The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorpholog...The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.展开更多
Short cores of about 80-cm retrieved from three main basins of the deepwater areas in Qinghai Lake, the largest inland enclosed lake in China, were studied. Stable isotopes of authigenic carbonates, grain-size, carbon...Short cores of about 80-cm retrieved from three main basins of the deepwater areas in Qinghai Lake, the largest inland enclosed lake in China, were studied. Stable isotopes of authigenic carbonates, grain-size, carbonate and organic matter content at 5-year resolution are used to reconstruct the climatic history over the last 800 years in the Northeastern Tibetan Plateau. Chronology was established according to 210Pb dating and 137Cs methods and the core correlation. It is found that cores from different deep basins of the lake can be well correlated. The sedimentary rate is highest in the western basin of the lake and lowest in the east. In the southern basin of the lake where the short core Qing-6 is located, the recent average sedimentation rate is 0.1004 cm/yr. Variations in effective precipitation recorded by the oxygen isotopes and grain size data during the last 800 years are consistent with the glacial accumulation record form the Dunde and Guliya ice cores. A dry climate lasted for 300 years from 1200 AD to 1500 AD, followed by a wet period from 1500 to 1560 AD. The two dry periods, 1560 to 1650 AD and 1780 to 1850 AD, were the results of southwest monsoon weakening. The effective precipitation generally increased since 1650 AD due to the strengthening of the Asian Southwest Monsoon, resulting in a wet period until the 1950s. Except the early stage, the Little Ice Age on the Plateau is characterized by increased effective moisture. Organic mat- ter content, with nearly 200-year cycles, shows similar trend with the atmospheric delta carbon-14 before the 1850s, indicating that the bioproductivity responds to solar activity.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40125001)the Hundred Talent Project of CAS and the International Collaboration Project(Grant No.2002CB714004).
文摘The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.
基金supported by the Outstanding Young Scholar Project of the National Natural Science Foundation of China(NSFC)(Grant No.40125001)the NSFC international corporation supporting project(Grant No.49950131678)the British Counci1(Grant No.PEK/0992/306).
文摘Short cores of about 80-cm retrieved from three main basins of the deepwater areas in Qinghai Lake, the largest inland enclosed lake in China, were studied. Stable isotopes of authigenic carbonates, grain-size, carbonate and organic matter content at 5-year resolution are used to reconstruct the climatic history over the last 800 years in the Northeastern Tibetan Plateau. Chronology was established according to 210Pb dating and 137Cs methods and the core correlation. It is found that cores from different deep basins of the lake can be well correlated. The sedimentary rate is highest in the western basin of the lake and lowest in the east. In the southern basin of the lake where the short core Qing-6 is located, the recent average sedimentation rate is 0.1004 cm/yr. Variations in effective precipitation recorded by the oxygen isotopes and grain size data during the last 800 years are consistent with the glacial accumulation record form the Dunde and Guliya ice cores. A dry climate lasted for 300 years from 1200 AD to 1500 AD, followed by a wet period from 1500 to 1560 AD. The two dry periods, 1560 to 1650 AD and 1780 to 1850 AD, were the results of southwest monsoon weakening. The effective precipitation generally increased since 1650 AD due to the strengthening of the Asian Southwest Monsoon, resulting in a wet period until the 1950s. Except the early stage, the Little Ice Age on the Plateau is characterized by increased effective moisture. Organic mat- ter content, with nearly 200-year cycles, shows similar trend with the atmospheric delta carbon-14 before the 1850s, indicating that the bioproductivity responds to solar activity.
