Recalcitrant Dissolved Organic Carbon Fractions

Hansell, Dennis A.

doi:10.1146/annurev-marine-120710-100757

Cited by 683 publications

(838 citation statements)

References 131 publications

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“…More recently, the transformation of biologically labile organic matter into refractory (long lifetime in the dark ocean) 2 compounds by prokaryotic activity has been termed the 'microbial carbon pump' and may also constitute an effective mechanism to accumulate reduced carbon in the dark ocean 3,4 . Given the large pool of refractory DOM (RDOM) in the oceans (B656 pg C) 2 , understanding its generation, transformation and role in carbon sequestration is crucial in regards to understanding present and future CO 2 emission scenarios.…”

mentioning

confidence: 99%

Turnover time of fluorescent dissolved organic matter in the dark global ocean

et al. 2015

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Marine dissolved organic matter (DOM) is one of the largest reservoirs of reduced carbon on Earth. In the dark ocean (4200 m), most of this carbon is refractory DOM. This refractory DOM, largely produced during microbial mineralization of organic matter, includes humic-like substances generated in situ and detectable by fluorescence spectroscopy. Here we show two ubiquitous humic-like fluorophores with turnover times of 435 ± 41 and 610 ± 55 years, which persist significantly longer than the B350 years that the dark global ocean takes to renew. In parallel, decay of a tyrosine-like fluorophore with a turnover time of 379 ± 103 years is also detected. We propose the use of DOM fluorescence to study the cycling of resistant DOM that is preserved at centennial timescales and could represent a mechanism of carbon sequestration (humic-like fraction) and the decaying DOM injected into the dark global ocean, where it decreases at centennial timescales (tyrosine-like fraction).

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confidence: 99%

Turnover time of fluorescent dissolved organic matter in the dark global ocean

et al. 2015

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“…Goldberg et al, 2011;Kaiser and Benner, 2012) or via experimental degradation approaches (e.g., Gruber et al, 2006;Kawasaki and Benner, 2006;Davis et al, 2009). The spatiotemporal variability of biomolecules and net removal rates of DOC or distinct fractions (e.g., Amon and Benner, 1994;Loh et al, 2004;Kaiser and Benner, 2009;Hansell, 2013) corroborated the concepts of age-, size-and reactivity continua in which the microbial carbon pump (Jiao et al, 2010) plays a major role in transforming fresh into refractory organic matter. As a result of the global thermohaline circulation pattern, deep water masses are exchanged on a millennial time scale.…”

Section: Introductionmentioning

confidence: 65%

“…First order kinetics imply that the degradation rate is proportional to DOC concentration. It is common practice to account for an exponential rate-law by distinguishing between labile DOC with the highest removal rate, followed by semi-labile DOC with the second largest rate and so on (Hansell, 2013). However, these discrete and operationally defined fractions contrast with the concepts of size or age reactivity continua as proposed by e.g., Amon and Benner (1996) and Walker et al (2011).…”

Section: Degradation Rate Of Bulk Doc Modeled From Spe-dom D 14 Cmentioning

confidence: 99%

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

Lechtenfeld

Kattner

Flerus

et al. 2014

Geochimica et Cosmochimica Acta

276

259

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More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000-6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50°N to 70°S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising D 14 C values from À229& to À495&) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment ("island of stability"). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 lM) while the organic radiocarbon was significantly more depleted than that of the East Atlantic, representing average surface water DOM ages of 4920 ± 180 a. These results are in accordance with a highly degraded DOM in the Weddell Sea surface water as also shown by the molecular degradation index I DEG obtained from FT-ICR MS data. Further, we identified 339 molecular formulae which probably contribute to an increased DOC concentration in the Southern Ocean and potentially reflect an accumulation or enhanced sequestration of refractory DOC in the Weddell Sea. These results will contribute to a better understanding of the persistent nature of marine DOM and its role as an oceanic carbon buffer in a changing climate.

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“…Although cyanobacterial hydrocarbons are only a small proportion (0.00032%) of the estimated 662 billion tons of dissolved organic carbon (DOC) present in the ocean at any point in time (47), only a relatively small fraction of this bulk DOC (∼0.2 billion tons) is turned over within days (48). Cyanobacterial hydrocarbons, with an estimated pool of 2.12 million tons, likely belong to the labile subset of rapidly cycled DOC and constitute a notable proportion (∼1%) of that bioavailable fraction.…”

Section: Cyanobacterial Hydrocarbon Production Can Support Populationmentioning

confidence: 99%

Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle

Lea‐Smith

Biller

Davey

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

174

122

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Hydrocarbons are ubiquitous in the ocean, where alkanes such as pentadecane and heptadecane can be found even in waters minimally polluted with crude oil. Populations of hydrocarbon-degrading bacteria, which are responsible for the turnover of these compounds, are also found throughout marine systems, including in unpolluted waters. These observations suggest the existence of an unknown and widespread source of hydrocarbons in the oceans. Here, we report that strains of the two most abundant marine cyanobacteria, Prochlorococcus and Synechococcus, produce and accumulate hydrocarbons, predominantly C15 and C17 alkanes, between 0.022 and 0.368% of dry cell weight. Based on global population sizes and turnover rates, we estimate that these species have the capacity to produce 2-540 pg alkanes per mL per day, which translates into a global ocean yield of ∼308-771 million tons of hydrocarbons annually. We also demonstrate that both obligate and facultative marine hydrocarbon-degrading bacteria can consume cyanobacterial alkanes, which likely prevents these hydrocarbons from accumulating in the environment. Our findings implicate cyanobacteria and hydrocarbon degraders as key players in a notable internal hydrocarbon cycle within the upper ocean, where alkanes are continually produced and subsequently consumed within days. Furthermore we show that cyanobacterial alkane production is likely sufficient to sustain populations of hydrocarbon-degrading bacteria, whose abundances can rapidly expand upon localized release of crude oil from natural seepage and human activities.cyanobacteria | hydrocarbons | hydrocarbon cycle | hydrocarbon-degrading bacteria | oil remediation

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Recalcitrant Dissolved Organic Carbon Fractions

Cited by 683 publications

References 131 publications

Turnover time of fluorescent dissolved organic matter in the dark global ocean

Turnover time of fluorescent dissolved organic matter in the dark global ocean

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle

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