<sup>14</sup>C Background Levels in An Accelerator Mass Spectrometry System

Vogel, John S.; Nelson, D. E.; Southon, John

doi:10.1017/s0033822200043733

Cited by 280 publications

(189 citation statements)

References 8 publications

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“…The CO 2 was subsequently reduced with H 2 to graphite over a Co catalyst (Vogel et al, 1987). Graphite targets were analyzed for 14 C at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory.…”

Section: C Measurementsmentioning

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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Section: C Measurementsmentioning

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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“…The CO2 evolved from carbonates and organics was purified cryogenically, then reduced to graphite using the cobalt-catalyzed reduction method described in VOGEl, et al (1987). Graphite targets were run at the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory (DAvis et al, 1990).…”

Section: Sediment Collection and Analysismentioning

confidence: 99%

Carbon budget for the mid-slope depocenter of the Middle Atlantic Bight

Anderson

Rowe

Kemp

et al. 1994

Deep Sea Research Part II: Topical Studies in Oceanography

170

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Abstract--A mass budget was constructed for organic carbon on the upper slope of the Middle Atlantic Bight, a region thought to serve as a depocenter for fine-grained material exported from the adjacent shelf. Various components of the budget are internally consistent, and observed differences can be attributed to natural spatial variability or to the different time scales over which measurements were made. The flux of organic carbon to the sediments in the core of the depocenter zone, at a water depth of -1000 nr, was measured with sediment traps to be -65 mg C m 2 day 1, of which 6-24 mg C m 2 day ~ is buried. Oxygen fluxes into the sediments, measured with incubation chambers attached to a free vehicle lander, correspond to total carbon remineralization rates of 49-70 mg C in 2 day-1. Carbon remineralization rates estimated from gradients of Corg within the mixed layer, and from gradients of dissolved ammonia and phosphate in pore waters, sum to only -4-6 mg C m -2 day i. Most of the Q,,.g remineralization in slope sediments is mediated by bacteria and takes place within a few mm of the sediment-water interface.Most of the Corg deposited on the upper slope sediments is supplied by lateral transport from other regions, but even if all of this material were derived from the adjacent shelf, it represents <2% of the mean annual shelf productivity. This value is further lowered by recognizing that as much as half of the C,,rg deposited on the slope is refractory, having originated by reworking from older deposits. Refractory Corg arrives at the sea bed with an average 14C age 600-9(10 years older than the pre-bomb 14C age of DIC in seawater, and has a mean life in the sediments with respect to biological remineralization of at least 1000 years. Labile carbon supplied to the slope, on the other hand, is rapidly and (virtually) completely remineralized, with a mean life of <-1 year. Carbon-14 ages of fine-grained carbonate and organic carbon present within the interstices of shelf sands are consistent with this material acting as a source for the old carbon supplied to the slope. Winnowing and export of reworked carbon may contribute to the often-described relationship between organic carbon preservation and accumulation rate of marine sediments.

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“…Once extracted, the nucleic acids were combusted to CO 2 , converted to graphite targets (Vogel et al 1987), and analyzed for 14 C activities at the Center for Accelerator Mass spectrometry (CAMS) at Lawrence Livermore National Laboratory. A small portion (ϳ10%) of each CO 2 sample was analyzed for its ␦ 13 C composition (with Ϯ0.01‰ analytical precision) on a Finnigan MAT Delta S Isotope mass spectrometer at Florida State University.…”

mentioning

confidence: 99%

Radiocarbon in marine bacteria: Evidence for the ages of assimilated carbon

Cherrier

Bauer

Druffel

et al. 1999

Limnology & Oceanography

107

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It is generally accepted that marine bacteria utilize labile, recently produced components of bulk dissolved organic matter. This interpretation is based largely on indirect measurements using model compounds and plankton‐derived organic matter. Here, we present an assessment of the relative proportions of modern and older dissolved organic carbon (DOC) utilized by marine bacteria. Bacterial nucleic acids were collected from both estuarine (Santa Rosa Sound, FL) and open‐ocean (eastern North Pacific) sites, and the natural radiocarbon signatures of the nucleic acid carbon in both systems were determined. Bacterial nucleic acids from Santa Rosa Sound were significantly enriched in radiocarbon with respect to the bulk DOC and were similar to the radiocarbon signature of atmospheric CO2 at the time of sampling, indicating that these bacteria exclusively assimilate a modern component of the estuarine bulk DOC. In contrast, bacterial nucleic acids from the oceanic site were enriched in 14C relative to the bulk DOC but depleted in 14C with respect to modern surface dissolved inorganic carbon (DIC) and suspended particulate organic carbon (POCsusp). This suggests that open‐ocean bacteria assimilate both modern and older components of DOC. The distinct radiocarbon signatures of the nucleic acids at these two sites (i.e., +120 ± 17‰ estuarine vs. −34 ± 24‰ oceanic) demonstrate that natural 14C abundance measurements of bacterial biomarkers are a powerful tool for investigations of carbon cycling through microbial communities in different aquatic systems.

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¹⁴C Background Levels in An Accelerator Mass Spectrometry System

Cited by 280 publications

References 8 publications

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

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

Carbon budget for the mid-slope depocenter of the Middle Atlantic Bight

Radiocarbon in marine bacteria: Evidence for the ages of assimilated carbon

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14C Background Levels in An Accelerator Mass Spectrometry System

Cited by 280 publications

References 8 publications

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

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

Carbon budget for the mid-slope depocenter of the Middle Atlantic Bight

Radiocarbon in marine bacteria: Evidence for the ages of assimilated carbon

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¹⁴C Background Levels in An Accelerator Mass Spectrometry System