This video simulates the Be-10 accumulation in a depth profile affected by:
- Soil formation: this modifies the density under the surface.
- Bioturbation: plants and animals that mix the top layer of the soil (~20cm).
- Sustainable agriculture: mixing the top ~50 cm of soil, but not eroding the surface faster than the rate at which the soil is formed.
- Unsustainable agriculture: mixing the top ~50 cm of soil, and eroding the surface much faster than the rate at which the soil is formed.
This model simulates the accumulation of Be-10 under a surface that is being eroded at a constant rate of 50 mm/ka:
- from t=0 to 50 ka, the density of the profile is constant
- from t=50 to 100 ka, the density of the profile changes to simulate soil in the upper 1.5m and saprolite until a depth of 3m. The profile is still in equilibrium: the soil production rate (SPR) is the same as the erosion rate at the top of the profile (both 50 mm/ka)
- from t=100 to 150 ka, the top 20 cm of the profile is affected by bioturbation, generating a mixing layer enriched in Be-10
- from t=150 to 200 ka, sustainable agriculture is simulated by a mixing layer of 50 cm
- from t=200 to 201 ka (last 1000 years), unsustainable agriculture is simulated by eroding the surface at a rate faster than the soil production rate (the profile is not in equilibrium!)
The effect of unsustainable agriculture is like a bulldozer that removes the top of the soil and mixes the first 0.5 m of the remaining soil.
Effect on Be-10-derived soil production rates
At the end of the video I have calculated the apparent soil production rate (a-SPR) from a sample taken in the saprolite (red star ).
The a-SPR is faster than the actual SPR (110 mm/ka vs. 50 mm/ka), but much slower than the erosion rate generated by unsustainable agriculture (~3000 mm/ka).
Also, a red line illustrates the Be-10 profile we would reconstruct from that sample using CoSOILcal, which matches well the actual Be-10 profile. This means that even taking several samples from this profile, we probably wouldn’t notice the break in the equilibrium generated by unsustainable agriculture.
You can find the code that generates this video in my GitHub repository Agriculture_10Be_simulator.