Discrepancy between long-term trends of the 10Be- and 14C-inferred radionuclide production rate: Likely reasons and implications
Final Report Abstract
After establishing customized, tracer‐calibrated models for radiocarbon (14C) and ice core beryllium‐10 (10Be), we investigated non‐production‐related changes of both cosmogenic radionuclides. In case of radiocarbon, our model results corroborate previous studies that the glacial‐interglacial drop in 14C by ca. 600‰ is only partly explicable by state‐of‐the‐art reconstructions of 14C production changes. However, our model based sensitivity studies point to a possible contribution by carbon cycle changes of only 100 ‰, which calls for a revision of the production scenarios, hitherto applied. Indeed, we find that the ice‐core‐10Be‐based reconstruction of 14C production changes from Muscheler et al. (2005) requires major revisions. Investigating non‐production related changes of ice core 10Be, we settled the understanding of the relevant transport and deposition processes of aerosol‐bound radionuclides in polar areas. (1) While the 10Be dry deposition flux may be used as proxy for the atmospheric 10Be inventory at dry Antarctic sites, our results show that the wet deposition flux may play a significant role in Greenland. Here, we find at Summit that total 10Be deposition is dominated by wet deposition, not only during Holocene but also during the relatively warm, last glacial interstadials. (2) Based on our long‐term polar radionuclide measurement programs and published atmospheric data, our model results point to a significant latitudinal dependence of solar and geomagnetic modulation of 10Be. Polar 10Be is less influenced by geomagnetic variations but more sensitive to solar activity changes than the global 10Be inventory. The relation between ice core 10Be and the global mean 10Be atmospheric production rate is thus non‐linear. Including this finding in our basic 10Be model approach, allowed for the first quantitative simulations of 10Be ice concentration records on the multi‐millennial time‐ scale. Application of 14C as tracer for long‐term carbon cycle dynamics requires a proper estimation of its production variability. Indeed ice core 10Be records may serve as proxy for these variations based on solar and geomagnetic changes. Within the here reported project we found that deficits in previous studies reporting on 10Be‐based cosmogenic production records result in deficient 14C model results.
Publications
- Continuous 25‐yr aerosol 7 10 210 records at coastal Antarctica. Part 2: variability of the radionuclides 7Be, 10Be and 210Pb. Tellus B, Vol. 63, 2011
Elsässer C., Wagenbach D., Weller R., Auer M., Wallner A., Christl M.
- Exploration of 10Be ice core records using a climatological model approach: Cosmogenic production versus climate variability. PhD thesis, Heidelberg University, 2013
- Simulating ice core 10Be on the glacial ‐ interglacial timescale. Clim. Past Discuss., 10, 761‐808, 2014
Elsässer C., Wagenbach D., Levin I., Stanzick A., Christl M., Wallner A., Kipfstuhl S., Seierstad I.K., Wershofen H., and Dibb J.
(See online at https://doi.org/10.5194/cpd-10-761-2014)
