Reply on RC1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> Here, we present cosmogenic ¹⁰Be and ³He data from Ferrar dolerite pyroxenes in surficial rock samples and a bedrock core from the McMurdo Dry Valleys, Antarctica, with the goal of refining the laboratory methods for extracting beryllium from pyroxene, further estimating the ¹⁰Be production rate in pyroxene, and demonstrating the applicability of the ¹⁰Be-³He in mafic rock. The ability to routinely measure cosmogenic ¹⁰Be in pyroxene will open new opportunities for quantifying exposure durations and Earth surface processes in mafic rocks. We describe scalable laboratory methods for isolating beryllium from pyroxene, which includes a simple hydrofluoric acid leaching procedure for removing meteoric ¹⁰Be, and the addition of a pH 8 precipitation step to reduce the cation load prior to ion exchange chromatography. ¹⁰Be measurements in pyroxene from the surface samples have apparent ³He exposure ages of 1&ndash;6 Ma. We estimate a spallation production rate for ¹⁰Be in pyroxene, referenced to ³He, of 3.6 &plusmn; 0.2 atoms g^&minus;1 yr^&minus;1. ¹⁰Be and ³He measurements in the bedrock core yield initial estimates for parameters associated with ¹⁰Be and ³He production by negative muon capture (<em>f</em>₁₀^*= 0.00183 and <em>f</em>₃^* <em>f_C</em> <em>f_D</em> = 0.00337). Next, we demonstrate that the ¹⁰Be-³He pair in pyroxene can be used to simultaneously resolve erosion rates and exposure ages, finding that the measured cosmogenic-nuclide concentrations in our surface samples are best explained by 2&ndash;8 Ma of exposure at erosion rates of 0&ndash;35 cm Myr^&minus;1. Finally, given the low ¹⁰Be in our laboratory blanks (average of 5.7 &times; 10⁴ atoms), the reported measurement precision, and our estimated production rate, it should be possible to measure 2 g samples with ¹⁰Be concentrations of 6 &times; 10⁴ atoms g^&minus;1 and 1.5 &times; 10⁴ atoms g^&minus;1 with 5 and 15% uncertainty, respectively. With this level of precision, Last Glacial Maximum to Late Holocene surfaces can now be dated with ¹⁰Be in pyroxene. Application of ¹⁰Be in pyroxene, alone or in combination with ³He, will expand possibilities for investigating glacial histories and landscape change in mafic rock.