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
2020
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.
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