ORCID Profile
0000-0001-6141-4651
Current Organisation
University of South Florida
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Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019JG005349
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2021JG006245
Publisher: American Chemical Society (ACS)
Date: 04-12-2014
DOI: 10.1021/AC502874J
Abstract: R ed pyrolysis (RP) targets distinct components of soil and sedimentary organic carbon based on their thermochemical stabilities and allows the determination of the full spectrum of radiocarbon ((14)C) ages present in a soil or sediment s le. Extending the method into realms where more precise ages are needed or where smaller s les need to be measured involves better understanding of the blank contamination associated with the method. Here, we use a compiled data set of RP measurements of s les of known age to evaluate the mass of the carbon blank and its associated (14)C signature, and to assess the performance of the RP system. We estimate blank contamination during RP using two methods, the modern-dead and the isotope dilution method. Our results indicate that during one complete RP run s les are contaminated by 8.8 ± 4.4 μg (time-dependent) of modern carbon (MC, fM ∼ 1) and 4.1 ± 5.5 μg (time-independent) of dead carbon (DC, fM ∼ 0). We find that the modern-dead method provides more accurate estimates of uncertainties in blank contamination therefore, the isotope dilution method should be used with caution when the variability of the blank is high. Additionally, we show that RP can routinely produce accurate (14)C dates with precisions ∼100 (14)C years for materials deposited in the last 10,000 years and ∼300 (14)C years for carbon with (14)C ages of up to 20,000 years.
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2018GC008127
Abstract: The clumped isotopic composition of carbonate‐derived CO 2 (denoted Δ 47 ) is a function of carbonate formation temperature and in natural s les can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: R 13 VPDB , R 17 VSMOW , R 18 VSMOW , and λ ) impact calculated Δ 47 values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T‐Δ 47 relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, s le types, reaction temperatures, and s le preparation and analysis methods. Exploiting this large composite data set ( n = 1,253 s le replicates), we investigate the possibility for a “universal” clumped isotope calibration. We find that applying updated parameters improves the T‐Δ 47 relationship (reduces residuals) within most labs and improves overall agreement but does not eliminate all interlaboratory differences. We reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures, method of pressure baseline correction, and mass spectrometer type do not affect interlaboratory agreement. We also present new estimates of the temperature dependence of the acid digestion fractionation for Δ 47 (Δ* 25‐X ), based on combining reprocessed data from four studies, and new theoretical equilibrium values to be used in calculation of the empirical transfer function. Overall, we have ruled out a number of possible causes of interlaboratory disagreement in the T‐Δ 47 relationship, but many more remain to be investigated.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 16-11-2022
Abstract: The global carbon cycle is strongly modulated by organic carbon (OC) sequestration and decomposition. Whereas OC sequestration is relatively well constrained, there are few quantitative estimates of its susceptibility to decomposition. Fjords are hot spots of sedimentation and OC sequestration in marine sediments. Here, we adopt fjords as model systems to investigate the reactivity of sedimentary OC by assessing the distribution of the activation energy required to break OC bonds. Our results reveal that OC in fjord sediments is more thermally labile than that in global sediments, which is governed by its unique provenance and organo-mineral interactions. We estimate that 61 ± 16% of the sedimentary OC in fjords is degradable. Once this OC is remobilized and remineralized during glacial maxima, the resulting metabolic CO 2 could counterbalance up to 50 ppm of the atmospheric CO 2 decrease during glacial times, making fjords critical actors in d ening glacial-interglacial climate fluctuations through negative carbon cycling loops.
Location: United States of America
No related grants have been discovered for Brad Rosenheim.