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

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.