cosmogenic isotopes
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2021 ◽  
Author(s):  
John Greenlee ◽  
Silas Dean ◽  
Nicolas Waldmann

<p>This study aims to reconstruct the paleoenvironmental and climatic conditions affecting the Levantine corridor during the early Pliocene. For the purpose of this study, a ~20 m continuous core sequence was retrieved out of the ~200 m long, tilted Erk el Ahmar sequence previously dated by cosmogenic isotopes to ~3.5 Ma. The record include intercalating units consisting of sands, silts, and clays that were sampled in high resolution in order to analyze a variety of sedimentological and geochemical proxies of past climate and environmental changes. We present new preliminary, high-resolution sedimentological (laser diffraction granulometry), petrophysical (magnetic susceptibility) and compositional (X-ray fluorescence) data along with accompanying statistical analysis performed with an advanced suite of data-science tools. These results reveal new cycles of environmental change in the area, which appears to be orbitally controlled, and include dramatic changes also indicated by discrete strata of fossil fragments. Moreover, cycles of deposition can also provide hints on the major hydrological controlling mechanisms. This project provides new light into favorable conditions for the subsistence of perennial lake environments in the Levantine Corridor, which in turn may have facilitated faunal migration between Africa and Eurasia.</p>


2021 ◽  
Author(s):  
Mike Bentley ◽  
Dominic Hodgson ◽  
Andy Hein ◽  
Steve Binnie ◽  
Steve Moreton

<p>The post-LGM thinning history of the East Antarctic Ice Sheet is not yet well constrained. Here we report some integrated observations and analyses that constrain the ice sheet thinning history in Western Dronning Maud Land and Coats Land, adjacent to the easternmost Weddell Sea, which is a key area of uncertainty in ice sheet reconstructions. Geomorphological observations show a distinct series of weathering zones with fresh erratics only found in a relatively narrow zone above the present ice sheet margin. We report cosmogenic surface exposure dates of erratics in the different weathering zones, using <sup>10</sup>Be and in situ <sup>14</sup>C. We further report a large number of radiocarbon ages on sub-fossil bird vomit (regurgitated proventricular stomach oil, sometimes termed ‘mumiyo’) from nesting snow petrels (Pagodroma nivea) which record periods of ice sheet absence. Together these analyses allow us to determine a more tightly constrained thinning history of the ice sheet in this sector. We discuss the implications of this thinning history for geologically-based ice sheet reconstructions and for ice sheet models.</p>


2021 ◽  
Author(s):  
Kseniia Golubenko ◽  
Eugene Rozanov ◽  
Genady Kovaltsov ◽  
Ari-Pekka Leppänen ◽  
Ilya Usoskin

<p>We present the first results of modelling of the short-living cosmogenic isotope <sup>7</sup>Be production, deposition, and transport using the chemistry-climate model SOCOLv<sub>3.0</sub> aimed to study solar-terrestrial interactions and climate changes. We implemented an interactive deposition scheme,  based on gas tracers with and without nudging to the known meteorological fields. Production of <sup>7</sup>Be was modelled using the 3D time-dependent Cosmic Ray induced Atmospheric Cascade (CRAC) model. The simulations were compared with the real concentrations (activity) and depositions measurements of <sup>7</sup>Be in the air and water at Finnish stations. We have successfully reproduced and estimated the variability of the cosmogenic isotope <sup>7</sup>Be produced by the galactic cosmic rays (GCR) on time scales longer than about a month, for the period of 2002–2008. The agreement between the modelled and measured data is very good (within 12%) providing a solid validation for the ability of the SOCOL CCM to reliably model production, transport, and deposition of cosmogenic isotopes, which is needed for precise studies of cosmic-ray variability in the past. </p>


2020 ◽  
Vol 232 ◽  
pp. 02002
Author(s):  
Walter Kutschera ◽  
Gernot Patzelt ◽  
Joerg M. Schaefer ◽  
Christian Schlüchter ◽  
Peter Steier ◽  
...  

A brief review of the movements of Alpine glaciers throughout the Holocene in the Northern Hemisphere (European Alps) and in the Southern Hemisphere (New Zealand Southern Alps) is presented. It is mainly based on glacier studies where 14C dating, dendrochronology and surface exposure dating with cosmogenic isotopes is used to establish the chronology of advances and retreats of glaciers. An attempt is made to draw some general conclusions on the temperature and climate differences between the Northern and Southern Hemisphere.


Author(s):  
T Jull ◽  
M Baroni ◽  
A Feinberg ◽  
G Kovaltsov ◽  
F Mekhaldi ◽  
...  

2019 ◽  
Vol 625 ◽  
pp. A28 ◽  
Author(s):  
R. H. Cameron ◽  
M. Schüssler

Power spectra of solar activity based on historical records of sunspot numbers and on cosmogenic isotopes show peaks with enhanced power apart from the dominant 11-year solar cycle, such as the 90-year Gleissberg cycle or the 210-year de Vries cycle. In a previous paper we have shown that the overall shape of the power spectrum is well represented by the results of the generic normal form model for a noisy and weakly nonlinear limit cycle, with parameters all determined by observations. Using this model as a null case, we show here that all local peaks with enhanced power, apart from the 11-year band, are consistent with realization noise. Even a 3σ peak is expected to occur with a probability of about 0.25 at least once among the 216 period bins resolved by the cosmogenic isotope data. This casts doubt upon interpretations of such peaks in terms of intrinsic periodicities of the solar dynamo process.


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