『Abstract
Rainfall scavenges meteoric cosmogenic 10Be from the
atmosphere. 10Be falls to the Earth's surface, where
it binds tightly to sediment particles in non-acidic soils over
the life-span of those soils. As such, meteoric 10Be
has the potential to be an excellent geochemical tracer of erosion
and stability of surfaces in a diverse range of natural settings.
Meteoric 10Be has great potential as a recorder of
first-order erosion rates and soil residence times. Even though
this tracer was first developed in the late 1980s and showed great
promise as a geomorphic tool, it was sidelined in the past two
decades with the rise of the “sister nuclide”, in situ 10Be,
which is produced at a known rate inside quartz minerals. Since
these early days, substantial progress has been made in several
areas that now shed new light on the applicability of the meteoric
variety of this cosmogenic nuclide. Here, we revisit the potential
of this tracer and we summarize the progress: (1) the atmospheric
production and fallout is now described by numeric models, and
agrees with present-day measurements and paleo-archives such as
from rain and ice cores; (2) short-term fluctuations in solar
modulation of cosmic rays or in the delivery of 10Be
are averaged out over the time scale soils accumulate; (3) in
many cases, the delivery of 10Be is not dependent on
the amount of precipitation; (4) we explore where 10Be
is retained in soils and sediment; (5) we suggest a law to account
for the strong grain-size dependence that controls adsorption
and the measured nuclide concentrations; and (6) we present a
set of algebraic expressions that allows calculation of both soil
or sediment ages and erosion rates from the inventory of meteoric
10Be distributed through a vertical soil column. The
mathematical description is greatly simplified if the accumulation
of 10Be is at a steady state with its export through
erosion. In this case, a surface sample allows for the calculation
of an erosion rate. Explored further, this approach allows calculation
of catchment-wide erosion rates from river sediment, similar to
the approach using 10Be produced in situ. In contrast
to the in situ 10Be approach, however, these analyses
can be performed on any sample of fine-grained material, even
where no quartz minerals are present. Therefore, this technique
may serve as a tool to date sediment where no other chronometer
is available, to track particle sources and to measure Earth-surface
process rates in soil, suspended river sediment, and fine-grained
sedimentary deposits.
Keywords: cosmogenic; meteoric; Beryllium; denudation; sediment;
erosion; geomorphology 』
Contents
1. Introduction
2. Principles of the meteoric 10Be tracer
2.1. Quantifying the atmospheric flux
2.1.1. Production
2.1.2. Delivery
2.2. Dust
2.3. Retentivity
2.3.1. Speciation
2.3.2. Adsorption characteristics in soil
2.3.3. 10Be in plant litter and sediment rich in
organic carbon
2.3.4. 10Be distribution with depth
2.3.5. Grain size
2.3.6. Chronosequences
2.3.7. Partition coefficients
2.3.8. Watershed mass balances
2.4. Soil ages from an inventory of 10Be
2.5. Erosion rates from an inventory of 10Be]
2.6. Erosion rates from surface soil concentrations and spatially-averaged
erosion rates from meteoric 10Be adsorbed to river
sediment
3. Method caveat, future applications and prerequisites
4. Conclusions
Acknowledgements
References