Middle Miocene climate of southwestern Anatolia from multiple botanical proxies

Abstract

The middle Miocene climate transition (MMCT) was a phase of global cooling possibly linked to decreasing levels of atmospheric CO2. The MMCT coincided with the European Mammal Faunal Zone MN6. From this time, important biogeographic links between Anatolia and eastern Africa include the hominid Kenyapithecus. Vertebrate fossils suggested mixed open and forested landscapes under (sub) tropical seasonal climates for Anatolia. Here, we infer the palaeoclimate during the MMCT and the succeeding cooling phase for a middle Miocene (14.8-13.2 Ma) intra-montane basin in southwestern Anatolia using three palaeobotanical proxies: (i) Koppen signatures based on the nearest living-relative principle; (ii) leaf physiognomy analysed with the Climate Leaf Analysis Multivariate Program (CLAMP); (iii) genus-level biogeographic affinities of fossil flora with modern regions. The three proxies reject tropical and hot subtropical climates for the MMCT of southwestern Anatolia and instead infer mild warm temperate C climates. Koppen signatures reject summer-dry Cs climates but cannot discriminate between fully humid Cf and winter-dry Cw; CLAMP reconstructs Cf climate based on the low X3.wet/X3. dry ratio. Additionally, we assess whether the palaeobotanical record resolves transitions from the warm Miocene Climatic Optimum (MCO, 16.8-14.7Ma) to the MMCT (14.7-13.9 Ma), and a more pronounced cooling at 13.9-13.8 Ma, as reconstructed from benthic stable isotope data. For southwestern Anatolia, we find that arboreal taxa predominate in MCO flora (MN5), whereas in MMCT flora (MN6) abundances of arboreal and non-arboreal elements strongly fluctuate, indicating higher structural complexity of the vegetation. Our data show a distinct pollen zone between MN6 and MN7 + 8 dominated by herbaceous taxa. The boundary between MN6 and MN7 + 8, roughly corresponding to a first abrupt cooling at 13.9-13.8 Ma, might be associated with this herb-rich pollen zone.