Paper No. 1
Presentation Time: 8:00 AM


WILLENBRING, Jane, Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104,

Although the very presence of soil within a landscape attests to faster net soil formation processes than the denudation processes over long timescales, long-term rates of soil production and weathering and erosion may also be determined by geochemical methods such as measurements of recalcitrant element abundances and terrestrial in situ cosmogenic nuclides, like beryllium-10(10Be). These tools have led to nothing less than a revolution in our understanding of rates of landscape change and surface processes. Recently, applications of the fallout cosmogenic nuclide 10Be coupled with stable beryllium-9 (9Be) have seen resurgence because of the relatively high production rate of 10Be in the atmosphere and the sorption of both nuclides to fine grained particles. While meteoric 10Be percolates into the soil from an atmospheric origin, 9Be is present in silicate minerals. Dissolved 9Be is released via weathering and either adsorbed to clays and mineral surface coatings or remains in the dissolved phase in pore water. Together, this nuclide pair becomes a very powerful tool; the details, caveats and applications for this new technique are just now being realized [1]. Using coupled 9Be and 10Be, we can now track the movement of fine-grained sediments within suspended load over a hydrograph and we can normalize the concentrations for complicating factors, such as grain-size differences, via adsorbed 9Be. Because lakes and other depo-centers contain time series records of fine-grained sediment, we may be able to elucidate erosion patterns from landscapes that are now gone though these records may be difficult to unravel [2]. We may even be able to trace the global silicate weathering cycle over the last 20 million years using time series 10Be/9Be ratios in ocean records (e.g. [3]) that act as faithful recorders of past ocean water chemistry for understanding ancient global weathering rates and processes.

[1] Willenbring, J.K. & von Blanckenburg, F. (2010a) Earth Sci. Rev. 98.

[2] Granger, D., Lifton, N., Willenbring, J.K. (2013) Geol. Soc. Amer. Bull.

[3] Willenbring, J.K. & von Blanckenburg, F. (2010b) Nature 465.