 |
| Titel |
The influence of soil organic matter age spectrum on the reconstruction of atmospheric 14C levels via stalagmites |
| VerfasserIn |
Jens Fohlmeister, Bernd Kromer, Augusto Mangini |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035739
|
|
|
|
|
|
| Zusammenfassung |
| The imprint of the radiocarbon bomb peak was detected in the top of stalagmite ER-77
of Ernesto cave (north-western Italy). This recently grown stalagmite reveals a
reservoir age, also known as dead carbon fraction (dcf), of around  1050 14C years, or
12%. By applying a radiocarbon soil-karst model the age spectrum of soil organic
matter (SOM) as well as the CO2 contribution of the single SOM reservoirs to
the total soil CO2 can be derived. These parameters allow to calculate the recent
soil air CO2 radiocarbon activity. Under the assumption of constant vegetation,
meaning both vegetation density and the age spectrum of SOM, it is possible to
derive the soil air 14C activity of the past using the radiocarbon calibration curve
(IntCal04). Hence, we calculated an artificial stalagmite 14C record covering the last 25
thousand years with parameters determined for stalagmite ER-77. With this artificially
constructed record we derived the hypothetical atmospheric radiocarbon activity
by using the common method of applying a constant dcf on the 14C record of the
stalagmite.
This theoretical approach allows to analyse the impact of a constant and variable
SOM age spectrum on the deviations observed between the stalagmite-derived
atmospheric 14C activity and IntCal04. The deviations are larger for older SOM than for
younger SOM and change in time up to 2 pmC, depending on variations in the
atmospheric 14C level. This value is comparable with the 1-Ï uncertainty given
by IntCal04 for the last glacial. For a varying SOM age spectrum the deviations
between the stalagmite-derived atmospheric 14C activity and the calibration curve
exceed 3 pmC which is larger than the 1-Ï uncertainty of IntCal04. In general,
the SOM has smoothing, shifting and 14C depleting effects on the stalagmite 14C
record and, therefore, on the stalagmite-derived atmospheric 14C activity. In this
study changes in soil air pCO2 and carbonate dissolution conditions, which have
also an important impact on the 14C record of a stalagmite, are not accounted for. |
|
|
|
|
|
|