Calibrating a long-term meteoric <sup>10</sup>Be delivery rate into Western US glacial deposits through a comparison of complimentary meteoric and in situ-produced <sup>10</sup>Be depth profiles

Abstract

Abstract. Meteoric 10Be (10Bemet) concentrations in soil profiles 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 10Be (10Bein situ). One prerequisite for using this technique for accurately calculating rates and dates is constraining the delivery, or flux, of 10Bemet to a site. However, few studies to date have quantified long-term (i.e. millennial) delivery rates. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in soils sampled from the same depth profiles to calibrate a long-term 10Bemet delivery rate. We did so on the Pinedale and Bull Lake glacial moraines at Fremont Lake, Wyoming (USA) where age, grain sizes, weathering indices, and soil properties are known, as are erosion/denudation rates calculated from 10Bein situ. After ensuring sufficient beryllium retention in each profile, solving for the delivery rate of 10Bemet via Monte Carlo simulations, and normalizing to Holocene-average paleomagnetic intensity, we calculate best-fit fluxes of 0.92 (+/− 0.08) × 106 and 0.71 (+0.09/−0.08) × 106 atoms cm−2 y−1 to the Pinedale and Bull Lake moraines, respectively, and compare these values to two widely-used 10Bemet delivery rate estimation methods. Accurately estimating 10Bemet flux using these methods requires careful consideration of spatial scale as well as temporally varying parameters (e.g. paleomagnetic field intensity) to ensure the most realistic estimates of 10Bemet-derived erosion rates in future studies.

Review

“…Line 34: Also Al-OOH (e.g. Graly et al, 2010) Line 43: I might avoid implying that most previous work is flawed here. These issues have been discussed and debated since the inception of the method with the work of Pavich and Monaghan.…”

“…The paper should flow naturally without the need to do this. Line 293: Graly et al 2010 tested this claim and found that grain size effects could explain subsurface maxima in none of the 29 soil profiles analyzed. A far better explanation is that 10Be is incorporated into the lattices of newly forming clays and oxyhydroxides at depth (e.g.…”

Response to Reviewer 1

“…Revised to "target nuclei" Line 34: Also Al-OOH (e.g. Graly et al, 2010 ) Revised to "Fe-and Al-oxyhydroxides", citation added Line 43: I might avoid implying that most previous work is flawed here. These issues have been discussed and debated since the inception of the method with the work of C4 Pavich and Monaghan.…”

“…After re-organization of sections as advised by both reviewers, we have greatly reduced section callouts throughout the manuscript. Line 293: Graly et al 2010 tested this claim and found that grain size effects could C8 explain subsurface maxima in none of the 29 soil profiles analyzed. A far better explanation is that 10Be is incorporated into the lattices of newly forming clays and oxyhydroxides at depth (e.g.…”