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| Titel |
Six centuries of annually resolved 10Be in varved lake sediments and its relation to production rates |
| VerfasserIn |
Ann-Marie Berggren, Ala Aldahan, Göran Possnert, Eeva Haltia-Hovi, Timo Saarinen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040770
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| Zusammenfassung |
| A relatively short atmospheric residence time of a few months to one year, combined with a
simple chemistry with only one charge state and a lack of anthropogenic sources, has made
10Be a vital source of information about past variability in solar activity, cosmic rays and
geomagnetic field intensity. Because these forces affect the cosmogenic isotope production
rate, past variations can be traced and timed by measuring 10Be in well-dated archives,
among which are ice and sediment cores. Annually resolved terrestrial 10Be archives other
than polar ice sheets are a hereto unexplored source of past solar activity and climate
information, the main impediment being difficulties in finding natural archives that allow for
annual sampling with sufficient 10Be for AMS (accelerator mass spectrometry)
measurements.
Cosmogenic isotope production is geographically unevenly distributed, and despite
subsequent atmospheric mixing, atmospheric circulation patterns and deposition pathways
may cause local or regional variations of 10Be deposition. Although ice cores from Greenland
and Antarctica have provided interesting data, a lack of annually resolved 10Be
data from sediment archives represents a hindrance against exploring the nature
of 10Be signals in regions other than polar. Varved lake sediments are potential
targets for this purpose, with sufficient temporal resolution to reveal whether the
sediment 10Be signal reflects production variations driven by the 11-year Schwabe
solar cycle, or whether it is more controlled by local catchment parameters on this
timescale.
Here we report for the first time annual distribution of 10Be in varved sediments, from a
lake situated at 63.6Ë N, 29.1Ë E, 96 m a.s.l. The focus on the last 600 years provides an
unprecedented opportunity for comparison of sediment 10Be data with annual ice core,
neutron monitor and sunspot number data. The results indicate successful recovery of 10Be
atoms from as little as 20 mg sediment, with average concentrations of 4Ã108 atoms g-1.
Deposition rates were determined using sediment accumulation rates and the size of the
catchment area, and the range of 0.6-3.5Ã106 atoms cm-2 a-1 agrees with modelled values
in literature and earlier lake sediment findings. Several periods of raised 10Be deposition were
identified and can be matched to periods of low solar activity, such as during the
Maunder and Spörer grand solar minima. We observe relatively high 10Be values
during some years, a variability which has also been recognized in ice core 10Be
records. This may relate to atmospheric transport and deposition processes, but in our
case peaks may also indicate infrequent pulses of 10Be from the catchment area. |
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