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| 2. |
- Aldahan, Ala, et al.
(författare)
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Atmospheric impact on beryllium isotopes as solar activity proxy
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:L21812
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Tidskriftsartikel (refereegranskat)abstract
- Reconstructing solar activity variability beyond the time scale of actual measurements provides invaluable data for modeling of past and future climate change. The 10 Be isotope has been a primary proxy archive of past solar activity and cosmic ray intensity, particularly for the last millennium. There is, however, a lack of direct high-resolution atmospheric time series on 10 Be that enable estimating atmospheric modulation on the production signal. Here we report quasi-weekly data on 10 Be and 7 Be isotopes covering the periods 1983-2000 and 1975-2006 respectively, that show, for the first time, coherent variations reflecting both atmospheric and production effects. Our data indicate intrusion of stratosphere/upper troposphere air masses that can modulate the isotopes production signal, and may induce relative peaks in the natural 10 Be archives (i.e., ice and sediment). The atmospheric impact on the Be-isotopes can disturb the production signals and consequently the estimate of past solar activity magnitude. Citation: Aldahan, A., J. Hedfors, G. Possnert, A. Kulan, A.-M. Berggren, and C. Soderstrom (2008), Atmospheric impact on beryllium isotopes as solar activity proxy, Geophys. Res. Lett., 35, L21812, doi: 10.1029/2008GL035189.
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| 3. |
- Berggren, Ann-Marie, 1969-, et al.
(författare)
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10Be and solar activity cycles in varved lake sediments, AD 1900–2006
- 2010
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:2, s. 559-569
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Tidskriftsartikel (refereegranskat)abstract
- Annually resolved terrestrial 10Be archives other than those in polar ice sheets are heretofore unexplored sources of information about past solar activity and climate. Until now, it has proven difficult to find natural archives that have captured and retained a 10Be production signal, and that allow for annual sampling and contain sufficient 10Be for AMS measurement. We report the first annually resolved record of 10Be in varved lake sediments. The record comes from Lake Lehmilampi, eastern Finland, which lies at 63°37′N, 29°06′E, 95.8 m a. s. l. The focus on the last 100 years provided an unprecedented opportunity to compare sediment 10Be data with annual ice core, neutron monitor and sunspot number data. Results indicate successful recovery of 10Be atoms from as little as 20 mg sediment. Sediment 10Be accumulation rates suggest control by solar activity, manifested as a reflection of the 11-year Schwabe solar cycle and its amplitude variations throughout the investigated period. These results open the possibility of using varved lake sediment 10Be records as a new proxy for solar activity, thus providing a new approach for synchronization of paleoclimate events worldwide.
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| 4. |
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| 5. |
- Berggren, Ann-Marie, 1969-, et al.
(författare)
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A 600-year annual 10Be record from the NGRIP ice core, Greenland
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36, s. L11801-
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Tidskriftsartikel (refereegranskat)abstract
- Despite the extensive use of 10Be as the most significant information source on past solar activity, there has been only one record (Dye-3, Greenland) providing annual resolution over several centuries. Here we report a new annual resolution 10Be record spanning the period 1389-1994 AD, measured in an ice core from the NGRIP site in Greenland. NGRIP and Dye-3 10Be exhibits similar long-term variability, although occasional short term differences between the two sites indicate that at least two high resolution 10Be records are needed to assess local variations and to confidently reconstruct past solar activity. A comparison with sunspot and neutron records confirms that ice core 10Be reflects solar Schwabe cycle variations, and continued 10Be variability suggests cyclic solar activity throughout the Maunder and Spörer grand solar activity minima. Recent 10Be values are low; however, they do not indicate unusually high recent solar activity compared to the last 600 years.
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| 7. |
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| 8. |
- Berggren, Ann-Marie, 1969-, et al.
(författare)
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Enhanced beam currents with co-precipitated niobium as a matrix for AMS measurements of 10Be
- 2010
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 268:7-8, s. 795-798
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Tidskriftsartikel (refereegranskat)abstract
- When dealing with small amounts of 10Be, it is challenging to achieve the good performance in the ion source that is needed to enable a reliable AMS measurement. We have co-precipitated beryllium with dissolved NbCl5, using a range of mixing ratios, to establish an optimal and practical procedure. 9Be16O‑ beam currents for co-precipitated samples of 9Be-Nb are often higher, but show a slower rise than for samples either co-precipitated or mixed with silver. However, while the Ag sample currents soon deteriorate, Nb sample currents stay high for an extended time, leading to higher measuring performance and better statistics. Although co-precipitated Be-Nb mixtures do not reach such high beam currents as BeO mechanically mixed with Nb powder, we prefer co-precipitation as it provides enough material for handling and an additional mixing step is avoided. We recommend use of NbCl5 as an alternative to AgNO3 on account of the much lower boron association of niobium compared to silver. No critical limit in the matrix:Be mixing ratio was observed, but we note a steady decline of maximum currents reached with increasing mixing ratio.
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| 9. |
- Berggren, Ann-Marie, 1969-
(författare)
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Influence of solar activity and environment on 10Be in recent natural archives
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the link between the Sun and climate is vital in the current incidence of global climate change, and 10Be in natural archives constitutes an excellent tracer for this purpose. As cosmic rays enter the atmosphere, cosmogenic isotopes like 10Be and 14C are formed. Variations in solar activity modulate the amount of incoming cosmic rays, and thereby cosmogenic isotope production. Atmospherically produced 10Be enters natural archives such as sediments and glaciers by wet and dry deposition within about a year of production. 10Be from natural archives therefore provides information on past solar activity, and because these archives also contain climate information, solar activity and climate can be linked. One remaining question is to what degree 10Be in natural archives reflects production, and to what extent the local and regional environment overprints the production signal. To explore this, 10Be was measured at annual resolution over the last 600 years in a Greenland ice core. Measurement potentials for these samples benefited from the development of a new laboratory method of co-precipitating 10Be with niobium. To diversify geographic location and archive media type, a pioneer study of measuring 10Be with annual resolution in varved lake sediments from Finland was conducted, with samples from the entire 20th century. Pathways of 10Be into lake sediments are more complex than into glacial ice, inferring that contemporary atmospheric conditions may not be recorded. Here, it is shown for the first time that tracing the 11-year solar cycle through lake sediment 10Be variations is possible. Results also show that on an annual basis, 10Be deposition in ice and sediment archives is affected by local environmental conditions. On a slightly longer timescale, however, diverse 10Be records exhibit similar trends and a negative correlation with solar activity. Cyclic variability of 10Be deposition persisted throughout past grand solar minima, when little or no sunspot activity was recorded. 10Be levels indicate that although solar activity has been high during the 20th century, levels are not unprecedented in the investigated 600 years. Aerosol 10Be/7Be values indicate possible influence of stratosphere-troposphere exchange on isotope abundance and the production signal.
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| 10. |
- Berggren, Ann-Marie, et al.
(författare)
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Linking ice sheet and lake sediment archives of Be-10, 1468-1980 CE
- 2013
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 294, s. 524-529
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Tidskriftsartikel (refereegranskat)abstract
- As part of understanding and reconstructing our climate history it is important to investigate the link between climate and solar activity. Ice cores and ocean sediments have provided information on a range of timescales on atmospheric Be-10 production, which is a proxy for past solar activity due to its cosmogenic nature of production. We here present results from the first, to our knowledge, multi-centennial and annual resolution study of Be-10 in varved lake sediments. Varves were sampled over an interval covering the period 1468-2006 CE in sediment cored from Lake Lehmilampi in eastern Finland. The measured concentrations were converted into annual Be-10 deposition rates by using the weights of dried samples as an estimation of sedimentation rates and scaling the result from sampling to catchment area size. We compare the lake catchment Be-10 deposition rates to those derived from the Greenlandic ice cores NGRIP and Dye-3 along with past solar activity. Sediment Be-10 concentrations range 2.1-17.6 x 10(8) atoms g(-1). The high end of this range is represented by a limited number of samples, and the average is near the lower end at 4.1 x 10(8) atoms g(-1). The deposition rates range 0.5-3.9 x 10(6) atoms cm(-2) year(-1), with an average of 1.8 x 10(6) atoms cm(-2) year (0.057 atoms cm(-2) s(-1)). We note higher Be-10 deposition during the Sporer (similar to 1415-1535 CE) and Maunder (similar to 1645-1715 CE) solar minima, and also at the onset of the Dalton (similar to 1790-1830 CE) minimum. Equally high Be-10 values in the 1840s and lower deposition during the Dalton minimum are not consistent with contemporaneous solar activity. Although this may in part be a result of incomplete measurements in the 19th century, it also shows the complexity of deposition and the intricacy of reconstructing past solar activity from sediment Be-10 data. A comparison with ice core data reveals particularly good agreement between sediment and Dye-3 Be-10 flux around 1500-1750 CE.
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