Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
10
26
21
3
L.
S CHOENBOHM
1 *, M.
K URZ
2 , R.
A CKERT J R .
3 , E.
B ROOK
4 , E.
B ROWN
5
1 Universiät Potsdam, Institut für Geowissenschaften, Postfach 60 15 53, 14415 Potsdam, Germany
2 WHOI, Woods Hole MA, USA
3 Harvard University, Cambridge, MA, USA
4 Washington State Universtiy, Vancouver, WA, USA
5 Large Lakes Observatory, Duluth, MN, USA
* Corresponding author ( lindsays@geo.uni-potsdam.de
)
We develop a new technique for determining an erosion history for a single site using depth dependent data for multiple cosmogenic nuclides, and apply this method in the Dry Valleys region of Antarctica. We present new 21 Ne and 3 He depth dependence data in quartz for sandstone bedrock cores (~1.25 m) collected from near the summit of Mt. Fleming and from a plateau above Arena Valley. Measured 21 Ne and 3 He attenuation lengths for the Mount Fleming core are 140
± 5 and 144 ± 7 g/cm 2 (1  ) respectively, similar to values determined for 10 Be and 26 Al in both cores in previous studies. 21 Ne and 3 He attenuation lengths for the Arena Valley core are significantly longer, 166 ± 3 and 196 ± 5 g/cm 2
(1  ) respectively. We attribute these exceptionally long attenuation lengths to the combined impacts of exposure history and nuclide production through muon interactions. The attenuation length of muon production is approximately an order of magnitude greater than that of neutron production. Higher erosion rates increase the proportion of total muonproduced cosmogenic nuclide in the near surface, thus increasing apparent attenuation length. We develop a modeling method to constrain both erosion history and muon production rate in quartz for 21 Ne and 3 He. We find that erosion rates at the Arena Valley site were higher in the past. Good fits to the data are obtained for moderate erosion rates (~1 m/Ma), persistent over several million years, followed by low erosion rate conditions for the last 1.3 Ma. Prolonged, low erosion rate conditions (< 1 m/Ma) punctuated by a short period of rapid erosion just prior to 1.3 Ma also produce good model fits to the data. Higher erosion rates prior to 1.3 Ma may reflect local conditions, but could also result from a regional shift in climate conditions in the Dry Valleys, with implications for the long-term stability of the East
Antarctic Ice Sheet. Modeling results also indicate muon production rates for 21 Ne and 3 He in quarts: P
-m
Ne=0.001 at/g/a and P
-m
He=0.16 at/g/a, SLHL.