Oligocene atmospheric CO2 drawdown linked to increased land surface weatherability

Abstract

The Oligocene features a long-term decrease in atmospheric CO₂ levels (pCO₂). However, the driving force of the Oligocene pCO₂ drawdown remains uncertain. Here, we examine the response of silicate chemical weathering to the Oligocene Asian monsoon enhancement in the tectonically active Tibetan Plateau. On tectonic timescales, the silicate weathering rate is elevated in high-weatherability catchments caused by intensive erosion. On orbital timescales, the degree of silicate alteration displays 405-kyr eccentricity cycles, with amplified oscillations corresponding to a vigorous hydrological cycle. Our geologic records, for the first time, reveal that the strength of silicate weathering feedback and CO₂ consumption have increased in a setting of high land surface weatherability. Given the increase in global erosion rate during the Oligocene, the consequent increase in land surface weatherability and weathering feedback strength may modulate the pCO₂ decrease.