TY - JOUR T1 - Using Stable Carbon Isotopes to Quantify Radiocarbon Reservoir Age Offsets in the Coastal Black SeaAbstract JF - Radiocarbon Y1 - 2019 A1 - Soulet, Guillaume A1 - Giosan, Liviu A1 - Flaux, Clément A1 - Galy, Valier KW - Black Sea KW - Carbon cycle KW - freshwater reservoir effect KW - Geochronology KW - Reservoir age AB - Constraining radiocarbon (C-14) reservoir age offsets is critical to deriving accurate calendar-age chronologies from C-14 dating of materials which did not draw carbon directly from the atmosphere. The application of C-14 dating to such materials is severely limited in hydrologically sensitive environments like the Black Sea because of the difficulty to quantify reservoir age offsets, which can vary quickly and significantly through time, due to the dynamics of the biogeochemical cycling of carbon. Here we reconstruct C-14 reservoir age offsets (Rshell-atm) of Holocene bivalve shells from the coastal Black Sea relatively to their contemporaneous atmosphere. We show that the C-14 reservoir age offset and the stable carbon isotope composition of bivalve shells are linearly correlated in this region. From a biogeochemical standpoint, this suggests that inorganic stable carbon isotope and C-14 compositions of Black Sea coastal waters are controlled by the balance between autochthonous primary productivity and heterotrophic respiration of allochthonous pre-aged terrestrial organic matter supplied by rivers. This provided an important implication for Black Sea geochronology as the reservoir age offset of C-14-dated bivalve shell can be inferred from its stable carbon isotope composition. Our results provide a fundamental and inexpensive geochemical tool which will considerably improve the accuracy of Holocene calendar age chronologies in the Black Sea. VL - 61 UR - https://www.cambridge.org/core/product/identifier/S0033822218000619/type/journal_articlehttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822218000619 IS - 1 ER - TY - JOUR T1 - Assessing the Blank Carbon Contribution, Isotope Mass Balance, and Kinetic Isotope Fractionation of the Ramped Pyrolysis/Oxidation Instrument at NOSAMS JF - Radiocarbon Y1 - 2017 A1 - Hemingway, Jordon D A1 - Galy, Valier V A1 - Gagnon, Alan R A1 - Grant, Katherine E A1 - Rosengard, Sarah Z A1 - Soulet, Guillaume A1 - Zigah, Prosper K A1 - McNichol, Ann P KW - Ramped PyrOx; blank assessment; kinetic fractionation AB - We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150-1000 degrees C; 5 degrees C x min(-1)) to be (3.7 +/- 0.6) mu g C with an Fm value of 0.555 +/- 0.042 and a delta C-13 value of (-29.0 +/- 0.1)parts per thousand VPDB. Additionally, we provide equations for RPO Fm and delta C-13 blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk delta C-13 values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent delta C-13 depletion within the RPO instrument (mean-bulk: mu = -0.8 parts per thousand; +/- 1 sigma = 0.9 parts per thousand; n = 66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean-bulk: mu = 0.005; +/- 1 sigma = 0.014; n = 36). Lastly, we show there exists no significant intra-sample delta C-13 variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between C-13- and C-12-containing compounds ((13-12)Delta E) of 0.3-1.8 J x mol(-1), indicating that blank and mass-balance corrected RPO delta C-13 values accurately retain carbon source isotope signals to within 1-2 parts per thousand. VL - 59223–22493970409 UR - https://www.cambridge.org/core/product/identifier/S0033822217000030/type/journal_article IS - 01 JO - Radiocarbon ER - TY - JOUR T1 - A Note on Reporting of Reservoir C-14 Disequilibria and Age Offsets JF - RADIOCARBON Y1 - 2016 A1 - Soulet, Guillaume A1 - Skinner, Luke C. A1 - Beaupré, Steven R. A1 - Galy, Valier KW - freshwater effect KW - hardwater effect KW - radiocarbon KW - Reservoir age KW - Reservoir effect KW - ventilation age AB - Reservoir age offsets are widely used to correct marine and speleothem radiocarbon age measurements for various calibration purposes. They also serve as a powerful tracer for carbon cycle dynamics. However, a clear terminology regarding reservoir age offsets is lacking, sometimes leading to miscalculations. This note seeks to provide consistent conventions for reporting reservoir C-14 disequilibria useful to a broad range of environmental sciences. This contribution introduces the (FR)-R-14 and R-14 metrics to express the relative C-14 disequilibrium between two contemporaneous reservoirs and the R metric as the associated reservoir age offset. VL - 58 ER - TY - JOUR T1 - Methods and codes for reservoir-atmosphere C-14 age offset calculations JF - QUATERNARY GEOCHRONOLOGY Y1 - 2015 A1 - Soulet, Guillaume KW - Calibration curve KW - Dead carbon fraction KW - Radiocarbon modeling KW - Reservoir age KW - Reservoir effect KW - Uncalibration process AB - Reservoir C-14 age offsets are invaluable tracers for past changes in carbon cycle and oceanic circulation. Reconstruction of reservoir age offsets with time is also required for calibration purposes (reconstruction of atmospheric calibration curve, calibration of non-atmospheric radiocarbon ages). Thus, properly propagating the various uncertainties linked to reservoir age offset is important for proper interpretation. However, approaches for reservoir age offset calculation especially when considering pairs of reservoir-derived C-14 and calenidar ages are usually not detailed and inadequate for proper propagation of uncertainties. Here, the various ways to properly calculate reservoir age offsets are described with a focus on a new approach when considering pairs of C-14 and calendar ages. This approach maps the calendar age distribution onto the C-14 time scale prior to reservoir age offset calculation the ``uncalibration-convolution process{''}. R codes computing reservoir age offsets based on available data are presented. Finally, a case study focusing on the reconstruction of the speleothem-atmosphere C-14 age offsets of speleothem C-14 data used in the latest release of the atmospheric calibration curve is discussed. (C) 2015 Elsevier B.V. All rights reserved. VL - 29 ER - TY - JOUR T1 - Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate JF - QUATERNARY SCIENCE REVIEWS Y1 - 2015 A1 - Toucanne, Samuel A1 - Soulet, Guillaume A1 - Freslon, Nicolas A1 - Jacinto, Ricardo Silva A1 - Dennielou, Bernard A1 - Zaragosi, Sebastien A1 - Eynaud, Frédérique A1 - Bourillet, Jean-Francois A1 - Bayon, Germain KW - Channel River KW - Deglaciation KW - European ice-sheet KW - Meltwater KW - Neodymium KW - Termination AB - Reconstructing Northern Hemisphere ice-sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes. To date, research efforts have mainly focused on the North American (Laurentide) ice-sheets (LIS), leaving the potential role of the European Ice Sheet (EIS), and of the Scandinavian ice-sheet (SIS) in particular, largely unexplored. Using neodymium isotopes in detrital sediments deposited off the Channel River, we provide a continuous and well-dated record for the evolution of the EIS southern margin through the end of the last glacial period and during the deglaciation. Our results reveal that the evolution of EIS margins was accompanied with substantial ice recession (especially of the SIS) and simultaneous release of meltwater to the North Atlantic. These events occurred both in the course of the EIS to its LGM position (i.e., during Heinrich Stadial -HS- 3 and HS2; similar to 31-29 ka and similar to 26-23 ka, respectively) and during the deglaciation (i.e., at similar to 22 ka, similar to 20-19 ka and from 18.2 +/- 0.2 to 16.7 +/- 0.2 ka that corresponds to the first part of HS1). The deglaciation was discontinuous in character, and similar in timing to that of the southern LIS margin, with moderate ice-sheet retreat (from 22.5 +/- 0.2 ka in the Baltic lowlands) as soon as the northern summer insolation increase (from similar to 23 ka) and an acceleration of the margin retreat thereafter (from similar to 20 ka). Importantly, our results show that EIS retreat events and release of meltwater to the North Atlantic during the deglaciation coincide with AMOC destabilisation and interhemispheric climate changes. They thus suggest that the EIS, together with the LIS, could have played a critical role in the climatic reorganization that accompanied the last deglaciation. Finally, our data suggest that meltwater discharges to the North Atlantic produced by large-scale recession of continental parts of Northern Hemisphere ice sheets during HS, could have been a possible source for the oceanic perturbations (i.e., AMOC shutdown) responsible for the marine-based ice stream purge cycle, or so-called HE's, that punctuate the last glacial period. (C) 2015 Elsevier Ltd. All rights reserved. VL - 123 ER -