Predominant orbital forcing on Asian hydroclimate linked with deep-sea records during the Miocene Climate Optimum

The Miocene Climatic Optimum (MCO) is an intriguing period of global climate history. Spanning from approximately 17 to 14 Ma, the MCO saw increased concentrations of greenhouse gasses and a rise in global temperature of 6 to 7 degrees Celsius. The MCO disrupted the long-term cooling trend of the Cenozoic and is often invoked as a potential analogue for understanding contemporary global climate change. It is not well understood, however, if and how the dynamics that drove the MCO (e.g., orbital pacing) may have conditioned regional-scale climate phenomena, particularly those associated with the interior of continents. Here we establish detailed, orbital-scale, terrestrial environmental responses to the MCO using magneto-cyclostratigraphic chronology. We identify six drought events in the Asian interior that are associated with prominent δ¹³C positive excursions, δ¹⁸O cooling Mi-events, global SST and sea-level fluctuations, as well as with the 405-kyr eccentricity band. We also document antiphase variability of precipitation across the monsoon-westerly influenced boundary. We contend that a predominant long eccentricity signal was of overriding significance as an orbital factor in regulating the rhythm of climatic change during the MCO.