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Black Sea rivers capture significant change in catchment-wide mean annual temperature and soil pH during the Miocene-to-Pliocene transition

Vasiliev, Iuliana, Reichart, Gert-Jan, Krijgsman, Wout, Mulch, Andreas
Global and planetary change 2019 v.172 pp. 428-439
Miocene epoch, Pliocene epoch, air temperature, alkaline soils, basins, biomarkers, climatic factors, cold, cooling, hinterland, hydrogen, rivers, sea level, soil pH, Black Sea
The Neogene sedimentary successions of the Black Sea basin are ideal to study ancient paleoclimatic and hydrological changes in the Eurasian continental interior. Previous investigations revealed several phases of strongly enhanced evaporitic and dry conditions in the late Miocene. Here, we present the first reconstructed mean annual air temperature (MAAT) and soil pH data, combined with compound specific hydrogen isotopic (δD) records for the late Miocene to early Pliocene Black Sea basin, based on the analyses of biomarkers. Our MAAT, pH and δD data indicate that in the latest Tortonian (~8–7 Ma) mean annual air temperatures were approximately 5° higher than today, and that dry and warm climatic conditions prevailed. The early Messinian (7–6 Ma) is marked by a gradual change towards more humid, but still warm, conditions. The MAAT record shows a sharp decrease from 16 to 8 °C during the late Messinian (6.2–5.8 Ma) coinciding with a change towards extremely dry conditions. This cold and dry interval correlates to the time span marked by the late Miocene cooling of the northern hemisphere, and may also reflect a sea level change, restricting the Azov/Taman basin from the Black Sea. The calculated soil pH values in the range 7.1 to 7.7 are indicative for alkaline soils, such of those in the northern Eurasian hinterland, indicating a dominant northern Black Sea riverine source for the soil biomarkers. Finally, the Pliocene is marked by warmer conditions and lower soil pH, indicating a revival of the climatic conditions that characterized the Black Sea area during the late Messinian.