Middle Miocene climate evolution in the Northern Mediterranean region (Digne-Valensole basin, SE France)

Abstract. During the Middle Miocene, the Earth shifted from a warm state, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder state associated with the formation of extensive and permanent ice sheets on Antarctica. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma) strongly affected the composition and structure of major biomes, ocean circulation, as well as precipitation patterns. Although Middle Miocene climate dynamics are well documented in marine records, our knowledge of terrestrial climate change is not well constrained. Here we present a long-term (23–13 Ma) stable (𝛿¹³C, 𝛿¹⁸O) and clumped (∆₄₇) isotope record of soil carbonates from a northern Mediterranean Alpine foreland basin (Digne-Valensole Basin, France). ∆₄₇-derived soil carbonate formation temperatures indicate a highly dynamic dry season temperature pattern that is consistent with multiple periods of reorganization of atmospheric circulation during the MCO. We propose that changes in atmospheric circulation patterns modified the seasonality of precipitation and, ultimately, the timing of pedogenic carbonate formation. Consequently, ∆₄₇ soil carbonate temperature data record the combined effects of long-term regional temperature and carbonate formation seasonality change. The data are consistent with the existence of a proto-Mediterranean climate already during certain MCO time intervals. Following the MMCT, the stable and clumped isotope record displays pronounced cooling after 13.8 Ma accompanied by a rather large (-5.0 %) decrease in soil water 𝛿¹⁸O values. Our northern Mediterranean foreland basin climate record shares strong similarities with time-equivalent records from the terrestrial European mid-latitudes and the global oceans and enhances our understanding of the circum-Alpine Middle Miocene terrestrial climate dynamics.