The middle Miocene was a key period in Earth’s history as climate changed from one of the warmest phases of the Cenozoic Era, the Miocene Climatic Optimum (MCO), to colder conditions with the establishment of permanent ice sheets on Antarctica. This climate change had a profound impact on terrestrial ecosystems affecting vegetation worldwide. However, the scarceness of detailed pollen data at short-scale resolution for this time period precludes us from a deep understanding of environmental and vegetation changes at millennial-scales. Here, we present palynological data from a new sedimentary sequence from the Gračanica open cast mine (Bugojno Basin, Bosnia and Herzegovina), which shows significant changes in the environment and lake sedimentation, probably related with orbital-scale climate dynamics during the middle Miocene. This study also shows that high-amplitude climate variations characterised the middle Miocene climatic optimum (MCO; ~ 16.8–14.7 Ma). Statistical analysis and sedimentary rates suggest that eccentricity- and precession-dominated orbital-scale variability is recorded in the studied core. Warmest conditions are registered at the base of the studied section that could be correlated with an eccentricity maximum at the end of the MCO. A cooling trend is recorded since then and until the top of the sedimentary sequence, with coldest maxima, tentatively correlated with a minimum in eccentricity and insolation. Smaller-scale cyclical climatic events (i.e. warm-dry vs. cold-humid) observed in the vegetation and corresponding with lake-level variations are observed in this study that seems to be related with precession cyclicity. This study suggests that sedimentation in this lake basin lasted for about 200 kyr and was strongly conditioned by climate at the beginning of the middle Miocene climate transition.

中文翻译：

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受轨道尺度变化控制的中新世中期气候振荡触发了Dinarides湖系统（波斯尼亚和黑塞哥维那的布戈尼诺盆地）的环境和植被变异性

中新世中期是地球历史上的关键时期，因为气候从新生代最温暖的时期之一-中新世最佳气候（MCO）到南极洲永久性冰盖的变冷而变冷。这种气候变化对影响全球植被的陆地生态系统产生了深远影响。但是，由于这段时间缺乏以小规模分辨率获得的详细花粉数据，这使我们无法深入了解千禧年规模的环境和植被变化。在这里，我们展示了来自Gračanica露天矿（波斯尼亚和黑塞哥维那的布戈尼诺盆地）的一个新的沉积序列的孢粉数据，该数据显示了环境和湖泊沉积的重大变化，可能与中新世中期的轨道尺度气候动态有关。这项研究还表明，中新世中期气候最佳（MCO；〜16.8-14.7 Ma）是高幅度气候变化的特征。统计分析和沉积速率表明，在研究的岩心中记录了偏心率和旋进为主的轨道尺度变化。最热的条件记录在所研究部分的底部，这可能与MCO末端的最大离心率相关。此后一直记录着冷却趋势，直到沉积序列的顶部，最大的冷值暂时与最小的离心率和日照强度相关。在这项研究中观察到在植被中观测到的小规模周期性气候事件（即暖干与寒冷湿润），并与湖泊水位变化相对应，这似乎与进动的周期性有关。