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

Abstract

Abstract. Meteoric 10Be (10Bemet) 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 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, and none have determined a delivery rate for an eroding soil. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in eroding soils sampled from the same depth profiles to calibrate a long-term 10Bemet 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 10Bein situ. After ensuring sufficient beryllium retention in each profile, solving for the delivery rate of 10Bemet, and normalizing for paleomagnetic and solar intensity variations over the Holocene, we calculate 10Bemet fluxes of 1.46 (±0.20) × 106 atoms cm−2 yr−1 and 1.30 (±0.48) × 106 atoms cm−2 yr−1 to the Pinedale and Bull Lake moraines, respectively, and compare these values to two widely used 10Bemet delivery rate estimation methods that substantially differ for this site. Accurately estimating the 10Bemet 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 10Bemet-derived erosion rates in future studies.

Deposition and retention of meteoric 10Be in Holocene Taiwan river terraces

“…We measured 10 Be and 9 Be concentrations in three river terraces of Taiwan Island, in order to quantify deposition and retention processes of meteoric 10 Be in Holocene archives. Compared to previous efforts on estimation of the long-term 10 Be depositional flux (Clow et al, 2020;Dixon et al, 2018;Ouimet et al, 2015;Reusser et al, 2010), the terraces of this study have the deepest sampling depths (e.g. 5.8-6.2 m) and youngest ages (<10 ka).…”

“…In terrace CB we model the variations in 10 Be depositional flux as a function of eroded soil thickness (Fig. 7) following a strategy similar to Clow et al (2020). To constrain the 10 Be concentration in the eroded surface soil ([ 10 Be]surface), two scenarios are considered here:…”

“…Even though in quite a few studies meteoric 10 Be was measured in soil (e.g. Bacon et al, 2012;Jungers et al, 2009;Mckean et al, 1993), most of them aimed at exploring the vertical and lateral transport of 10 Be, and only very few studies estimated the depositional processes of 10 Be (Clow et al, 2020;Dixon et al, 2018;Ouimet et al, 2015;Reusser et al, 2010). This is because several prerequisites have to be met for determining site-specific 10 Be deposition fluxes using dated soil profiles: 1) Full retention of meteoric 10 Be since landform stabilization.…”

Effects of Global Geomagnetic Field Variations Over the Past 100,000 Years on Cosmogenic Radionuclide Production Rates in the Earth's Atmosphere

“…This study focuses on the production of meteoric cosmogenic nuclides throughout the multi‐millennial timescale, leaving aside effects of the long‐term, global geomagnetic field models on in situ nuclide production rates. Both types of nuclides (meteoric and in situ) are widely used as proxies of the past geomagnetic field and solar variability, tracers of Earth surface processes, and as chronological tools (e.g., Clow et al., 2020; Simon et al., 2020; Willenbring & von Blanckenburg, 2010). Other nuclides can be considered as well, for instance, 3 H (Poluianov et al., 2020), which is widely used as a tracer of atmospheric and hydrological circulation.…”