Browsing by Author "BenZvi, S"

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    Characterization of in situ cosmogenic 14CO in glacial ice and applications of ice core 14CO as a tracer
    (American Geophysical Union (AGU), 2022-12-15) Petrenko, VV; Hmiel, B; Dyonisius, MN; Smith, AM; Neff, PD; BenZvi, S
    Carbon-14 (14C) is included in glacial ice via trapping of air and in situ cosmogenic production. In the carbon monoxide phase (14CO), ice core 14C has two promising applications. First, the trapped atmospheric component of 14CO has the potential to serve as a tracer of past hydroxyl radical (OH) abundance and variability. Second, the in situ cosmogenic component can in principle be used to reconstruct variations in the past flux of galactic cosmic rays. A detailed understanding of the in situ cosmogenic 14CO production and retention in ice is needed to disentangle the trapped atmospheric and in situ cosmogenic components in measurements of ice core 14CO. We will present the most recent interpretations of ice core 14CO measurements from Taylor Glacier, Antarctica and Summit, Greenland. Taylor Glacier is an ablation site with easily accessible ancient (>50 kyr) ice at the surface that allows for the determination of in situ cosmogenic 14CO production rates in the absence of a trapped atmospheric component. Summit is a traditional ice coring site that allows for the examination of how well in situ cosmogenic 14CO is retained in the firn. The results form the basis for the interpretation of new measurements from Law Dome, Antarctica, which are aimed at reconstructing paleoatmospheric 14CO. The results also support the feasibility of using 14CO measurements at a low-accumulation site such as Dome C, Antarctica to study past variations in the galactic cosmic ray flux.
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    Obtaining a history of the flux of cosmic rays using in situ cosmogenic 14C trapped in polar ice
    (International Union of Pure and Applied Physics (IUPAP), 2019-07-24) BenZvi, S; Petrenko, VV; Hmiel, B; Dyonisius, MN; Smith, AM; Yang, B; Hua, Q
    Carbon-14 (14C) is produced in the atmosphere when neutrons from cosmic-ray air showers are captured by 14N nuclei. Atmospheric 14C becomes trapped in air bubbles in polar ice as compacted snow (firn) transforms into ice. 14C is also produced in situ in ice grains by penetrating cosmic-ray neutrons and muons. Recent ice core measurements indicate that in the 14CO phase, the 14C is dominated by the in situ cosmogenic component at most ice coring sites. Thus, it should be possible to use ice-bound 14CO to reconstruct the historical flux of cosmic rays at Earth, without the transport and deposition uncertainties associated with 10Be or the carbon cycle uncertainties affecting atmospheric 14CO2. The measurements will be sensitive to the cosmic-ray flux above the energy range most affected by solar modulation. We present estimates of the expected sensitivity of 14CO in ice cores to the historical flux of Galactic cosmic rays, based on recent studies of 14CO in polar ice. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0)
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    The potential of using in situ cosmogenic 14CO in ice cores at Dome C to examine the assumption of a constant galactic cosmic ray flux
    (American Geophysical Union (AGU), 2021-12-17) Petrenko, VV; BenZvi, S; Smith, AM; Dyonisus, MN; Hmiel, B; Neft, PD; Buizert, C; Severinghaus, JP
    Cosmogenic nuclides produced in the Earth’s atmosphere and at the surface are powerful proxies for important climate processes and drivers. Records of atmospherically-produced 14C and 10Be have been used to reconstruct past solar activity and solar irradiance. 10Be, 14C, 26Al and other nuclides produced in surface rock are widely used in studies of past ice dynamics and extent. All these studies generally assume that the galactic cosmic ray (GCR) flux at Earth is constant in time. However, the available geochemical evidence for GCR flux constancy is complicated by processes that are not fully constrained. As a result, the assumption of a constant GCR flux may be uncertain by 30% or more. Cosmic rays also produce 14C in situ in glacial ice and firn; this 14C then reacts rapidly to form mainly 14CO and 14CO2. Almost all of the 14C produced in the firn layer is lost to the atmosphere via gas diffusion, and in situ 14C only starts to accumulate in the deepest firn (≈95 m at Dome C) where gas exchange with the atmosphere effectively stops. At this depth, all of the in situ 14C production is via interactions with deep-penetrating muons. Such muons are generated by high-energy primary GCRs that are unaffected by geomagnetic and solar modulation. Further, at sites with low snow accumulation such as Dome C, in situ 14CO strongly dominates over trapped atmospheric 14CO in the ice. As a result, 14CO in ice at Dome C would provide a record of the past GCR flux that is virtually free of confounding factors and should allow to constrain any past flux variations to within ≈ 10%. This presentation will provide a brief overview of results from recent studies of in situ cosmogenic 14CO in Greenland and Antarctica, as well as predictions for Dome C under a range of different GCR flux scenarios.
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    The potential of using in situ cosmogenic 14CO in ice cores at Dome C to examine the assumption of a constant galactic cosmic ray flux
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Petrenko, VV; BenZvi, S; Smith, AM; Dyonisius, MN; Hmiel, B; Neff, PD; Buizert, C; Severinghaus, JP
    Cosmogenic nuclides produced in the Earth’s atmosphere and at the surface are powerful proxies for important climate processes and drivers. Records of atmospherically-produced 14C and 10Be have been used to reconstruct past solar activity and solar irradiance. 10Be, 14C, 26Al and other nuclides produced in surface rock are widely used in studies of past ice dynamics and extent. All these studies generally assume that the galactic cosmic ray (GCR) flux at Earth is constant in time. However, the available geochemical evidence for GCR flux constancy is complicated by processes that are not fully constrained. As a result, the assumption of a constant GCR flux may be uncertain by 30% or more. Cosmic rays also produce 14C in situ in glacial ice and firn; this 14C then reacts rapidly to form mainly 14CO and 14CO2. Almost all of the 14C produced in the firn layer is lost to the atmosphere via gas diffusion, and in situ 14C only starts to accumulate in the deepest firn (≈95 m at Dome C) where gas exchange with the atmosphere effectively stops. At this depth, all of the in situ 14C production is via interactions with deep-penetrating muons. Such muons are generated by highenergy primary GCRs that are unaffected by geomagnetic and solar modulation. Further, at sites with low snow accumulation such as Dome C, in situ 14CO strongly dominates over trapped atmospheric 14CO in the ice. As a result, 14CO in ice at Dome C would provide a record of the past GCR flux that is virtually free of confounding factors and should allow to constrain any past flux variations to within ≈ 10%. This presentation will provide a brief overview of results from recent studies of in situ cosmogenic 14CO in Greenland and Antarctica, as well as predictions for Dome C under a range of different GCR flux scenarios. © The Authors