Neogene continental denudation and the beryllium conundrum

Area of Science:

• Geochemistry
• Paleoclimatology
• Earth System Science

Background:

• Reconstructing Cenozoic continental silicate weathering is key to understanding Earth's carbon cycle and greenhouse gas history.
• Controversy exists regarding whether silicate weathering increased in the late Cenozoic, potentially triggering glacial cycles.
• Seawater beryllium isotopes have been interpreted as evidence for stable weathering rates, contrasting with other proxies.

Purpose of the Study:

• To investigate the role of beryllium isotopes in understanding late Cenozoic continental weathering rates.
• To reconcile discrepancies between beryllium isotope data and other proxies for weathering.
• To model the beryllium (Be) cycle and its implications for Earth's climate history.

Main Methods:

• Development and application of a Beryllium (Be) cycle model.
• Analysis of seawater ⁹Be and cosmogenic ¹⁰Be fluxes.
• Comparison of model outputs with existing geochemical proxies (Li, Sr, Os isotopes).

Main Results:

• Beryllium (Be) cycle model shows near-coastal scavenging counterbalances ⁹Be weathering flux variations.
• Seawater ¹⁰Be/⁹Be ratios remain stable despite large increases in denudation and weathering rates.
• ¹⁰Be/⁹Be records support an up to 11-fold increase in Be weathering and denudation rates in the late Cenozoic.

Conclusions:

• Beryllium isotopes, when modeled correctly, are consistent with a significant increase in continental weathering during the late Cenozoic.
• Increased CO₂ drawdown by weathering was likely offset by other geological processes, preventing extreme cooling.
• Potential counterbalancing processes include enhanced carbonate dissolution, organic carbon oxidation, and reduced basalt weathering.