The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, m...The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400 m-thick lacustrine section in Wenshan （Yunnan）, previously thought to be Late Mio- cene. These new data suggest an older age, ca. 15.2-16.5 Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter （3 Corg）, total organic carbon （TOC）, total nitrogen （TN） and C/N ratios at a high sample resolution to： （1） reconstruct the palaeoenvironmental changes in the lake catchment area, and （2） infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97 Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.展开更多
基金The authors are grateful to two anonymous reviewers for their constructive comments, which significantly improved the manuscript. The authors thank fellow members of staff of the Palaeoecology group in Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during sample collection and productive critical discussions Professor Yun Fu from the Central Laboratory of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during the TN mea- surements+1 种基金 Dr. Olesya V. Bondarenko, from the Russian Academy of Sciences, Vladivostok, for her help and support during sample preparation Yi-Min Tian from the Faculty of Land Resource Engi- neering, Kunming University of Science and Technology, for her assistance when preparing and observing thin sections. The authors are grateful to Dr. Andrea Kern from the USGS and Dr. Dayou Zhai from Yunnan University for fruitful discussions and suggestions to improve the manuscript. This study was supported by National Nat- ural Science Foundation of China （U1502231）, the CAS 135 Program （XTBG-F01）, and a grant from the China Scholarship Council to J. Lebreton Anberr6e （2013GCX606）. Shihu Li and Chenglong Deng acknowledge support from the National Natural Science Foundation of China （41404056）, and the State Key Laboratory of Lithospheric Evolution （11431780）. Shu-Feng Li was supported by the Foundation of the State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, CAS （15310）. This work is part of the NECLIME （Neogene Climate of Eurasia） network.
文摘The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400 m-thick lacustrine section in Wenshan （Yunnan）, previously thought to be Late Mio- cene. These new data suggest an older age, ca. 15.2-16.5 Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter （3 Corg）, total organic carbon （TOC）, total nitrogen （TN） and C/N ratios at a high sample resolution to： （1） reconstruct the palaeoenvironmental changes in the lake catchment area, and （2） infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97 Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.
