1. Source: Stewart et al., 2001

2. Strontium vs. Calcium Both are alkaline earth elements with +2 valence charge Strontium –Atomic number = 38 –Ionic Radius = 1.18 angstroms Calcium –Atomic number = 20 –Ionic Radius = 1.00 angstroms

3. Source: Kennedy et al., 2002

4. Source: Capo et al., 1998

7. Strontium Isotope System Indicator of both age and geochemical origin –Older rocks with same initial Rb/Sr will have higher 87 Sr/ 86 Sr than younger ones. –Rocks of a given age composed of different minerals will show differentiation in strontium ratios –The combination of these factors allows strontium to be used a tracer of cation source

8. Source: Capo et al., 1998

9. Strontium as a Tracer of Soil Cation Source: Weathering vs. Atmospheric Deposition Mass Balance – Two Member Mixing Must have sufficient difference between the two end members Must assume steady-state weathering or use more complex models to simulate changes in end members

10. Source: Bullen et al., 1997

11. Source: White et al., 1999

12. Source: Blum et al., 2002

13. Source: Kennedy et al., 2002

15. Figure 2: Location of proposed field sites in the San Juan Mountains in relation to the western US deserts. Field Sites

17. 87/86 Sr 143/144 Ndε Nd Surface rocks0.707397 (0.000013)0.512216-8.23 Dust Events April 1, 20050.720471 (0.000013)0.512089-10.71 April 4, 20050.716402 (0.000012)0.512084-10.81 April 8, 20050.714878 (0.000009)0.512104-10.42 May 9, 20050.713525 (0.000007)0.512103-10.44

20. Source: Chadwick et al., 1999

21. Source: Stewart et al., 2001