Technical Note: Altitude scaling of ³⁶Cl production from Fe

Abstract. Cosmogenic nuclide production rates depend on the excitation functions of the underlying nuclear reactions and the intensity and energy spectrum of the cosmic ray flux. The cosmic ray energy spectrum shifts towards lower average energies with decreasing altitude such that production from high-energy reactions may attenuate more rapidly in the atmosphere than other reactions and require unique scaling factors. Here, we assess the possibility of unique scaling of ³⁶Cl production from Fe by modeling changes in the ³⁶Cl_Fe/³⁶Cl_K and ³⁶Cl_Fe/¹⁰Be_qtz production ratios with altitude. We evaluate model predictions against measured ³⁶Cl concentrations in magnetite and K-feldspar and ¹⁰Be concentrations in quartz from granitic rocks exposed across an elevation transect (ca. 1700–4300 m asl) in western North America. The data are broadly consistent with model predictions. The null hypothesis, that production ratios are invariant with altitude, can be rejected at the 90 % confidence level. We recommend using reaction-specific scaling factors for scaling ³⁶Cl production in magnetite and other Fe-rich minerals.