Spectroscopic characterization of oceanic dissolved organic matter isolated by reverse osmosis coupled with electrodialysis

Abstract

a b s t r a c tOceanic dissolved organic matter (DOM) is one of the largest pools of reduced carbon on Earth, yet DOM remains poorly chemically characterized. Studies to determine the chemical nature of oceanic DOM have been impeded by the lack of efficient and non-fractioning methods to recover oceanic DOM. Here, a DOM fraction (~40 to 86% recovery) was isolated using reverse osmosis/electrodialysis (RO/ED) and analyzed by solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. Samples were obtained from biogeochemically distinct environments: photobleached surface gyre, productive coastal upwelling zone, oxygen minimum, North Atlantic Deep Water, and North Pacific Deep Water. A ubiquitous 'background' refractory carbon pool was apparent throughout the ocean and dominated in the deep Pacific Ocean. Advanced NMR spectral editing revealed that condensed aromatic and quaternary anomeric carbons contribute to this deep refractory DOC pool, the quaternary anomeric carbons being a newly identified and potentially important component of bio-refractory carbohydrate-like carbon. Additionally, our results support the multi-pool (e.g. 3-pool: labile, semi-labile, and refractory) conceptual model of marine DOM biogeochemistry. Surface samples, hypothesized to be enriched in labile and semilabile DOM, were enriched in carbohydrate-like material consistent with prior studies. High carboxyl signals in the deep Pacific support the hypothesis that a major fraction of the refractory pool consists of carboxyl-rich alicyclic molecules (CRAM).

Composition of Dissolved Organic Matter in Pore Waters of Anoxic Marine Sediments Analyzed by 1H Nuclear Magnetic Resonance Spectroscopy

“…Differences between HMW-and SPE-DOM are less obvious for deep-sea DOM (Hertkorn et al, 2006(Hertkorn et al, , 2013, consistent with the semi-labile nature of APS/HPS. Relative to ultrafiltration and SPE, RO/ED has been reported to recover a larger and more representative fraction of total DOM (Vetter et al, 2007;Gurtler et al, 2008;Koprivnjak et al, 2009;Green et al, 2014;Helms et al, 2015), but the large sample volume requirement makes RO/ED unsuitable for the study of DOM in pore waters. A mini-electrodialysis system designed to handle small-volume samples has been developed, but appears to cause considerable DOC contamination (Chen et al, 2011).…”

Chemical Characterization and Cycling of Dissolved Organic Matter

“…Combined neutral sugar distributions of semi-labile DOM and foam are also similar (Gogou and Repeta, 2010). 1 H NMR and 13 C NMR spectra of DOM collected by ultrafiltration, SPE, and ED/RO all show resonances assigned to semi-labile DOM carbohydrate as deep as 5200 m, but further chemical and isotopic characterization is needed to link surface and deep reservoirs of semi-labile DOM (Benner et al, 1992;Helms et al, 2013;Quan and Repeta, 2007;Sannigrahi et al, 2005).…”

“…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).…”

Characterizing CDOM Spectral Variability Across Diverse Regions and Spectral Ranges

“…Few studies have reported spectral slope from 350 to 550 nm to our knowledge (Hancke et al, 2014;Kowalczuk et al, 2006), making it difficult to directly assess what S G350:550 estimates about CDOM composition. We propose that S E350:400 is a better metric for tracking compositional changes in the CDOM pool affiliated with photodegradation and in situ production of CDOM as suggested by Helms et al (2015Helms et al ( , 2013. However, S G350:550 displayed greater uniqueness between provinces, while S E350:400 displayed more consistent trends with depth across all spectral ranges.…”