite for the acquisition of NMR spectra with excellent resolution. H-1 and C-13 NMR spectra of all four marine SPE-DOM showed smooth bulk envelopes, reflecting intrinsic averaging from massive signal overlap, with a few percent of visibly resolved signatures and variable abundances for all major chemical environments. The abundance of singly oxygenated aliphatics and acetate derivatives in H-1 NMR spectra declined from surface to deep marine SPE-DOM, whereas C-based aliphatics and carboxyl-rich alicyclic molecules (CRAM) increased in abundance. Surface SPE-DOM contained fewer methyl esters than all other samples, likely a consequence of direct exposure to sunlight. Integration of C-13 NMR spectra revealed continual increase of carboxylic acids and ketones from surface to depth, reflecting a progressive oxygenation, with concomitant decline of carbohydrate-related substructures. Aliphatic branching increased with depth, whereas the fraction of oxygenated aliphatics declined for methine, methylene and methyl carbon. Lipids in the oldest SPE-DOM at 5446 m showed a larger share of ethyl groups and methylene carbon than observed in the other samples. Two-dimensional NMR spectra showed exceptional resolution and depicted ...