Calibrating a long-term meteoric 10 Be delivery rate into eroding western US glacial deposits by comparing meteoric and in situ produced 10 Be depth profiles

Abstract. Meteoric 10 Be ( 10 Be met ) concentrations in soil profiles have great potential as a geochronometer and a tracer of Earth surface processes, particularly in fine-grained soils lacking quartz that would preclude the use of in situ produced 10 Be ( 10 Be in situ ). One prerequisite for using this technique for accurately calculating rates and dates is constraining the delivery, or flux, of 10 Be met to a site. However, few studies to date have quantified long-term (i.e., millennial) delivery rates, and none have determined a delivery rate for an eroding soil. In this study, we compared existing concentrations of 10 Be in situ with new measurements of 10 Be met in eroding soils sampled from the same depth profiles to calibrate a long-term 10 Be met delivery rate. We did so on the Pinedale ( ∼  21–25 kyr) and Bull Lake ( ∼  140 kyr) glacial moraines at Fremont Lake, Wyoming (USA), where age, grain sizes, weathering indices, and soil properties are known, as are erosion and denudation rates calculated from 10 Be in situ . After ensuring sufficient beryllium retention in each profile, solving for the delivery rate of 10 Be met , and normalizing for paleomagnetic and solar intensity variations over the Holocene, we calculate 10 Be met fluxes of 1.46 ( ± 0.20)  ×  10 6  atoms cm −2  yr −1 and 1.30 ( ± 0.48)  ×  10 6  atoms cm −2  yr −1 to the Pinedale and Bull Lake moraines, respectively, and compare these values to two widely used 10 Be met delivery rate estimation methods that substantially differ for this site. Accurately estimating the 10 Be met flux using these methods requires a consideration of spatial scale and temporally varying parameters (i.e., paleomagnetic field intensity, solar modulation) to ensure the most realistic estimates of 10 Be met -derived erosion rates in future studies.