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We employed two compelling and distinct methods, Fourier Transform Infrared Spectroscopy (FTIR) and Ramped Pyrolysis Oxidation (Ramped PyrOx), to examine the quality of organic matter (OM) stored in four peatlands located along a latitudinal gradient (Tropical (4˚N), Subtropical (27˚N), Boreal (48˚N), and Polar (68˚N)). FTIR was used to quantify the relative abundance of carbohydrates, a relatively labile compound class, and aromatics, which are more recalcitrant, in a sample set of four peat cores. These samples were then prepared using Ramped PyrOx, a second, independent method of determining OM quality that mimics the natural diagenetic maturation of OM that would take place over long timescales. Previous large-scale studies using FTIR to evaluate OM quality have observed that it generally increases with increasing latitude (more carbohydrates, less aromatics). Here, we demonstrate that the Ramped PyrOx approach both validates and complements the FTIR approach. The data stemming from each Ramped PyrOx preparation was input to a model that generates an estimated probability density function of the activation energy (E) required to break the C bonds in the sample. We separated these functions into three fractions (“lowE,” “mediumE,” and “highE”) to create Ramped PyrOx variables that could be quantitatively compared to the compound class abundance data from FTIR. In assessing the agreement between the two methods, we found three significant relationships between Ramped PyrOx and FTIR variables. LowEfractions and carbohydrate content were positively correlated (R²= 0.51) while lowEfractions were negatively correlated with aromatic content (R²= 0.58). MediumEfractions were found to be positively correlated with aromatics (R²= 0.69). 

These data correspond to the article “Deep Nitrogen Fluxes and Sources Constrained by Arc Lava Phenocrysts” by Hudak et al. submitted to Geophysical Research Letters. Table S1 includes N-He-Ar data for FIs in phenocrysts from mafic are lavas and tephras. Table S2 contains the corrected N2/3He data used for volcanic arc N flux calculations and the arc-averaged mean N arc flux. Table S3 summarizes previous literature estimates of N fluxes and the data used for those calculations. Table S4 provides the N concentrations, He concentrations, N isotope compositions of the mantle, sediments, and altered oceanic crust, as well as sediment thicknesses. Finally, Table S5 gives information about the sources of the mineral separates used for these analyses. 

Mocho-Choshuenco volcano (39.9°S, 72.0°W) produced ∼75 explosive eruptions following retreat of the >1.5-km-thick Patagonian Ice Sheet associated with the local Last Glacial Maximum (LGM, from 35 to 18 ka). Here, we extend this record of volcanic evolution to include pre- and syn-LGM lavas that erupted during the Pleistocene. We establish a long-term chronology of magmatic and volcanic evolution and evaluate the relationship between volcanism and loading/unloading of the Patagonian Ice Sheet via twenty-four 40Ar/39Ar and two 3He age determinations integrated with stratigraphy and whole-rock compositions of lava flows and glass compositions of tephra. Our findings reveal that the edifice is much younger than previously thought and preserves 106 km3 of eruptive products, of which 50% were emplaced immediately following the end of the penultimate glaciation and 20% after the end of the LGM. A period of volcanic inactivity between 37 and 26 ka, when glaciers expanded, was followed by the eruption of incompatible element-rich basaltic andesites. Several of these syn-LGM lavas dated between 26 and 16 ka, which crop out at 1500−1700 m above sea level, show ice contact features that are consistent with emplacement against a 1400- to 1600-m-thick Patagonian Ice Sheet. Small volume dacitic eruptions and two explosive rhyolitic eruptions dominate the volcanic output from 18 to 8 ka, when the Patagonian Ice Sheet began to retreat rapidly. We hypothesize that increased lithostatic loading as the Patagonian Ice Sheet grew prohibited dike propagation, thus stalling the ascent of magma, promoting growth of at least three discrete magma reservoirs, and enhancing minor crustal assimilation to generate incompatible element-rich basaltic andesitic to dacitic magmas that erupted between 26 and 17 ka. From an adjacent reservoir, incompatible element-poor dacites erupted from 17 to 12 ka. These lava flows were followed by the caldera-forming eruption at 11.5 ka of 5.3 km3 of rhyolite from a deeper reservoir atop which a silicic melt lens had formed and expanded. Subsequent eruptions of oxidized dacitic magmas from the Choshuenco cone from 11.5 to 8 ka were followed by andesitic to dacitic eruptions at the more southerly Mocho cone, as well as small flank vent eruptions of basaltic andesite at 2.5 and 0.5 ka. This complex history reflects a multi-reservoir plumbing system beneath Mocho-Choshuenco, which is characterized by depths of magma storage, oxidation states, and trace element compositions that vary over short periods of time (<2 k.y.). 

ABSTRACT Sequential thermal analysis allows for deconvoluting the refractory nature and complexity of carbon mixtures embedded in mineral matrices for subsequent offline stable carbon and radiocarbon (¹⁴C) isotope analyses. Originally developed to separate Holocene from more ancient sedimentary organic matter to improve dating of marine sediments, the Ramped Pyrolysis and Oxidation (RPO) apparatus, or informally, the “dirt burner” is now used to address pressing questions in the broad field of biogeochemistry. The growing interest in the community now necessitates improved handling and procedures for routine analyses of difficult sample types. Here we report on advances in CO₂purification during sample processing, modifications to the instrumentation at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility, and introduce sodium bicarbonate procedural standards with differing natural abundance¹⁴C signatures for blank assessment. Measurements from different environmental samples are used to compare the procedure to the different generations of sequential thermal analyses. With this study, we aim to improve the standardization of the procedures and prepare this instrumentation for innovations in online stable carbon isotopes and direct AMS-interface measurements in the future. 

ABSTRACT This note describes improvements of UV oxidation method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). The procedural blank is reduced to 2.6 ± 0.6 μg C, with Fm of 0.42 ± 0.10 and δ 13 C of –28.43 ± 1.19‰. The throughput is improved from one sample per day to two samples per day. 

ABSTRACT Radiocarbon ( 14 C) is an isotopic tracer used to address a wide range of scientific research questions. However, contamination by elevated levels of 14 C is deleterious to natural-level laboratory workspaces and accelerator mass spectrometer facilities designed to precisely measure small amounts of 14 C. The risk of contaminating materials and facilities intended for natural-level 14 C with elevated-level 14 C-labeled materials has dictated near complete separation of research groups practicing profoundly different measurements. Such separation can hinder transdisciplinary research initiatives, especially in remote and isolated field locations where both natural-level and elevated-level radiocarbon applications may be useful. This paper outlines the successful collaboration between researchers making natural-level 14 C measurements and researchers using 14 C-labeled materials during a subglacial drilling project in West Antarctica (SALSA 2018–2019). Our strict operating protocol allowed us to successfully carry out 14 C labeling experiments within close quarters at our remote field camp without contaminating samples of sediment and water intended for natural level 14 C measurements. Here we present our collaborative protocol for maintaining natural level 14 C cleanliness as a framework for future transdisciplinary radiocarbon collaborations. 

ABSTRACT This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ 13 C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ 13 C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ 13 C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.