Global Perturbation of the Carbon Cycle at the Onset of the Miocene Climatic Optimum

Abstract:

The processes driving high-amplitude climate variability and sustaining global warmth during the Miocene climatic optimum (~17-14.7 Ma) are highly enigmatic. We present high-resolution benthic and bulk carbonate isotope records in an exceptional sedimentary archive (Integrated Ocean Drilling Program Site U1337, eastern equatorial Pacific Ocean), which offer a new view of climate evolution over the onset of the climatic optimum. A sharp decline in benthic and bulk carbonate δ¹⁸O and δ¹³C at ~16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrates that abrupt climate warming was coupled to an intense perturbation of the carbon cycle. We conclude that elevated atmospheric pCO₂ acted as an amplifier of climate variability after 16.9 Ma, driving profound changes in the global carbon reservoir. Comparison with a high-resolution δ¹³C record spanning the onset of the Cretaceous Oceanic Anoxic Event 1a (~120 Ma ago) reveals common forcing factors and climatic responses during two unusually warm episodes of Earth’s history with widely differing boundary conditions: the virtually ice-free Cretaceous “Super Greenhouse” and the Miocene “Icehouse” with dominant Southern Hemisphere ice cover. In both periods, rapid CO₂ addition to the atmosphere induced abrupt climate warming and drove fundamental changes in the carbon cycle that were only mitigated over long timescales (>100 kyr). Despite obvious differences with the modern ocean/climate system, these results provide a useful perspective to evaluate future climate impacts in response to anthropogenic CO₂ rise.