Accelerator mass spectrometry (AMS) dating of pollen concentrates is often used in lake sediment records where large, terrestrial plant remains are unavailable. Ages produced from chemically concentrated pollen as well as manually picked Pinaceae grains in Yellowstone Lake (Wyoming) sediments were consistently 1700-4300 cal years older than ages established by terrestrial plant remains, tephrochronology, and the age of the sediment-water interface. Previous studies have successfully utilized the same laboratory space and methods, suggesting the source of old-carbon contamination is specific to these samples. Manually picking pollen grains precludes admixture of non-pollen materials. Furthermore, no clear source of old pollen grains occurs on the deglaciated landscape, making reworking of old pollen grains unlikely. High volumes of CO2 are degassed in the Yellowstone Caldera, potentially introducing old carbon to pollen. While uptake of old CO2 through photosynthesis is minor (F14C approximately 0.99), old-carbon contamination may still take place in the water column or in surficial lake sediments. It remains unclear, however, what mechanism allows for the erroneous ages of highly refractory pollen grains while terrestrial plant remains were unaffected. In the absence of a satisfactory explanation for erroneously old radiocarbon ages from pollen concentrates, we propose steps for further study.
|Original language||English (US)|
|Number of pages||22|
|State||Published - Dec 3 2020|
Bibliographical noteFunding Information:
This research was supported by NSF Grant No. 1515353 to C. Whitlock and sampling in Yellowstone National Park was conducted under permits YELL-SCI-0009 and YELL-SCI-5054. Coring efforts at Yellowstone Lake were aided by M. Baker, S.R. Brown, D. Conley, S.C. Fritz, C. Linder, L.A. Morgan, R. O’Grady, W.C. Shanks III, M.D. Shapley, R.A. Sohn, and three anonymous Yellowstone National Park rangers. This project was greatly improved through conversations with J. Southon and S.R.H. Zimmerman and thoughtful reviews of the manuscript came from D. McWethy, L.A. Morgan, D.A. Orme, and W.C. Shanks III.
© 2020 by the Arizona Board of Regents on behalf of the University of Arizona.
- AMS dating
Continental Scientific Drilling Facility tags