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141 results for “isotopic composition”
Lipid extraction alters amino acid composition and bulk, but not amino acid, carbon and nitrogen isotope values
<p>Rationale: Concerns exist over observed shifts in value and variance of nitrogen isotopes following physicochemical extraction of lipids from organic matter. The mechanisms behind these apparent changes in bulk tissue δ15N values are not fully understood yet have major implications for analytical costs and integrity of data interpretations.</p> <p>Methods: Changes in proximate analysis, amino acid composition, C:N ratios, bulk tissue and amino acid δ13C and δ15N values, and resulting isotope‐based food web metrics were compared between lipid‐intact and lipid‐extracted muscle tissue of fishes spanning <1% to >20% muscle fat content to identify mechanisms of nitrogen isotope fractionation associated with physicochemical lipid extraction.</p> <p>Results: Bulk δ13C and δ15N values increased and %N, C:N ratios and crude protein content decreased following lipid extraction. Resulting bulk isotope niche spacing and overlap varied significantly between lipid‐intact and lipid‐extracted tissues. While amino acid composition significantly changed during lipid extraction, particularly for lipid‐associated amino acids (e.g., Glu, Lys, Ser), individual amino acid δ13C and δ15N values, and their associated compound‐specific isotope analysis of amino acids (CSIA‐AA)‐based food web metrics, did not.</p> <p>Conclusions: Physicochemical lipid extraction caused significant tissue composition changes (e.g., leaching of amino acids and 15N‐deplete nitrogenous waste) that affected δ13C and δ15N values and tissue %C and %N beyond simply removing lipids. However, lipid extraction did not alter individual amino acid δ13C or δ15N values or their associated CSIA‐AA‐based food web metrics.</p>
Stable isotope records and bulk chemical compositions of the early Paleogene intervals of ODP Hole 762C
<p>In this study, we examined marine carbonate sediments of the late Paleocene to middle Eocene interval from the ODP Hole 762C, located on the Exmouth Plateau in the mid-latitude eastern Indian Ocean. This new dataset includes bulk carbonate δ<sup>13</sup>C and δ<sup>18</sup>O records, as well as bulk chemical composition of the sediments. By combining δ<sup>13</sup>C data with previously published magneto-biostratigraphic records, we revised the age model based on the newly identified hyperthermal event layers.</p> <p>Description of files:</p> <ul> <li>Supporting Table S3 : Bulk δ<sup>13</sup>C and δ<sup>18</sup>O data of ODP Hole 762C.</li> <li>Supporting Table S4 : Major and trace element data of ODP Hole 762C</li> </ul>
Data reported in: Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2
<p>Tropospheric <sup>18</sup>O<sup>18</sup>O is an emerging proxy for past tropospheric ozone and free-tropospheric temperatures. The basis of these applications is the idea that isotope-exchange reactions in the atmosphere drive <sup>18</sup>O<sup>18</sup>O abundances toward isotopic equilibrium. However, previous work used an offline box-model framework to explain the <sup>18</sup>O<sup>18</sup>O budget, approximating the interplay of atmospheric chemistry and transport. This approach, while convenient, has poorly characterized uncertainties. To investigate these uncertainties, and to broaden the applicability of the <sup>18</sup>O<sup>18</sup>O proxy, we developed a scheme to simulate atmospheric <sup>18</sup>O<sup>18</sup>O abundances (quantified as ∆<sub>36</sub> values) online within the GEOS-Chem chemical transport model. These results are compared to both new and previously published atmospheric observations from the surface to 33 km. Simulations using a simplified O<sub>2</sub> isotopic equilibration scheme within GEOS-Chem show quantitative agreement with measurements only in the middle stratosphere; modeled ∆<sub>36</sub> values are too high elsewhere. Investigations using a comprehensive model of the O-O<sub>2</sub>-O<sub>3</sub> isotopic photochemical system and proof-of-principle experiments suggest that the simple equilibration scheme omits an important pressure dependence to ∆<sub>36</sub> values: the anomalously efficient titration of <sup>18</sup>O<sup>18</sup>O to form ozone. Incorporating these effects into the online ∆<sub>36</sub> calculation scheme in GEOS-Chem yields quantitative agreement for all available observations. While this previously unidentified bias affects the atmospheric budget of <sup>18</sup>O<sup>18</sup>O in O<sub>2</sub>, the modeled change in the mean tropospheric ∆<sub>36</sub> value since 1850 C.E. is only slightly altered; it is still quantitatively consistent with the ice-core ∆<sub>36</sub> record, implying that the tropospheric ozone burden increased less than ~40% over the twentieth century.</p>
Data from: Mixed Signals from the Stable Isotope Composition of Precipitation and Plant Waxes in the Northern Tropical Andes
<p>These files are the supplementary information for Pérez‐Angel, L. C., Sepúlveda, J., Montes, C., Smith, J. J., Molnar, P., González-Arango, C., Snell, K., Dildar, N., Mixed Signals from the Stable Isotope Composition of Precipitation and Plant Waxes in the Northern Tropical Andes. Journal of Geophysical Research: Biogeosciences (In Revision). </p> <p> </p> <p>This work was funded by the National Science Foundation NSF | GEO | Division of Earth Sciences (EAR): 1929199</p>
Molecular and 13C isotopic composition of diacids and related compounds in wintertime PM2.5 at three sites over Northeast Asia – Data set
<p>To investigate the spatial changes in atmospheric organic aerosols (OA) loading and composition over the northeast Asian region, fine aerosols (PM<sub>2.5</sub>) were collected at three sites: Tianjin (TJ), North China and in Padori (PD) and Daejeon (DJ), South Korea, during winter 2019. We studied the molecular distributions and compound-specific carbon isotopic composition (δ<sup>13</sup>C) of dicarboxylic acids (diacids), oxocarboxylic acids (oxoacids) and α-dicarbonyls as well as the carbonaceous and inorganic ionic components in two sets of selected samples, representing a clean and a polluted period, during the campaign. Based on the molecular distributions and δ<sup>13</sup>C of diacids and related compounds and mass ratios and linear relations of selected species, we discuss the origins of OA and the influence of long-range transported air masses on their loading and composition over Northeast Asia.</p>
Contents and isotope carbon compositions (δ13C) of main biochemical fractions in organs at different growth stages in Phyllostachys edulis
<p><em><span>Phyllostachys edulis</span></em><span> is a spectacularly fast-growing species that completes its height growth within </span><span>two</span><span> months after the shoot emerges </span><span>without producing leaves</span><span> (fast-growing period, FGP). This phase was considered heterotrophic, the carbon necessary for the growth being transferred from the mature culms via the rhizomes, although previous studies observed key enzymes and anatomical features related to C<sub>4</sub>-carbon fixation in developing culms. </span><span>We tested whether C<sub>4</sub>-photosynthesis or dark-CO2 fixation through anaplerotic reactions significantly contributes to the FGP, resulting in differences in the natural abundance of </span><span>δ<sup>13</sup>C</span><span> in bulk organic matter and organic compounds. Further, pulse-<sup>13</sup>CO<sub>2</sub>-labelling was performed on developing culms, either from the surface or from the internal hollow, to ascertain whether significant CO<sub>2</sub> fixation occurs in developing culms.</span><span> δ<sup>13</sup>C of</span><span> young </span><span>shoots and developing culms were higher (-26.3–-26.9‰) </span><span>compared to all organs of mature bamboos (-28.4</span><span>–</span><span>-30.1</span><span>‰). </span>Developing culms contained chlorophylls, most observed in the skin tissues. After <span>pulse-<sup>13</sup>CO<sub>2</sub>-labelling, t</span>he polar fraction extracted from the skin tissues was slightly enriched in <sup><span>13</span></sup><span>C, </span>and only a weak <sup><span>13</span></sup><span>C </span>enrichment was observed in inner tissues<span>. Main carbon source sustaining the FGP was not assimilated by the developing culm, while a </span><span>limited anaplerotic fixation of respired CO<sub>2</sub></span><span> cannot be excluded and is </span>more likely than <span>C<sub>4</sub>-</span>photosynthetic carbon fixation<span>.</span></p>
Mercury abundance and isotopic composition in granitic rocks: Implications for Hg cycling in the upper continental crust
<p>Mercury (Hg) is a highly volatile metal exhibiting both isotope mass-dependent (MDF, defined as δ<sup>202</sup>Hg) and mass-independent (MIF, expressed as Δ<sup>199</sup>Hg) fractionation. Assessing the Hg isotopic composition of the upper continental crust is crucial for the use of this new geochemical tool for petrogenetic tracing, particularly for understanding crust-mantle interaction. Here, we report Hg isotopic compositions of granitic rocks with distinct source affinity (I-, A-, and S-type) and of metasedimentary enclaves from the South China Craton. The results of more than 100 rock samples show large δ<sup>202</sup>Hg variations of -2.03 to 0.47 ‰ and relatively small Δ<sup>199</sup>Hg variations of -0.16 to 0.09 ‰. The S-type granites studied here exhibit higher δ<sup>202</sup>Hg values (-0.58 to 0.00 ‰; n=57) than their sedimentary protoliths (metasedimentary enclaves; -2.03 to -0.91 ‰; n=7), suggesting significant Hg-MDF during magmatic processes. The Δ<sup>199</sup>Hg values of S-type granites (-0.08 to 0.09 ‰) are indistinguishable from their sedimentary protoliths (-0.16 to 0.02 ‰), suggestive of the absence of Hg-MIF during crustal anatexis and subsequent magmatic differentiation. The I- and A-type granites studied have smaller Δ<sup>199</sup>Hg variations of -0.11 to 0.04 ‰ (n=28) and -0.07 to 0.04 ‰ (n=15), respectively, but are within the range of the S-type granites. The compositional range of all granite variants may be explained by the variable intensity of large-scale MASH (melting-assimilation-storage-homogenization) processes. Our new data combined with previously published data of igneous, sedimentary and metamorphic rocks allow us to estimate that the upper continental crust (UCC) has a Hg abundance of 13.5 ppb and a weighted average δ<sup>202</sup>Hg of -1.15 ± 1.01 ‰ (2SD), which are higher than the corresponding value of the primitive mantle, indicating the enrichment of Hg and δ<sup>202</sup>Hg in the UCC. However, the weighted average Δ<sup>199</sup>Hg value of the UCC (0.03 ± 0.15 ‰; 2SD) is undistinguished from the primitive mantle, suggesting no obvious Hg-MIF during the formation and differentiation of the continental crust.</p>
Supplementary Data to: "Organic Phases in Bivalve (Arctica islandica) Shells: Their Bulk and Amino Acid Nitrogen Stable Isotope Compositions" in Geochemistry, Geophysics, Geosystems
<p>This dataset contains the data generated for publication "Organic Phases in Bivalve (<em>Arctica islandica</em>) Shells: Their Bulk and Amino Acid Nitrogen Stable Isotope Compositions", including the following files:</p> <p>Specimen_ID_shell_morphology_measurement: Description of locality of collection, shell ID, shell working ID and the shell morphology measurement which can be referred to Section 2.1 of the manuscript.</p> <p>EA_IRMS_raw_error_propagate: This file contains data showing the m/z 28 signal intensities of all measurements and the error propagation that mentioned in Section 2.3 of the manuscript. It also includes the calculation of analytical accuracy and precision. </p> <p>Statistics: The file contains the summary of statistical analyses performed in this manuscript. Refer to Section 2.7 and 3.3.</p> <p>Recovery: It contains the recovery of the total nitrogen contents or amino acid concentrations after different treatments and this was mentioned in Section 4.1 of the manucript.</p> <p>Mass_balance: The computation procedure that showed in Section 3.4 and discussed in Section 4.3 can be traced in this file.</p> <p>GC-C-IRMS_long_term_sd: The file shows the long-term precision of GC-C-IRMS computed from the mixed standard of amino acids </p> <p>BSIA_d15N: The file contains all the bulk d15N data that used in this manuscript.</p> <p>CSIA_d15N: The file contains all the amino acid d15N data that used in this manuscript.</p> <p>AA_Composition: The file shows AA percent data that used in this manuscript.</p> <p><br> For details see main text of the manuscript.</p> <p><br> </p>
Data from: Isotopic composition of particulate black carbon in the northern Indian Ocean
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Lipid extraction alters amino acid composition and bulk, but not amino acid, carbon and nitrogen isotope values
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Biochemical and biophysical drivers of the hydrogen isotopic composition of carbohydrates and acetogenic lipids
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Contents and isotope carbon compositions (δ13C) of main biochemical fractions in organs at different growth stages in Phyllostachys edulis
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Data reported in: Effects of ozone isotopologue formation on the clumped-isotope composition of atmospheric O2
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Data from: Oxygen isotope composition of teeth suggests endothermy and possible migration in some Late Cretaceous shark taxa from the Gulf Coastal Plain, USA
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Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of Island Scrub-Jays (Aphelocoma insularis) in pine and oak habitats
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The oxygen isotope compositions of large numbers of small cosmic spherules: Implications for their sources and the isotopic composition of the upper atmosphere
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Chemistry and isotopic composition of resource pools in lakes of the Sierra Nevada, CA
The extent to which terrestrial organic matter supports aquatic consumers remains uncertain because factors regulating resource flows are poorly understood. We sampled 12 lakes throughout the Sierra Nevada (California, USA) spanning large gradients in elevation and size to evaluate how watershed attributes and lake morphometry influence resource flows to lake carbon pools and zooplankton. We found that the size and composition of carbon pools in lakes were often more strongly determined by watershed or lake features rather than by elevational position. Using three different tracers of resource origin (δ13C, Δ14C, C:N ratio), we found terrestrial contributions to most lake resource pools (DOC, POM, sediments) and pelagic consumers (zooplankton) were more strongly related to local-scale watershed features such as vegetation cover or watershed area:lake area rather than to elevation. Landscape patterns in multiple tracers indicated consistent contribution of within-lake C sources to bulk resource pools across elevations (POM, sediments, zooplankton). δ13C-enrichment of lake C pools and overlap with δ13C of terrestrial resources can arise due to reduced fractionation of 13C by phytoplankton under CO2 limitation, therefore we recommend careful consideration of potential environmental drivers when interpreting among-lake patterns in δ13C. Our findings emphasize the importance of local-scale variation in mediating terrestrial contributions to lake food webs.
Stable Isotopic Composition of Nitrates and POM in BES Streams
In the Baltimore urban long-term ecological research (LTER) project, (Baltimore Ecosystem Study, BES) we use the watershed approach to evaluate integrated ecosystem function. The LTER research is centered on the Gwynns Falls watershed, a 17,150 ha catchment that traverses a gradient from the urban core of Baltimore, through older urban residential (1900 - 1950) and suburban (1950- 1980) zones, rapidly suburbanizing areas and a rural/suburban fringe. Stable isotopic analyses were carried out on stream samples collected bi-weekly from June 2005 through December 2005 as part of the routine Baltimore LTER sampling. Sites included POBR (forest), MCDN (agricultural), BARN (low-residential), GFGL (suburban), DRKR (urban), GFCP (urban), and RGHT (storm drain). Samples were also taken from a small tributary to the Gwynns Falls (GFGR), approximately 300 m above GFCP, that was highly contaminated with sewage. A major sewer leak to this stream was identified and repaired in April 2004. Stable isotopic analyses of soil water underneath fertilized lawns and atmospheric deposition was measured in long-term lawn study plots on the campus of the University of Maryland Baltimore County. Storm samples were also collected from 6 locations (DR1, DR3.1, DR3.2, DR4, DR5, DRKR gauge) within the Dead Run watershed over July 2005. At one site (DR3), two sets of samples were collected, one just above (DR3.1) and just below (DR3.2) an overflowing sewer. All stormflow samples were collected on the receding limb of the storm hydrograph, as the flashy nature of these urban streams makes sampling the rising limb difficult in terms of both timing and personal safety. Nitrate concentrations are a separate set of chemical analyses than the routine weekly analyses.
Stable isotope composition (d18O) of seawater from stations in the Palmer LTER Study Site
The west Antarctic Peninsula (WAP) is a region of marked climatic variability, exhibiting strong changes in sea ice extent, retreat of the majority of its glaciers, and shifts in the amount and form of precipitation. These changes can have significant impacts on the oceanic freshwater budget and marine biogeochemical processes; it is thus important to ascertain the relative balance of the drivers, and the spatial scales over which they operate. We present a new 7-year summer-season (October to March; 2011 to 2018) series of oxygen isotopes in seawater (δ18O), augmented with some winter sampling, collected adjacent to Anvers Island at the WAP. These data are used to attribute oceanic freshwater changes to sea ice and meteoric sources, and to deduce information on the spatial scales over which the changes are driven. Sea ice melt shows strong seasonality (~9% range) and marked interannual changes, with pronounced maxima in seasons 2013/14 and 2016/17. Both of these extrema are driven by anomalous winds, but reflect strongly contrasting dynamic and thermodynamic sea ice responses. Meteoric water also shows marked seasonality (~7% range), with interannual variability reflecting changes in the input of accumulated precipitation and glacial melt to the ocean. Unlike sea ice melt, meteoric water extremes are especially pronounced in thin (<10m) surface layers close to Marr Ice Piedmont, associated with enhanced ocean stratification. Isotopic tracers help to deconvolve the complex spatio-temporal scales inherent in the coastal freshwater budget, and hence improve knowledge of the separate and cumulative physical and ecological impacts.
Dataset: Seasonality, drivers, and isotopic composition of soil CO2 fluxes from tropical forests of the Congo Basin
<p>These data sets contain data from soil CO2 flux measurements and its drivers (soil moisture, soil temperature) from lowland and montane tropical forests of the Congo Basin. Additionally, 13C values of soil emitted CO2, SOC, Leaflitter, and stream dissolved CO2 are reported. A Manuscript using these data sets has been submitted to Biogeosciences</p>
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