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
Dr Vasilii Petrenko1, Dr. Segev BenZvi2, Dr. Andrew Smith3, Dr. Michael Dyonisius4, Dr. Benjamin Hmiel5, Dr. Peter Neff6, Dr. Christo Buizert7, Dr. Jeffrey Severinghaus8
1Department of Earth and Environmental Sciences, University Of Rochester, Rochester, United States, 2Department of Physics and Astronomy, University of Rochester, Rochester, United States, 3Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, Australia, 4Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark, 5Environmental Defense Fund, New York, United States, 6Department of Soil, Water and Climate, University of Minnesota Twin Cities, Saint Paul, United States, 7College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, United States, 8Scripps Institution of Oceanography, University of California San Diego, La Jolla, United States
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.
Vasilii Petrenko is an atmospheric scientist and paleoclimatologist who is interested in using measurements of 14C and other isotopes to study processes in the past and modern atmosphere.