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| Titel |
Re-thinking the record: Short-term downwash of Be-7 and Pb-210 in a Swedish peat bog |
| VerfasserIn |
Sophia Hansson, James Kaste, Carolina Olid, Richard Bindler |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250073609
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| Zusammenfassung |
| The past decade has seen a rapid increase in interest in the biogeochemical record preserved in peat, particularly as it relates to carbon dynamics and environmental changes. However, we still lack a complete understanding of the basic biogeochemical processes and their effect on trace element distributions. Are peat archives an absolute or relative record? What temporal resolution is realistic to interpret by using peat cores? By analyzing atmospherically deposited 210Pb, 137Cs, 241Am and 7Be as well as the trace metals Pb and Hg, in triplicate peat cores from an ombrotrophic Swedish bog we addressed two fundamental issues; the question of representativity of single cores and the incorporation of atmospheric signals in the peat. Both of these issues are of great importance and need to be considered when using peat cores as natural archives. By specifically including the short-lived tracer 7Be (T½ 53.4 days) we tested the hypothesis that downwashing of atmospherically-supplied elements may occur in well aerated peat. Our 210Pb activities all showed a non-monotonic decrease with depth suggesting some downward transport of 210Pb by percolating rainwater. Further to this, the activities of 7Be were detected to 20, 18 and 8 cm depth and there was a lack of any clear peaks in 241Am activities, which together indicate a smearing of the radionuclides to or at the water table. We conclude that this is compelling evidence for a rapid downwash of atmospherically supplied elements in peat, which extends down to the height of water table. By comparing our records to biomonitoring- and direct deposition data we were able to quantify the implications of this downwash on estimates of peat mass accumulation rates and metal (Pb and Hg) deposition. It is clear that under specific conditions the usage of a conventional CRS-dating model can lead to severe overestimations of peat mass accumulation as well as inaccurate estimations of past deposition. However, by applying a new correction model which includes a downward transport term, thereby adjusting the conventional CRS model, we suggest that this downward mobility can be successfully incorporated into age-depth models, allowing more accurate estimations of past deposition and peat accumulation. |
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