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- Delmas, RJ, et al.
(författare)
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Bomb-test Cl-36 measurements in Vostok snow (Antarctica) and the use of Cl-36 as a dating tool for deep ice cores
- 2004
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509. ; 56:5, s. 492-498
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Tidskriftsartikel (refereegranskat)abstract
- A large pulse of atmospheric Cl-36 generated by a limited number of nuclear tests peaked in the late 1950s to early 1960s. The corresponding enhanced Cl-36 deposition is seen in various glaciological archives in the Northern Hemisphere. The profile of the bomb spike recorded in firn layers at Vostok Station, central East Antarctica. has been measured by employing accelerator mass spectrometry (AMS). The records obtained front two well-dated data sets collected in snow pits in 1997 and 1998 show a broad Cl-36 peak, beginning as early as the 1940s and reaching its maximum in the 1960s. The signal is followed by a long-lasting tail up to the surface. This pattern is totally unexpected. We show that the results, unlike the Greenland data, can be explained by a mobility of HCl in the Antarctic firn. This experiment demonstrates the instability of gaseous Cl- deposits. a phenomenon which has important implications for the use of natural cosmogenic Cl-36 radionuclides as a reliable dating tool for deep ice cores from low-accumulation areas. However, during glacial times, under favourable atmospheric chemistry conditions this dating method may still be applicable. Snow metamorphism and ventilation are assumed to be the two main physical processes responsible for the observed patterns.
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| 4. |
- Muscheler, Raimund, et al.
(författare)
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Causes and timing of the 8200 yr BP event inferred from the comparison of the GRIP Be-10 and the tree ring Delta C-14 record
- 2004
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:20-22, s. 2101-2111
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Tidskriftsartikel (refereegranskat)abstract
- We analyse the 8200 yr BP cold event by comparing the high-resolution Be-10 record from the GRIP ice core from Central Greenland with the well-known tree ring Delta(14)C record. By transferring the absolute dated tree ring chronology to the ice core time scale, we show that the coldest phase in the GRIP record occurred around 8150 yr BP. Furthermore, this method allows us to disentangle production and climate effects on Be-10 and C-14 with important implications for the reconstruction of past solar activity, and changes in the carbon cycle and Be-10 transport. We show that, in principle, it is possible to infer changes in ocean circulation by comparing Be-10 and C-14 records. However, the duration of the 8200 yr BP event is too short to assign unambiguously a significant change in atmospheric C-14 concentration to changes in the global ocean circulation. Based on the comparison of Be-10 with climate records, one could argue that the 8200 yr BP cold event is triggered by a change towards lower solar activity. However, this link is questioned by the fact that around this period there are other similar and even stronger changes in solar activity that have no apparent connection to climate changes. (C) 2004 Elsevier Ltd. All rights reserved.
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| 5. |
- Muscheler, Raimund, et al.
(författare)
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Changes in the carbon cycle during the last deglaciation as indicated by the comparison of Be-10 and C-14 records
- 2004
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Ingår i: Earth and Planetary Science Letters. - 1385-013X. ; 219:3-4, s. 325-340
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Tidskriftsartikel (refereegranskat)abstract
- The variations in atmospheric radiocarbon (C-14) concentration during the last 50 000 years can be attributed to changes in the C-14 production rate (due to changes in solar activity, the geomagnetic field and/or interstellar galactic cosmic ray flux) and to changes in the global carbon cycle. The relative contributions of these processes is the subject of current debate. Although the discrepancies between the various reconstructions of the past atmospheric radiocarbon concentration increase with age, the relatively good agreement over the last 25 000 years allows a quantitative discussion of the causes of the observed C-14 variations for this period. Using Be-10 measurements from Greenland Summit ice cores, we show that, in addition to solar and geomagnetically induced production rate changes, significant changes in the carbon cycle have to be considered to explain the measured C-14 concentrations. There is evidence that these changes are connected to: (1) global deglaciation and (2) climate changes in the North Atlantic region on centennial to millennial time scales related to changes in the ocean circulation. Differences between Be-10 and geomagnetic field records, however, suggest that uncertainties of about 20% still exist in determinations of past changes in the C-14 production rate. (C) 2004 Elsevier B.V. All rights reserved.
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