| 1. |
- Adolphi, Florian, et al.
(author)
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Intercomparison of C-14 Dating of Wood Samples at Lund University and Eth-Zurich Ams Facilities: Extraction, Graphitization, and Measurement
- 2013
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In: Radiocarbon. - 0033-8222. ; 55:2-3, s. 391-400
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Journal article (peer-reviewed)abstract
- We conducted an interlaboratory comparison between our radiocarbon-related research group at Lund University and the established ETH-Zurich facility to test the quality of the results obtained in Lund and to identify sources of potential background differences and scatter. We did find differences between the 2 laboratories in the contributions of chemical preparation, graphitization, and measurements to the overall background. The resulting overall background is, however, almost similar. Multiple measurements on 2 wood samples of known calendar age yield consistent and accurate C-14 ages in both laboratories. However, one of our known samples indicates that IntCal09 is similar to 38 +/- 16 C-14 BP too young at 7020 calendar yr BP, which is consistent with one of the raw data sets contributing to IntCal09. Overall, our results show that a systematic approach to compare the different steps involved in C-14 age determination is a useful exercise to pinpoint targets for improvement of lab routines and assess interlaboratory differences. These effects do not necessarily become apparent when comparing C-14 measurements that integrate over the whole process of preparation and measurement of different laboratories.
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| 2. |
- Adolphi, Florian, et al.
(author)
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Persistent link between solar activity and Greenland climate during the Last Glacial Maximum
- 2014
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In: Nature Geoscience. - 1752-0908 .- 1752-0894. ; 7:9, s. 662-666
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Journal article (peer-reviewed)abstract
- Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates(1). Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as Be-10 and C-14 from ice cores and tree rings(2,3). Here we present a high-resolution Be-10 record from the ice core collected from central Greenland by the Greenland Ice Core Project (GRIP). The record spans from 22,500 to 10,000 years ago, and is based on new and compiled data(4-6). Using C-14 records(7,8) to control for climate-related influences on Be-10 deposition, we reconstruct centennial changes in solar activity. We find that during the Last Glacial Maximum, solar minima correlate with more negative delta O-18 values of ice and are accompanied by increased snow accumulation and sea-salt input over central Greenland. We suggest that solar minima could have induced changes in the stratosphere that favour the development of high-pressure blocking systems located to the south of Greenland, as has been found in observations and model simulations for recent climate(9,10). We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.
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| 3. |
- Adolphi, Florian
(author)
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Solar Activity Changes at the End of the Last Ice Age - Influences on Climate and Applications for Dating
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- Throughout its history Earth experienced a variety of natural climate changes. By investigating their spatial and temporal evolution we can increase the understanding of the mechanisms and dynamics underlying natural climate change and improve our general comprehension of the climate system. Prerequisites of these investigations are reliable reconstructions of past forcing variations as well as sound and consistent chronologies of paleoclimate records. The Sun is by far Earth’s most important source of energy and variations in its irradiance have been shown to influence climate on different temporal and spatial scales. The exact mechanisms of these solar influences on climate are, however, not fully understood. Variations in solar activity also cause changes in the atmospheric production rates of cosmogenic radionuclides, such as 10Be and 14C. These radionuclides get subsequently deposited in various environments which can, hence, provide information about past solar activity levels. Furthermore, these records can be synchronized to each other by identifying coherent production rate related patterns in their radionuclide records. This project aims to extend solar activity reconstructions back into the late glacial and investigate potential sun-climate relationships. Furthermore, the consistency of the time scales underlying different records is tested by comparing their cosmogenic radionuclide records. In addition, it aims to improve radiocarbon dating calibration by extending its tree-ring based section further back in time. We present the first solar activity reconstruction for the late glacial based new and published 10Be data from the GRIP and GISP2 ice cores, supported by published 14C data. We infer that late glacial and Holocene solar activity variations have been comparable in both patterns and amplitudes. We find a persistent influence of solar activity changes on Greenland climate during the Last Glacial Maximum which appears coherent with modern day observations and climate model results. This suggests that a similar solar forcing mechanism may have been operating under otherwise very different climate regimes. We propose a time scale transfer function between Greenland ice core and radiocarbon dated records by synchronizing the temporal variations of ice core 10Be and tree-ring 14C records. We outline a statistical framework that allows time scale differences and uncertainties to be inferred. We find that there is a continuously growing difference between Greenland ice core and radiocarbon based chronologies throughout the Holocene. Furthermore, we identify a rapid shift in this time scale difference around 12,500 years ago, that cannot be explained with ice core layer counting uncertainties alone. Instead, we propose that this effect may arise from uncertainties in the absolute dating of tree-ring records. We present new 14C data on floating tree-ring chronologies that can improve radiocarbon dating calibration between 14,000 to 14,700 years ago. We introduce a method of how combined information from 14C and 10Be records can aid us to infer absolute ages for these chronologies. These new records add substantial structure to the calibration curve and we note that missing this structure can lead to erroneous calibration of 14C dates by up to 500 years.
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| 4. |
- Muscheler, Raimund, et al.
(author)
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Assessing the differences between the IntCal and Greenland ice-core time scales for the last 14,000 years via the common cosmogenic radionuclide variations
- 2014
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 106, s. 81-87
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Journal article (peer-reviewed)abstract
- Variations in galactic cosmic rays reaching the Earth's atmosphere produce globally synchronous variations in the production rates of cosmogenic radionuclides. In consequence, they leave their imprint in tree-ring 14C and ice-core 10Be records. By identifying this signal and correcting for the known geochemical influences on the radionuclides, it is possible to compare and synchronize the tree-ring chronology and the Greenland ice-core time scale. Here, we compare the IntCal13 and the GICC05 time scales for the last 14,000 years via identification and synchronization of the common short-term variations in the ice-core 10Be and tree-ring 14C records most likely induced by variations in the solar modulation of galactic cosmic rays. We conclude that systematic time-scale differences have to be accounted for if ice-core and 14C-dated records are compared on decadal time scales. These are mostly within the uncertainties of the time scales and the method proposed here. However, for large parts of the mid to late Holocene (i.e. after 7000 yrs BP) the best agreement between ice-core 10Be and tree-ring 14C records is obtained for time shifts outside the stated errors of the respective time scales. A transfer function is proposed that can be applied to synchronize the GICC05 ice-core time scale to the radiocarbon time scale.
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| 5. |
- Muscheler, Raimund, et al.
(author)
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Challenges in C-14 dating towards the limit of the method inferred from anchoring a floating tree ring radiocarbon chronology to ice core records around the Laschamp geomagnetic field minimum
- 2014
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In: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 394, s. 209-215
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Journal article (peer-reviewed)abstract
- The C-14 dating method is the cornerstone for inferring age estimates for natural archives covering the last 50 000 yrs. However, C-14 age calibration for the last ice age relies mostly on records that only indirectly reflect the atmospheric C-14 concentrations. In consequence, calendar age estimates are significantly more uncertain for the period of the last ice age compared to the past 14000 yrs where tree-ring based calibration records exist. Here we connect a C-14 tree-ring chronology from Kauri trees in New Zealand to ice core Be-10 records via the common signal in the galactic cosmic ray flux around the period of the Laschamp geomagnetic field minimum (ca. 41 000 yrs BP). Synchronous changes of modelled C-14 and C-14 inferred from U/Th-dated speleothems support the ice core chronology independently and suggest that the published ice core time scale errors are rather conservative for this period. Our analysis puts C-14 age determinations directly into the context of ice core climate records and it shows that the C-14 records underlying the C-14 calibration curve overestimate the atmospheric C-14 concentration by more than 200 parts per thousand. Consequently, C-14 age calibration presently yields too old calendar age estimates by about 1200 yrs for this period. (C) 2014 Elsevier B.V. All rights reserved.
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