High field NMR spectroscopy and FTICR mass spectrometry: powerful discovery tools for the molecular level characterization of marine dissolved organic matter from the South Atlantic Ocean

Abstract

Non target high resolution organic structural spectroscopy of marine dissolved organic matter (DOM) isolated on 27 November 2008 by means of solid phase extraction (SPE) from four different depths in the South Atlantic Ocean off the Angola coast (3.1° E; −17.7° S; Angola basin) provided molecular level information of complex unknowns with unprecedented coverage and resolution. The sampling was intended to represent major characteristic oceanic regimes of general significance: 5 m (FISH; near surface photic zone), 48 m (FMAX; fluorescence maximum), 200 m (upper mesopelagic zone) and 5446 m (30 m above ground). <br><br> 800 MHz proton (<sup>1</sup>H) nuclear magnetic resonance (NMR) <sup>1</sup>H NMR, spectra were least affected by fast and differential transverse NMR relaxation and produced at first similar looking, rather smooth bulk NMR envelopes reflecting intrinsic averaging from massive signal overlap. Visibly resolved NMR signatures were most abundant in surface DOM but contributed at most a few percent to the total <sup>1</sup>H NMR integral and were mainly limited to unsaturated and singly oxygenated carbon chemical environments. The relative abundance and variance of resolved signatures between samples was maximal in the aromatic region; in particular, the aromatic resolved NMR signature of the deep ocean sample at 5446 m was considerably different from that of all other samples. When scaled to equal total NMR integral, <sup>1</sup>H NMR spectra of the four marine DOM samples revealed considerable variance in abundance for all major chemical environments across the entire range of chemical shift. Abundance of singly oxygenated CH units and acetate derivatives declined from surface to depth whereas aliphatics and carboxyl-rich alicyclic molecules (CRAM) derived molecules increased in abundance. Surface DOM contained a remarkably lesser abundance of methyl esters than all other marine DOM, likely a consequence of photodegradation from direct exposure to sunlight. <br><br> All DOM showed similar overall <sup>13</sup>C NMR resonance envelopes typical of an intricate mixture of natural organic matter with noticeable peaks of anomerics and C-aromatics carbon whereas oxygenated aromatics and ketones were of too low abundance to result in noticeable humps at the S/N ratio provided. Integration according to major substructure regimes revealed continual increase of carboxylic acids and ketones from surface to deep marine DOM, reflecting a progressive oxygenation of marine DOM, with concomitant decline of carbohydrate-related substructures. <br><br> Isolation of marine DOM by means of SPE likely discriminated against carbohydrates but produced materials with beneficial NMR relaxation properties: a substantial fraction of dissolved organic molecules present allowed the acquisition of two-dimensional NMR spectra with exceptional resolution. JRES, COSY and HMBC NMR spectra were capable to depict resolved molecular signatures...

Dissolved organic matter in sea spray: a transfer study from marine surface water to aerosols

“…To verify this natural fractionation process, we selected a particular sampling point in the Angola Basin (27 November 2008 at 3.1 • E, 17.7 • S), in which surface water has been also studied in great detail by NMR spectroscopy and FT-ICR MS mass spectrometry (Hertkorn et al, 2012). The surface water layer and the aerosols of this sampling site were characteristic of pristine open ocean (Fig.…”

“…The selected day sample for surface water, sea spray generation and day aerosol was chosen at the Angola Basin (27 November 2008 at 3.1 • E, 17.7 • S), i.e. at the same location in which NOM in surface water has been characterized in great detail (Hertkorn et al, 2012). During the expedition, no heavy rain showers occurred in the Intertropical Convergence Zone (ITCZ), although intense rainfall is common in this region; thus the collection of surface water with the fish sampler generated representative surface water for analysis and for the production of burst in the laboratory on board (Fig.…”

“…Own recent results show that the regional qualitative variations in dissolved organic carbon (DOC) composition found in the surface water corresponded roughly to Longhurst ecological provinces of the sea (Longhurst, 2007) and were, in addition, partially reflected in Biogeosciences, 9, 1571-1582, 2012 www.biogeosciences.net/9/1571/2012/ the aerosols released (work in progress, Koch and Kattner, 2012;Schmitt-Kopplin, 2012). We showed, in this study specifically on one specific site as well as on average across all the data of the cruise, that these compounds were preferentially concentrated in aerosols with a specific N-and Spartitioning and contribute largely to the formation of primary organic aerosols (POA) in the atmosphere.…”

Chemical Characterization and Cycling of Dissolved Organic Matter

“…The processes that lead to the formation and removal of SPE-DOM in the ocean are not known, but high-field NMR and high-resolution MS have added unprecedented detail to our knowledge of its composition (Dittmar and Koch, 2006;Helms et al, 2013;Hertkorn et al, 2006Hertkorn et al, , 2012. 1 H NMR spectra are characterized by broad peaks between 0.8 and 10 ppm with substantial signal overlap (Figure 2.10).…”

Spectroscopic detection of a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean

“…Its absorption and fluorescence characteristics fit more to a non-chlorin porphyrin molecule. We tried to identify target structures and molecular formulas in the data sets for this issue (Flerus et al, 2012;Hertkorn et al, 2012). Although Hertkorn et al identified nitrogen heterocycles which might be related to a porphyrin, its molecular identification is still subject to ongoing research.…”