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Repeta, DJ, Quan TM, Aluwihare LI, Accardi AM.  2002.  Chemical characterization of high molecular weight dissolved organic matter in fresh and marine waters. Geochimica Et Cosmochimica Acta. 66:955-962.   10.1016/s0016-7037(01)00830-4   AbstractWebsite

The high molecular weight fraction of dissolved organic matter in a suite of takes, rivers, seawater, and marine sediment interstitial water samples was collected by ultrafiltration and characterized by molecular level and spectroscopic techniques. Proton nuclear magnetic resonance spectra of all samples show a high degree of similarity, with major contributions from carbohydrates, bound acetate, and lipids. Molecular level analyses of neutral sugars show seven monosaccharides, rhamnose, fucose, arabinose, xylose, mannose, glucose, and galactose, to be abundant, and to occur in comparable relative amounts in each sample. Previous studies have emphasized the distinctive composition of dissolved humic substances in fresh and marine waters, and have attributed these differences to sources and transformations of organic matter unique to each environment. In contrast we find a large fraction of freshwater high molecular weight dissolved organic matter (HMWDOM; > 1 kD) to be indistinguishable from marine HMWDOM in bulk and molecular-level chemical properties. Aquatic HMWDOM is similar in chemical composition to biologically derived acylated heteropolysaccharides isolated from marine algal cultures, suggesting a biological source for some fraction of persistent HMWDOM. High molecular weight DOC contributes 51 +/- 26% of the total DOC, and monosaccharides 18 +/- 8% of the total HMWDOC in our freshwater samples. These contributions are on average higher and more variable, but not significantly different than for surface seawater (30% and 16% respectively), Biogeochemical processes that produce, accumulate, and recycle DOM may therefore share important similarities and be broadly comparable across a range of environmental settings. Copyright (C) 2002 Elsevier Science Ltd.

Repeta, DJ, Aluwihare LI.  2006.  Radiocarbon analysis of neutral sugars in high-molecular-weight dissolved organic carbon: Implications for organic carbon cycling. Limnology and Oceanography. 51:1045-1053. AbstractWebsite

We used compound-specific natural-abundance radiocarbon analyses of neutral sugars to study carbon cycling of high-molecular-weight (HMW) dissolved organic carbon (DOC) at two sites in the North Pacific Ocean. Sugars released from HMW DOC by acid hydrolysis were purified by high-pressure liquid chromatography and analyzed for radiocarbon content via accelerator mass spectrometry. The seven most abundant sugars recovered from HMW DOC have similar radiocarbon values, supporting the hypothesis that these sugars are incorporated into a common family of polysaccharides. Neutral sugar /\14C values from surface waters collected in 1999 and 2001 are 89 ± 13%o and 57 ± 6%o, respectively; these values are much more enriched in radiocarbon than those found in previous studies that used operationally defined carbohydrate fractions. Radiocarbon values for HMW DOC neutral sugars are the same as, or only slightly depleted relative to, dissolved inorganic carbon (DIC), which is consistent with rapid cycling and a short (<3-yr) residence time. In addition, the /\14C value of neutral sugars at 600 m is 20%o enriched relative to DIC /\14C, suggesting that a fraction of dissolved neutral sugars at this depth are introduced by dissolution from large, rapidly sinking particles.