Air pressure and cosmogenic isotope production
TL;DR: In this article, it was shown that the cosmic ray flux increases at higher altitude as air pressure and the shielding effect of the atmosphere decrease, and that altitude-dependent scaling factors are required to compensate for this effect in calculating cosmic ray exposure ages.
Abstract: The cosmic ray flux increases at higher altitude as air pressure and the shielding effect of the atmosphere decrease. Altitude-dependent scaling factors are required to compensate for this effect in calculating cosmic ray exposure ages. Scaling factors in current use assume a uniform relationship between altitude and atmospheric pressure over the Earth's surface. This masks regional differences in mean annual pressure and spatial variation in cosmogenic isotope production rates. Outside Antarctica, air pressures over land depart from the standard atmosphere by ±4.4 hPa (1σ) near sea level, corresponding to offsets of ±3–4% in isotope production rates. Greater offsets occur in regions of persistent high and low pressure such as Siberia and Iceland, where conventional scaling factors predict production rates in error by ±10%. The largest deviations occur over Antarctica where ground level pressures are 20–40 hPa lower than the standard atmosphere at all altitudes. Isotope production rates in Antarctica are therefore 25–30% higher than values calculated by scaling Northern Hemisphere production rates with conventional scaling factors. Exposure ages of old Antarctic surfaces, especially those based on cosmogenic radionuclides at levels close to saturation, may be millions of years younger than published estimates.
Citations
More filters
TL;DR: The responses of the Northern and Southern Hemispheres differed significantly, which reveals how the evolution of specific ice sheets affected sea level and provides insight into how insolation controlled the deglaciation.
Abstract: We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.
2,691 citations
TL;DR: In this paper, the authors present the theory necessary for interpreting cosmogenic nuclide data, reviews estimates of parameters, describes strategies and practical considerations in field applications, and assesses sources of error in interpreting Cosmogenic Nuclide measurements.
1,758 citations
TL;DR: In this paper, the authors present a single complete and straightforward method that reflects currently accepted practices and is consistent with existing production rate calibration measurements, which is intended to enable geoscientists, who wish to use cosmogenic-nuclide exposure age or erosion rate measurements in their work, to calculate exposure ages and erosion rates; compare previously published exposure ages on a common basis; and evaluate the sensitivity of their results to differences between published production rate scaling schemes.
1,708 citations
Cites background or methods from "Air pressure and cosmogenic isotope..."
...Stone (2000), Dunai (2000), Farber et al. (2005), and Staiger et al. (2007) discuss this in more detail....
[...]
...For sites in Antarctica, users should choose a height–pressure relationship from Radok et al. (1996); Stone (2000) discusses the relationship between this and the standard atmosphere in detail....
[...]
...This is a different averaging procedure than is used in Stone (2000)....
[...]
...We used a set of calibration measurements that is similar to that used by Stone (2000)....
[...]
...With regard to (26)Al measurements, Nishiizumi (2004) and Wallner et al. (2000) compared Al isotope ratio standards in use at various AMS laboratories....
[...]
TL;DR: In this paper, the authors present a new time-slice reconstruction of the Eurasian ice sheets (British-Irish, Svalbard-Barents-Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 years and at four selected time periods back to 40 years.
Abstract: We present a new time-slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27–26 ka) than the eastern limit on the Russian Plain (at c. 20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm2) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continental-scale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA (www.bcdc.no; http://doi.pangaea.de/10.1594/PANGAEA.848117).
757 citations
Cites methods from "Air pressure and cosmogenic isotope..."
...(2013) and report values using ‘St’ scaling (Lal 1991; Stone 2000),...
[...]
...2 (Balco et al. 2008) using the ‘Arctic’ production rate calibration dataset of Young et al. (2013) and report values using ‘St’ scaling (Lal 1991; Stone 2000), which gives a reference production rate of 3.96 0.15 atoms g 1 a 1 for 10Be....
[...]
TL;DR: In this paper, the authors used in-situ produced cosmogenic nuclides (e.g. 10Be, 26Al), mostly in quartz from alluvial sediment.
605 citations
Cites background from "Air pressure and cosmogenic isotope..."
...The intensity of secondary cosmic rays also depends on air pressure [51]....
[...]
References
More filters
TL;DR: In this paper, the authors present theoretical estimates of the production rates of isotopes of He, Ne and Ar based on available cross-section data, and discuss the implications of these parameters for single and multiple nuclide studies in terms of the erosion models considered.
2,322 citations
01 Jan 1967
TL;DR: In this article, it was shown that matter which is exposed to cosmic radiation undergoes characteristic changes in its chemical and isotopic composition, and such irradiated material can be found in many places on earth and belongs to either of two categories:
Abstract: Matter which is exposed to cosmic radiation undergoes characteristic changes in its chemical and isotopic composition. Such irradiated material can be found in many places on earth and belongs to either of two categories:
946 citations
TL;DR: In this paper, the concentrations of Be-10 and Al-26 in quartz crystals extracted from glacially polished granitic surfaces from the Sierra Nevada range were studied and the most accurate estimates of absolute production rates of three nuclides in SiO2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43.8-44.6 N and altitudes 2.1-3.6 km.
Abstract: The concentrations of Be-10 and Al-26 in quartz crystals extracted from glacially polished granitic surfaces from the Sierra Nevada range are studied. These surfaces are identified with the glacial advance during the Tioga period about 11,000 yr ago. The measurements yield the most accurate estimates to date for the absolute production rates of three nuclides in SiO2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43.8-44.6 N and altitudes 2.1-3.6 km.
533 citations
TL;DR: In this paper, the authors presented new scaling factors for in situ produced cosmogenic nuclides, which incorporate the influence of the non-dipole contributions to the geomagnetic field on the cosmic ray flux.
361 citations
TL;DR: In this article, the production of cosmogenic nuclides in the Earth's atmospheric and in-situ in the surface is discussed and the production rates of 3 H, 7 Be, 10 Be, 14 C, 21 Ne, 26 Al, and 36 Cl agree well with experimental measurements for certain minerals in surface samples.
286 citations