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      Ultra-Microscale (5–25 μg C) Analysis of Individual Lipids by 14C AMS: Assessment and Correction for Sample Processing Blanks

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      Radiocarbon

      Cambridge University Press (CUP)

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          Abstract

          Measurements of the natural abundance of radiocarbon in biomarker molecules can be used to elucidate the biogeochemical roles of marine bacteria and archaea in the oceanic water column. However, the relatively low concentration of biomass, especially below the euphotic zone, inevitably results in small sample sizes for compound-specific analyses. In ultra-microscale Δ 14C measurements, which we define as measurements on samples smaller than 25 μg C, the process of isolating pure compounds and preparing them for measurement adds significant background carbon. This additional blank carbon can contribute up to 40% of the total sample mass; therefore, it is necessary to quantify all components of the processing blank in order to make appropriate corrections. Complete propagation of error is critical in order to report the correct analytical uncertainty. The carbon blank is composed of at least 3 different sources: i) those that scale in proportion to the mass of the sample; ii) sources that contribute a constant mass of blank, e.g. closed-tube combustion; and iii) contaminants from vacuum lines and/or other aspects of sample handling that are difficult to quantify. We approached the problem of correcting for the total sample processing blank by deriving a 4-part isotopic mass balance based on separating the 3 exogenous components from the sample. Subsequently, we derived the appropriate equations for the full propagation of error associated with these corrections. Equations for these terms are presented. Full treatment of a set of raw data is demonstrated using compound-specific Δ 14C data from the North Central Pacific water column.

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          Ubiquity and diversity of ammonia-oxidizing archaea in water columns and sediments of the ocean.

          Nitrification, the microbial oxidation of ammonia to nitrite and nitrate, occurs in a wide variety of environments and plays a central role in the global nitrogen cycle. Catalyzed by the enzyme ammonia monooxygenase, the ability to oxidize ammonia was previously thought to be restricted to a few groups within the beta- and gamma-Proteobacteria. However, recent metagenomic studies have revealed the existence of unique ammonia monooxygenase alpha-subunit (amoA) genes derived from uncultivated, nonextremophilic Crenarchaeota. Here, we report molecular evidence for the widespread presence of ammonia-oxidizing archaea (AOA) in marine water columns and sediments. Using PCR primers designed to specifically target archaeal amoA, we find AOA to be pervasive in areas of the ocean that are critical for the global nitrogen cycle, including the base of the euphotic zone, suboxic water columns, and estuarine and coastal sediments. Diverse and distinct AOA communities are associated with each of these habitats, with little overlap between water columns and sediments. Within marine sediments, most AOA sequences are unique to individual sampling locations, whereas a small number of sequences are evidently cosmopolitan in distribution. Considering the abundance of nonextremophilic archaea in the ocean, our results suggest that AOA may play a significant, but previously unrecognized, role in the global nitrogen cycle.
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            • Record: found
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            Cycling of dissolved and particulate organic matter in the open ocean

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              Radiocarbon dating of diatom-bound organic compounds

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                Author and article information

                Journal
                applab
                Radiocarbon
                Radiocarbon
                Cambridge University Press (CUP)
                0033-8222
                1945-5755
                2007
                July 18 2016
                2007
                : 49
                : 01
                : 69-82
                10.1017/S0033822200041904
                © 2007

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